spectroscopy ultraviolet-visible spectroscopy infrared spectroscopy nuclear magnetic resonance mass...

SPECTROSCOPY Ultraviolet-Visible Spectroscopy

Infrared Spectroscopy Nuclear Magnetic Resonance

Mass Spectrometry:

Tools for Structure Determination

Hadi PoerwonoFakultas Farmasi

Universitas Airlangga

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Determining the Structure of an Organic Compound

The analysis of the outcome of a reaction requires that we know the full structure of the products as well as the reactants

In the 19th and early 20th centuries, structures were determined by synthesis and chemical degradation that related compounds to each other

Physical methods now permit structures to be determined directly. We will examine:• mass spectrometry (MS)• infrared (IR) spectroscopy• nuclear magnetic resonance spectroscopy (NMR)• ultraviolet-visible spectroscopy (UV-Vis)

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Introduction Spectroscopy: the study of the interaction of energy

with matter Energy applied to matter can be absorbed, emitted, cause a

chemical change, or be transmitted Spectroscopy can be used to elucidate the structure of a molecule

Examples of Spectroscopy Infrared (IR) Spectroscopy

Infrared energy causes bonds to stretch and bend IR is useful for identifying functional groups in a molecule

Nuclear Magnetic Resonance (NMR) Energy applied in the presence of a strong magnetic field causes absorption by

the nuclei of some elements (most importantly, hydrogen and carbon nuclei) NMR is used to identify connectivity of atoms in a molecule

Mass Spectrometry (MS) Molecules are converted to ions by one of several methods (including

bombardment by a beam of electrons) The ions formed may remain intact (as molecular ions, M+), or they may fragment The resulting mixture of ions is sorted by mass/charge (m/z) ratio, and detected Molecular weight and chemical formula may be derived from the M+ and M+1 ions Molecular structure may be deduced from the distribution of fragment ions

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The Electromagnetic Spectrum Electromagnetic radiation has the characteristics of both waves

and particles The wave nature of electromagnetic radiation is described by

wavelength or frequency The relationship between wavelength (or frequency) and energy

(E) is well defined

Wavelength and frequency are inversely proportional = c/ The higher the frequency, the greater the energy of the wave The shorter the wavelength, the greater the energy of the wave

E =hc

where c = velocity of light

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Wave Parameters

PeriodPeriod (p) (p) – – the time required for one cycle to pass a fixed point in space. the time required for one cycle to pass a fixed point in space.

Time or Distance-

+

Ele

ctri

c F

ield

0

Amplitude (A)

Wavelength ()

FrequencyFrequency ( ()) – – the number of cycles which pass a fixed point in space per the number of cycles which pass a fixed point in space per second. second.

= 1/p ( s= 1/p ( s-1-1 = Hz ) = Hz )

••depends on the source, but is independent of the depends on the source, but is independent of the propagating (transmitting) material.propagating (transmitting) material.AmplitudeAmplitude (A) (A) – – The maximum length of the electric vector in the wave The maximum length of the electric vector in the wave

(Maximum height of a wave). (Maximum height of a wave).

WavelengthWavelength ( ()) – – The distance between two identical adjacent points in a wave The distance between two identical adjacent points in a wave (usually maxima or minima). (usually maxima or minima).

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The Electromagnetic Spectrum The electromagnetic spectrum covers a wide range of wavelengths.

The divisions are based on the methods used to produce and observe the various types of radiation.

For example, the wavelength range for gamma rays and x-rays overlap. If the source is man-made, the radiation is usually considered x-rays. If the radiation is naturally occurring, the radiation is usually considered gamma rays.

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Types spectroscopic methods based on EM radiation.

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(UV-Vis) Infrared Spectroscopy

Nuclear Magnetic ResonanceMass Spectrometry:


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Internal Energy of Molecules

Etotal = Etrans+Eelec+Evib+Erot+Enucl

Eelec: electronic transitions (UV, X-ray)

Evib: vibrational transitions (Infrared)

Erot: rotational transitions (Microwave)

Enucl: nucleus spin (nuclear magnetic resonance) or (MRI: magnetic resonance imaging)

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Electronic Spectroscopy

Ultraviolet (UV) and visible (VIS) spectroscopy This is the earliest method of molecular spectroscopy. A phenomenon of interaction of molecules with ultraviolet

and visible lights. Absorption of photon results in electronic transition of a

molecule, and electrons are promoted from ground state to higher electronic states.

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Ultraviolet-Visible Spectroscopy Conjugated compounds absorb energy in the ultraviolet (UV) and

visible (Vis) regions on the electromagnetic spectrum The wavelength of radiation absorbed and the intensity of the absorption depend

on the structure of the molecule

UV-Vis Spectrophotometers A UV-Vis spectrum is typically measured from 200-800 nm,

spanning the near UV and visible regions

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Ultraviolet: 190~400nm Violet: 400 - 420 nm Indigo: 420 - 440 nm Blue: 440 - 490 nm Green: 490 - 570 nm Yellow: 570 - 585 nm Orange: 585 - 620 nm Red: 620 - 780 nm

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The wavelength of maximum absorption (max) is reported in units of nanometers (nm)

Molar absorptivity ( is also reported Is the intensity of the absorption A is the observed absorbance, C is the molar concentration of the sample and l is

length of the sample cell in centimeters

Example: UV absorption spectrum of 2,5-dimethyl-2,4-hexadiene in methanol at a concentration of 5.95 x 10-5 M in a 1.0 cm cell

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→

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UV and Visible Spectroscopy

In structure determination : UV-VIS spectroscopy is used to detect the presence of chromophores like dienes, aromatics, polyenes, and conjugated ketones, etc.

Absorbing species containing p, s, and n electrons

Absorption of ultraviolet and visible radiation in organic molecules is restricted to certain functional groups (chromophores) that contain valence electrons of low

excitation energy.

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Terms describing UV absorptions

1. Chromophores: functional groups that give electronic transitions.

2. Auxochromes: substituents with unshared pair e's like OH, NH, SH ..., when attached to chromophore they generally move the absorption max. to longer λ.

3. Bathochromic shift: shift to longer , also called red shift.

4. Hypsochromic shift: shift to shorter , also called blue shift.

5. Hyperchromism: increase in ε of a band.

6. Hypochromism: decrease in ε of a band.

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UV regions

The UV region is divided to two parts:

a. The near UV region: 190-400 nm.

b. The far or vacuum UV region: below 190 nm.

The far UV region has interference due to

absorption of oxygen, which must be removed or flushed with nitrogen in the spectrometer to obtain the spectra of sample.

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Absorbing Species Absorbing species containing Absorbing species containing , , , and , and nn electrons electrons

((organic compoundsorganic compounds).).

BondingBonding AntibondingAntibonding

FormaldehydeFormaldehyde

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Observed Electronic Transitions

•• ** and and n n ** are high energy, short wavelength transitions. are high energy, short wavelength transitions.

-- ** < 185 nm (Vacuum UV) < 185 nm (Vacuum UV)

-- n n ** = 150 – 250 nm (mainly = 150 – 250 nm (mainly vac. UV) vac. UV)

-- Very difficult to measure Very difficult to measure

•• n n ** and and ** 200 – 700 nm 200 – 700 nm

-- The most important and useful The most important and useful transitions in molecular UV transitions in molecular UV spectroscopy. spectroscopy.

-- Molar absorptivities (Molar absorptivities (): ):

n n ** 10 – 100 L cm 10 – 100 L cm-1-1 mol mol-1-1

** 1000 – 10,000 L cm 1000 – 10,000 L cm-1-1 mol mol-1-1

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Transitions

An electron in a bonding s orbital is excited to the corresponding antibonding orbital. The energy required is large. For example, methane (which has only C-H bonds, and can only undergo transitions) shows an absorbance maximum at 125 nm. Absorption maxima due to transitions are not seen in typical UV-VIS spectra (200 - 700 nm)

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n Transitions

Saturated compounds containing atoms with lone pairs (non-bonding electrons) are capable of n transitions. These transitions usually need less energy than transitions. They can be initiated by light whose wavelength is in the range 150 - 250 nm. The number of organic functional groups with n peaks in the UV region is small.

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n and Transitions

Most absorption spectroscopy of organic compounds is based on transitions of n or electrons to the excited state.

These transitions fall in an experimentally convenient region of the spectrum (200 - 700 nm). These transitions need an unsaturated group in the molecule to provide the electrons.

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UV/VIS

Vacuum UV or Far UV (λ<190 nm )

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Chromophores - Functional groups that absorb longer wavelength UV/Vis radiation. Molecules that contain unsaturated absorbing centers (double bonds).

•• Multiple chromophores have little effect on Multiple chromophores have little effect on maxmax but increase but increase . .

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Chromophore Excitation max, nm Solvent

C=C →* 171 hexane

C=On→*→*

290180

hexanehexane

N=On→*→*

275200

ethanolethanol

C-X X=Br, I

n→*n→*

205255

hexanehexane

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Auxochrome - Functional group that does not absorb UV radiation but shifts theax and increases when adjacent to a chromophore.

•• Usually have a pair of non-bonding electrons that interact with the Usually have a pair of non-bonding electrons that interact with the electrons of the chromophore. electrons of the chromophore.

•• Common auxochromes are hydroxides and amines. Common auxochromes are hydroxides and amines.

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Absorption Maxima for Nonconjugated and Conjugated Dienes In UV-Vis spectroscopy the electrons are excited from lower

energy levels to higher ones The electron is generally excited from the highest occupied molecular orbital

(HOMO) to the lowest unoccupied molecular orbital (LUMO) Alkenes and nonconjugated dienes have absorptions below 200 nm because the

energy difference between the HOMO and LUMO is large In conjugated dienes these energy levels are much closer together and the

wavelengths of absorption are longer than 200 nm

Ethene has max at 171 nm and 1,3-butadiene has max at 217 nm

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Conjugation•• Shifts Shifts maxmax to longer to longer and and is greater than expected due to the additive is greater than expected due to the additive

effect of conjugated double bonds. effect of conjugated double bonds.

•• Conjugation causes delocalization of Conjugation causes delocalization of electrons stabilizing electrons stabilizing **, , therefore shifting absorbance to longer wavelength (lower energy). therefore shifting absorbance to longer wavelength (lower energy).

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The longer the conjugated system, the smaller the energy difference between the HOMO and the LUMO

A smaller energy gap results in longer max in the ultraviolet -visible spectrum

-Carotene has 11 conjugated double bonds and an absorbance maximum at 497 nm which is in the blue-green region of the visible spectrum

-Carotene is perceived as red-orange, the complementary color of blue-green -Carotene is a precursor of vitamin A and a compound that imparts its orange

color to carrots

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The longer the conjugated system, the smaller the energy difference between the HOMO and the LUMO

A smaller energy gap results in longer max in the ultraviolet -visible spectrum

Lycopene also has 11 conjugated double bonds. It has an absorption maximum at 505 nm, and it absorbs there intensely

Approximately 0.02 g of lycopene can be isolated from 1 kg of fresh, ripe tomatoes Lycopene is a compound partly responsible for the red color of tomatoes

Carbonyl compounds also absorb light in the UV region An unshared (n) electron on oxygen is promoted to a * orbital

CH3

CH3

CH3 CH3

CH3 CH3 CH3

H3C

H3CCH3

Lycopene

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Aromatic Species•• Aromatic compound have three sets of bands arising from Aromatic compound have three sets of bands arising from **

transitions. transitions.

Benzene:Benzene:

184 nm (184 nm ( ~ 60,000) ~ 60,000)

EE22 band at 204 nm ( band at 204 nm ( = 7900) = 7900)

B band at 256 nm (B band at 256 nm ( = 200) = 200)

•• Each band has fine structure from Each band has fine structure from vibrational transitions that are reduced vibrational transitions that are reduced or disappear in polar solvents.or disappear in polar solvents.

Ultraviolet-Visible Spectra of Aromatic Compounds The conjugated electron of a benzene ring give characteristic

ultraviolet absorptions that indicate the presence of a benzene ring in an unknown compound

Benzene derivatives give an absorption band of moderate intensity near 205 nm and a less intense band at 250-275 nm

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Ultraviolet-Visible Spectra of Aldehydes and Ketones The carbonyl groups of saturated aldehydes and ketones give a

weak absorption band in the UV region between 270 and 300 nm. This band is shifted to longer wavelengths (300350 nm) when the

carbonyl group is conjugated with a double bond

Analytical Uses of UVVis Spectroscopy UVVis spectroscopy can be used in the structure elucidation of

organic molecules to indicate whether conjugation is present in a given sample

Although conjugation in a molecule may be indicated by data from IR, NMR, or mass spectrometry, UVVis analysis can provide corroborating information

A more widespread use of UVVis spectroscopy, however, has to do with determining the concentration of an unknown sample

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Solvent effects

Promotion of electron from G.S. to E.S. leads to more polar excited state that is more easily stabilized by polar solvent associations (H-bonds). In going from nonpolar to polar solvents the fine vibronic structure is smoothed into a broad band.

For * transition, the * state is more polar and stabilized more in polar solvent relative to nonpolar one, thus in going from nonpolar to polar solvent there is a red shift or bathochromic shift (increase in max, decrease in ΔE).

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Solvent effects For n * transition, the n state is much more

easily stabilized by polar solvent effects (H-bonds and association), so in going from nonpolar to polar solvent there is a blue shift or hypsochromic shift (decrease in max, increase in ΔE).

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heptanemethanol

Hypsochromic shiftO

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Solvent Effects

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Instrumentation

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Components of a SpectrophotometerLight Source

Deuterium Lamps － a truly continuous spectrum in the ultraviolet region is produced by electrical excitation of deuterium at low pressure. (160nm~375nm)

Tungsten Filament Lamps － the most common source of visible and near infrared radiation.

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Components of a Spectrophotometer

Monochromator

Used as a filter: the monochromator will select a narrow portion of the spectrum (the bandpass) of a given source

Used in analysis: the monochromator will sequentially select for the detector to record the different components (spectrum) of any source or sample emitting light.

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Single and Double Beam Spectrometer

Single-Beam: There is only one light beam or optical path from the source through to the detector.

Double-Beam: The light from the source, after passing through the monochromator, is split into two separate beams-one for the sample and the other for the reference.

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SPECTROSCOPY Ultraviolet-Visible Spectroscopy Infrared Spectroscopy (IR)

Nuclear Magnetic ResonanceMass Spectrometry:


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Absorption Spectra

Molecules - 3 types of Spectral Energyo Electronic Energy (UV/Vis)

• Absorption or emission in ultraviolet and visible region (27,000 cm-1 to 13,000 cm-1)

o Rotational Energy (microwave)• Absorption in far infrared region (400 cm-1

to 50 cm-1)o Vibrational Energy (infrared)

• Absorption in near, mid, and far infrared region (12,800 cm-1 to 50 cm-1)

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Theory of Infrared Absorption Spectroscopy

•• IR photons have low energy. The only transitions that have IR photons have low energy. The only transitions that have comparable energy differences are molecular vibrations and comparable energy differences are molecular vibrations and rotations.rotations.

Introduction

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Infrared (IR) SpectrumInfrared (IR) Spectrum

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FT-IR Energy Spectra

Infrared Regions Near IR region (12,800 cm-1 to 4001 cm-1) Mid IR region (4000 cm-1 to 400 cm-1) Far IR region (400 cm-1 to 50 cm-1)

Chemical Analysis Focus on Mid IR region (4000 cm-1 to 400 cm-1) Fingerprint region (1430 cm-1 to 830 cm-1) “Salt Form” region (3500 cm-1 to 2000 cm-1)

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Theory of Infrared Absorption Spectroscopy

•• In order for IR absorbance to occur two conditions must be met: In order for IR absorbance to occur two conditions must be met:

Introduction

1.1. There must be a change in the dipole moment of the molecule as There must be a change in the dipole moment of the molecule as a result of a molecular vibration (or rotation). The change (or a result of a molecular vibration (or rotation). The change (or oscillation) in the dipole moment allows interaction with the oscillation) in the dipole moment allows interaction with the alternating electrical component of the IR radiation. Symmetric alternating electrical component of the IR radiation. Symmetric molecules (or bonds) do not absorb IR radiation since there is no molecules (or bonds) do not absorb IR radiation since there is no dipole moment. dipole moment.

2.2. If the frequency of the radiation matches the natural frequency of If the frequency of the radiation matches the natural frequency of the vibration (or rotation), the IR photon is absorbed and the the vibration (or rotation), the IR photon is absorbed and the amplitude of the vibration increases.amplitude of the vibration increases.

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3.3. E = hE = h•• There are three types of molecular transitions that occur in IR There are three types of molecular transitions that occur in IR

a)a) Rotational transitionsRotational transitions

•• When an asymmetric molecule rotates about its center of mass, the When an asymmetric molecule rotates about its center of mass, the dipole moment seems to fluctuate.dipole moment seems to fluctuate.

•• E for these transitions correspond to E for these transitions correspond to < 100 cm< 100 cm-1 -1

•• Quite low energy, show up as sharp lines that subdivide vibrational Quite low energy, show up as sharp lines that subdivide vibrational peaks in gas phase spectra.peaks in gas phase spectra.

b)b) Vibrational-rotational transitionsVibrational-rotational transitions

•• complex transitions that arise from changes in the molecular dipole complex transitions that arise from changes in the molecular dipole moment due to the combination of a bond vibration and molecular moment due to the combination of a bond vibration and molecular rotation.rotation.

c)c) Vibrational transitionsVibrational transitions

•• The most important transitions observed in qualitative mid-IR The most important transitions observed in qualitative mid-IR spectroscopy. spectroscopy.

•• = 13,000 – 675 cm= 13,000 – 675 cm-1-1 (0.78 – 15 (0.78 – 15 M) M)

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Infrared Spectroscopy: An Instrumental Method for Detecting Functional Groups Electromagnetic radiation in the infrared (IR) frequency

range is absorbed by a molecule at certain characteristic frequencies Energy is absorbed by the bonds in the molecule and they vibrate

faster The bonds behave like tiny springs connecting the atoms

The bonds can absorb energy and vibrate faster only when the added energy is of a particular resonant frequency

The frequencies of absorption are very characteristic of the type of bonds contained in the sample molecule

The type of bonds present are directly related to the functional groups present

A plot of these absorbed frequencies is called an IR spectrum

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Infrared Spectrometer An infrared spectrometer detects the frequencies absorbed by the

sample molecule Light of all the various IR frequencies is transmitted to the

molecule and the frequencies absorbed are recorded The absorption frequencies are specified as wavenumbers in units

of reciprocal centimeters (cm-1) Alternatively the wavelength (l) in units of microns (mm) can be specified

The spectrum is a plot of frequency on the horizontal axis versus strength of absorption on the vertical axis

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There are different types of stretching and bending vibrations induced by the absorption of infrared energy

The actual relative frequency of vibration can be predicted Bonds with lighter atoms vibrate faster than those with heavier atoms

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Triple bonds (which are stiffer and stronger) vibrate at higher frequencies than double bonds

Double bonds in turn vibrate at higher frequencies than single bonds

The IR spectrum of a molecule usually contains many peaks These peaks are due to the various types of vibrations available to each of the

different bonds Additional peaks result from overtone (harmonic) peaks which are weaker and of

lower frequency The IR is a “fingerprint” of the molecule because of the unique and large number

of peaks seen for a particular molecule

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Interpreting IR Spectra Generally only certain peaks are interpreted in the IR

Those peaks that are large and above 1400 cm-1 are most valuable

Hydrocarbons The C-H stretching regions from 2800-3300 cm-1 is characteristic

of the type of carbon the hydrogen is attached to C-H bonds where the carbon has more s character are shorter,

stronger and stiffer and thus vibrate at higher frequency C-H bonds at sp centers appear at 3000-3100 cm-1 C-H bonds at sp2 centers appear at about 3080 cm-1 C-H bonds at sp3 centers appear at about 2800-3000 cm-1

C-C bond stretching frequencies are only useful for multiple bonds C-C double bonds give peaks at 1620-1680 cm-1 C-C triple bonds give peaks at 2100-2260 cm-1 These peaks are absent in symmetrical double and triple bonds

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Example: octane

Example: 1- hexyne

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Alkenes The C-H bending vibration peaks located at 600-1000 cm-1 can be

used to determine the substitution pattern of the double bond

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Example: 1-hexene

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Aromatic Compounds The C-C bond stretching gives a set of characteristic sharp peaks

between 1450-1600 cm -1 Example: Methyl benzene

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Infrared Spectra of Substituted Benzenes Benzene derivatives show several characteristic frequencies

C-H Stretching occurs near 3030 cm-1

Stretching motions of the ring give bands at 1450-1600 cm -1 and two bands near 1500 and 1600 cm-1

Monosubstituted benzenes show two strong absorptions at 690-710 cm-1 and 730-770 cm-1

Disubstituted benzenes show the following absorptions

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Other Functional Groups Carbonyl Functional Groups

Generally the carbonyl group gives a strong peak which occurs at 1630-1780 cm-1

The exact location depends on the actual functional group present

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Spectroscopic Properties of Aldehydes and Ketones IR Spectra of Aldehydes and Ketones

Aldehydes and ketones have strong carbonyl stretching frequencies in the 1665-1780 cm-1 region

Conjugation shifts the IR frequency about 40 cm-1 lower because the carbonyl has less double bond character

Single bonds stretch more easily than double bonds

Vibrations of the C-H bond in an aldehyde gives two weak but characteristic bands at 2700-2775 and 2820-2900 cm-1

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Carboxylic Acids The carbonyl peak at 1710-1780 cm-1 is very characteristic The presence of both carbonyl and O-H stretching peaks is a good

proof of the presence of a carboxylic acid

Example: propanoic acid

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Spectroscopic Properties of Acyl Compounds IR Spectra

The carbonyl stretching frequency varies according to the type of carboxylic acid derivative present

O-H stretching vibrations of the carboxylic acid give a broad band at 2500-3100 cm-1

N-H stretching vibrations of amides appear at 3140-3500 cm -1

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Example 1:Example 1: Calculate the force constant of the carbonyl bond in the Calculate the force constant of the carbonyl bond in the following spectrum.following spectrum.

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Alcohols and Phenols The O-H stretching absorption is very characteristic

In very dilute solutions, hydrogen bonding is absent and there is a very sharp peak at 3590-3650 cm-1

In more concentrated solutions, the hydroxyl groups hydrogen bond to each other and a very broad and large peak occurs at 3200-3550 cm -1

A phenol has a hydroxyl group directly bonded to an aromatic ring

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Spectroscopic Analysis of Phenols and Aryl Halides Infrared Spectra

Phenols show a characteristic absorption band (usually broad) arising from OH stretching in the 3400-3600 cm-1 region

Phenols and aryl halides also show the characteristic absorption that arise from their benzene rings

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Amines Very dilute solution of 1o and 2o amines give sharp peaks at 3300-

3500 cm-1 for the N-H stretching 1o amines give two peaks and 2o amines give one peak 3o have no N-H bonds and do not absorb in this region

More concentrated solutions of amines have broader peaks Amides have amine N-H stretching peaks and a carbonyl peak

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Spectroscopic Analysis of Amines Infrared Spectra

Primary and secondary amines are characterized by N-H stretching vibrations in the 3300-3555 cm -1 region

Primary amines give 2 absorptions (from symmetric and asymmetric stretching); secondary amines give one absorption

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How to approach the analysis of a spectrum

1. Is a carbonyl group present? The C=0 group gives rise to a strong absorption in the region 18201660 cm1. The peak is often the strongest in the spectrum and of medium width. You can’t miss it.

2. If the C=O is present, check the following types (if it is absent, go to 3).ACIDS Is OH also present?

Broad absorption near 34002400 cm1 (usually overlaps CH).AMIDES Is NH also present?

Medium absorption near 3400cm1; sometimes a double peak with equivalent halves.

ESTERS Is CO also present? Strong intensity absorption near 13001000 cm1 .

ANHYDRIDES Two C=O absorption near 1810 and 1760 cm1.ALDEHYDES Is aldehyde CH present?

Two weak absorption near 2850 and 2750cm1 on right side of the aliphatic CH absorption.

KETONES The preceding five choices have been eliminated.

3. If the C=O is absent:ALCOHOLS, PHENOLS Check for OH.

Broad absorption near 34003300 cm1. Confirm this by finding CO near 13001000 cm1.

AMINES Check for NH. Medium absorption(s) near 3400 cm1.

ETHERS Check for CO near 13001000 cm1 (and absence of OH near 3400 cm1).

1. Double bonds and/or aromatic rings C=C is a weak absorption near 1650 cm1. Medium to strong absorption in the region 16001450 cm1; this often imply an aromatic ring. Confirm the double bond or aromatic ring by consulting the CH region; aromatic and vinyl C–H occurs to the left of 3000 cm1 (aliphatic CH occurs to the right this value).

Triple bonds

C≡N is a medium, sharp absorption near 2250 cm1.

C≡C is a weak, sharp absorption near 2150 cm1.

Check also for acetylenic CH near 3300 cm1.

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How to approach the analysis of a spectrum

6. Nitro groups Two strong absorption at 16001530 cm1 and 13901300 cm1 .

7. Hydrocarbons

None of the preceding is found.

Major absorptions are in CH region near 3000 cm1.

Very simple spectrum; the only other absorptions appear near 1460 cm1 and 1375 cm1.

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Use of IR spectra

Identification of functional groups on a molecule – this is a very important tool in organic chemistry

Spectral matching can be done by computer software and library spectra

Since absorbance follows Beer’s Law, can do quantitative analysis

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Infrared (IR) SpectrometerInfrared (IR) Spectrometer

All modern instruments are All modern instruments are Fourier TransformFourier Transform instruments. instruments.

In all transmission experiments radiation from a In all transmission experiments radiation from a source is directed through the sample to a source is directed through the sample to a detector.detector.

To obtain an IR spectrum, the sample must be To obtain an IR spectrum, the sample must be placed in a “container” or cell that is transparent placed in a “container” or cell that is transparent in the IR region of the spectrum. in the IR region of the spectrum.

Sodium chloride or salt plates are a common Sodium chloride or salt plates are a common means of placing the sample in the light beam of means of placing the sample in the light beam of the instrument.the instrument.

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Michelson InterferometerMichelson Interferometer

Multiplexing (FT) SpectrometersMultiplexing (FT) Spectrometers

•• The source beam is split into two The source beam is split into two beams.beams.

•• One beam goes to a stationary One beam goes to a stationary mirror and the other goes to a mirror and the other goes to a moveable mirror.moveable mirror.

•• Movement of the mirror at a Movement of the mirror at a constant rate and recombination of constant rate and recombination of the two beams results in a signal the two beams results in a signal that is modulated by constructive that is modulated by constructive and destructive interference and destructive interference ((InterferogramInterferogram). ).

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•• The frequency of the The frequency of the radiation (radiation () is directly ) is directly related to the frequency related to the frequency of the interferogram (of the interferogram (ff). ).

c

f m2

= frequency of radiation= frequency of radiation

f f = frequency of inteferogram= frequency of inteferogram

mm = velocity of the mirror = velocity of the mirror

cc = speed of light (3.00 x 10 = speed of light (3.00 x 101010 cm/s) cm/s)

•• FT-IR spectrometers use a polychromatic source and collect the entire FT-IR spectrometers use a polychromatic source and collect the entire spectrum simultaneously and decode the spectrum by spectrum simultaneously and decode the spectrum by Fourier TransformFourier Transform. .

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FT-IR instrumentFT-IR instrument


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(NMR)Mass Spectrometry:


82

NMR involves absorption of energy in the radiofrequency range

83

Nuclear Magnetic Resonance (NMR) Spectroscopy The nuclei of protons (1H) and carbon-13 (13C), and certain other

elements and isotopes, behave as if they were tiny bar magnets When placed in a magnetic field and irradiated with radio frequency

energy, these nuclei absorb energy at frequencies based on their chemical environments

NMR spectrometers are used to measure these absorptions

Continuous-Wave (CW) NMR Spectrometers The oldest type of NMR spectrometer The magnetic field is varied as the electromagnetic radiation is kept

at a constant frequency Different nuclei absorb the electromagnetic energy based on their

chemical environment and produce peaks in different regions of the spectrum

84

Fourier Transform (FT) NMR Spectrometers The sample is placed in a constant (and usually very strong)

magnetic field The sample is irradiated with a short pulse of radio frequency

energy that excites nuclei in different environments all at once The resulting signal contains information about all of the absorbing

nuclei at once This signal is converted to a spectrum by a Fourier transformation FT NMR allows signal-averaging, which leads to enhancement of

real spectral signals versus noise The strong, superconducting magnets used in FTNMR

spectrometers lead to greater sensitivity and much higher resolution than continuous wave instruments

85

The NMR Spectrometer

86

NMR Signals

The number of signals shows how many different kinds of protons are present.

The location of the signals shows how shielded or deshielded the proton is.

The intensity of the signal shows the number of protons of that type.

Signal splitting shows the number of protons on adjacent atoms.

87

Chemical Shift: Peak Position in an NMR Spectrum Nuclei in different chemical environments in a molecule will

absorb at slightly different frequencies The position of the signals in the spectrum is called the “chemical

shift” There are two reasons for differences in the magnetic environment

for a proton The magnetic field generated by electrons circulating around the nucleus giving

the signal Local magnetic fields generated by electrons elsewhere in the molecule

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Example: 1,4-dimethylbenzene

The spectrum is measured on a delta () scale in units of parts per million (ppm) Lower frequency is to the left in the spectrum; these absorptions are said to be

downfield Higher frequency is to the right in the spectrum: these absorptions are said to be

upfield The small signal at 0 corresponds to an internal standard called

tetramethylsilane (TMS) used to calibrate the chemical shift scale The number of signals in the spectrum corresponds to the number of unique sets

of protons 1,4-dimethylbenzene has protons in two unique environments and so shows two

signals

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Integration of Peak Areas. The Integral Curve The area under each signal corresponds to the relative number of

hydrogen atoms in each unique environment within a molecule The height of each step in the integral curve is proportional to the area of the

signal underneath the step

Signal Splitting The signal from a given proton will be split by the effect of

magnetic fields associated with protons on adjacent carbons Characteristic peak patterns result from signal splitting that are

related to the number of protons on adjacent carbons Example: 1,1,2-trichloroethane

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Nuclear Spin: The Origin of the Signal The nuclei of certain elements and isotopes have spin states that

are quantized 1H has a spin quantum number I = 1/2 and has allowed spin states

of +1/2 or -1/2 Other nuclei with I = 1/2 are 13C, 19F and 31P and these also respond

to an external magnetic field Nuclei with I = 0 do not have spin (12C and 16O) and do not respond

to an external magnetic field The nuclei of NMR-active nuclei behave like tiny bar magnets In the absence of an external magnetic field these bar magnets are

randomly orientated In an external magnetic field they orient either with ( spin state)

or against ( spin state) the magnetic field

91

Nuclei aligned with the magnetic field are lower in energy than those aligned against the field

The nuclei aligned with the magnetic field can be flipped to align against it if the right amount of energy is added (E)

The amount of energy required depends on the strength of the external magnetic field

The stronger the external magnetic field, the higher the radio frequency energy required to flip the nuclear spin

At (a) there is no external magnetic field and therefore no energy difference between the two states

At (b) the external magnetic field is 1.41 Tesla and energy corresponding to a frequency of about 60MHz is needed to flip between the spin states

At (c) the external magnetic field is 7.04 Tesla energy corresponding to a frequency of about 300MHz is needed to flip between the spin states

92

Shielding and Deshielding of Protons Protons in an external magnetic field absorb at different

frequencies depending on the electron density around that proton High electron density around a nucleus shields the nucleus from

the external magnetic field Shielding causes absorption of energy at higher frequencies (more energy is

required for this nucleus to flip between spin states) - the signals are upfield in the NMR spectrum

Lower electron density around a nucleus deshields the nucleus from the external magnetic field

Deshielding causes absorption of energy at lower frequencies (less energy is required for this nucleus to flip between spin states) - the signals are downfield in the NMR spectrum

93

Electronegative atoms draw electron density away from nearby protons and therefore deshield them

Circulation of electrons leads to a local induced magnetic field The induced field can reinforce or diminish the external field sensed by a proton

(depending on the location of the proton), causing deshielding or shielding, respectively

Alkene and aromatic ring hydrogens are deshielded by the circulation of electrons.

A terminal alkyne hydrogen is shielded by the circulation of electrons.

94

Chemical Shift Chemical shifts are measured in relation to the internal reference

tetramethylsilane (TMS) The protons of TMS are highly shielded because of the strong electron donating

capability of silicon The signal for TMS is well away from most other proton absorptions

The scale for chemical shifts is independent of the magnetic field strength of the instrument (whereas the absolute frequency depends on field strength)

Thus, the chemical shift in units for protons on benzene is the same whether a 60 MHz or 300 MHz instrument is used

96

Chemical Shift Equivalent and Nonequivalent Protons

To predict the number of signals to expect in an NMR spectrum it is necessary to determine how many sets of protons are in unique environments

Chemically equivalent protons are in the same environment and will produce only one signal

Homotopic Hydrogens Hydrogens are chemically equivalent or homotopic if replacing

each one in turn by the same group would lead to an identical compound

97

Enantiotopic and Diastereotopic Hydrogen Atoms If replacement of each of two hydrogens by some group leads to

enantiomers, those hydrogens are enantiotopic In the absence of a chiral influence, enantiotopic hydrogens have the same

chemical shift and appear in the same signal

If replacement of each of two hydrogens by some group leads to diastereomers, the hydrogens are diastereotopic

Diastereotopic hydrogens have different chemical shifts and will give different signals

98

Signal Splitting: Spin-Spin Coupling The signal from a given proton will be split by the effect of

magnetic fields associated with protons on adjacent carbons Characteristic peak patterns result from signal splitting that are

related to the number of protons on adjacent carbons The effect of signal splitting is greatest between atoms separated by 3 or fewer

bonds

Signal splitting is not observed between homotopic or enantiotopic protons

Signal splitting occurs only when two sets of protons have different chemical shifts (i.e., are not chemical shift equivalent)

99

The magnetic field sensed by a proton (Ha) being observed is affected by the magnetic moment of an adjacent proton (Hb)

A proton (Hb) can be aligned with the magnetic field or against the magnetic field, resulting in two energy states for Hb

The observed proton (Ha) senses the two different magnetic moments of Hb as a slight change in the magnetic field; one magnetic moment reinforces the external field and one substracts from it

The signal for Ha is split into a doublet with a 1:1 ratio of peak areas

The magnitude of the splitting is called the coupling constant Jab and is measured in Hertz (Hz)

100

When two adjacent protons Hb are coupled to Ha, there are four possible combinations of the magnetic moments for the two Hbs

Two of these combinations involve pairings of magnetic moments that cancel each other, causing no net displacement of signal

One combination of magnetic moments reinforces and another subtracts from the applied magnetic field

Ha is split into a triplet having a 1:2:1 ratio of signal areas

101

When three adjacent protons are coupled to Ha, there are 10 possible combinations of the magnetic moments for the Hbs

Four unique orientations exist and so Ha is split into a quartet with intensities 1:4:4:1

102

The general rule for splitting is that if there are n equivalent protons on adjacent atoms, these will split a signal into n + 1 peaks

Coupled peaks have the same coupling constants J Comparison of coupling constants can help with the analysis of complex spectra

Several factors complicate analysis of NMR spectra Peaks may overlap Spin-spin coupling can be long-range (i.e., more than 3 bonds)

Splitting patterns in aromatic groups can be confusing A monosubstituted aromatic ring can appear as an apparent singlet or a complex

pattern of peaks

103

Much more complex splitting can occur when two sets of adjacent protons split a particular set of protons

In the system below, Hb is split by two different sets of hydrogens : Ha and Hc

Theortically Hb could be split into a triplet of quartets (12 peaks) but this complexity is rarely seen

The spectrum of 1-nitropropane shows splitting of Hb into only 6 peaks

105

Proton NMR Spectra and Rate Processes An NMR spectrometer is like a camera with a slow shutter speed The NMR spectrometer will observe rapid processes as if they

were a blur, i.e., only an average of the changes will be seen When a 1H NMR spectrum of very pure ethanol is taken, the

hydroxyl proton is split into a triplet by the two adjacent hydrogens

When an 1H NMR of regular ethanol is taken the hydroxyl proton is a singlet

Impure ethanol contains acid and base impurities which catalyze the exchange of hydroxyl protons

This rapid exchange is so fast that coupling to the adjacent CH2 is not observed

This process is called spin decoupling

106

Spin decoupling is typical in the 1H NMR spectra of alcohols, amines and carboxylic acids

The proton attached to the oxygen or nitrogen normally appears as a singlet because of rapid exchange processes

107

Carbon-13 NMR Spectroscopy 13C accounts for only 1.1% of naturally occurring carbon

12C has no magnetic spin and produces no NMR signal

One Peak for Each Unique Carbon Atom Since the 13C isotope of carbon is present in only 1.1% natural

abundance, there is only a 1 in 10,000 chance that two 13C atoms will occur next to each other in a molecule

The low probability of adjacent 13C atoms leads to no detectable carbon-carbon splitting

1H and 13C do split each other, but this splitting is usually eliminated by adjusting the NMR spectrophotometer accordingly

The process of removing the coupling of 1H to an attached carbon is called broadband (BB) proton decoupling

Most 13C NMR, therefore, consist of a single peak for each unique carbon

108

13C Chemical Shifts Just as in 1H NMR spectroscopy, chemical shifts in 13C NMR

depend on the electron density around the carbon nucleus Decreased electron density causes the signal to move downfield (desheilding) Increased electron density causes the signal to move upfield (sheilding)

Because of the wide range of chemical shifts, it is rare to have two 13C peaks coincidentally overlap

A group of 3 peaks at 77 comes from the common NMR solvent deuteriochloroform and can be ignored

109

Off-Resonance Decoupled Spectra Broad-band decoupling removes all information about the number

of hydrogens attached to each carbon Off-resonance decoupling removes some of the coupling of

carbons to hydrogens so that the coupled peaks will not overlap Use of off-resonance decoupled spectra has been replaced by use

of DEPT 13C NMR

DEPT 13C NMR DEPT (distortionless enhanced polarization transfer) spectra are

created by mathematically combining several individual spectra taken under special conditions

The final DEPT spectra explicitly show C, CH, CH2 , and CH3 carbons

To simplify the presentation of DEPT data, the broadband decoupled spectrum is annotated with the results of the DEPT experiments using the labels C, CH, CH2 and CH3 above the appropriate peaks

110

Example: 1-chloro-2-propanol (a) The broadband decoupled spectrum and (b) a set of DEPT

spectra showing the separate CH, CH2, and CH3 signals

111

Spectroscopy of Aromatic Compounds 1H NMR Spectra

Protons of benzene derivatives are highly deshielded and appear in the region 6.0 to 9.5

A ring current is induced in the benzene ring that reinforces the applied magnetic field in the region of the protons in benzene

In large annulenes protons pointing into the ring are highly sheilded

13C NMR Spectra Aromatic carbons generally appear in the 100-170 region

DEPT spectra will show these carbons to have one or no protons attached

112

Example : the spectrum of 4-N,N-diethylaminobenzaldehyde The assignment of carbons (d) and (c) is possible because carbons (d) should

have higher electron density than carbons (c), based on resonance structures

113

Given a molecular formula or mass spectrometric data,13C NMR can be used to recognize compounds with high symmetry

The spectrum below corresponds to the last isomer which can have only two peaks

114

Spectroscopic Analysis of Phenols and Aryl Halides 1H NMR

The position of the hydroxyl proton of phenols depends on concentration

In phenol itself the O-H proton is at 2.55 for pure phenol and at 5.63 for a 1% solution

Phenol protons disappear from the spectrum when D2O is added

The aromatic protons of phenols and aryl halides occur in the 7-9 region

13C NMR The carbon atoms of phenols and aryl halides appear in the region

135-170

115

NMR Spectra of Aldehydes and Ketones 13C NMR Spectra

Aldehyde and ketone carbonyl carbons give characteristic signals at 180-220

1H NMR Spectra Aldehyde protons give sharp signals at 9-12 The aldehyde proton often shows coupling to the protons on the -carbon Protons on the carbon generally appear at 2.0-2.3

116

1H NMR Spectra The hydrogens of carboxylic acids and their derivatives appear at 2.0-2.5 The carboxyl group proton appears downfield at 10-12

13C NMR Spectra The carbonyl carbon signal for carboxylic acids and their derivatives appears at

160 to 180

117

Spectroscopic Analysis of Amines 1H NMR

Primary and secondary amines have broad, uncoupled N-H peaks at 0.5-5 N-H protons will exchange with D2O and disappear from the 1H spectrum

Protons on carbons adjacent to the nitrogen appear at 2.2-2.9

118

13C NMR Spectra Carbons bonded to nitrogen exhibit 13C signals not as far downfield (20-70) as

carbons bonded to oxygen (40-80) due to the lesser electronegativity of nitrogen as compared to oxygen

The deshielding effect of the nitrogen atom decreases with distance

119



Mass Spectrometry (MS):Tools for Structure Determination

120

Mass Spectroscopy

Analogy of smashing a vase with a hammer, and determining what the vase looked like by putting the pieces back together

Difficulty is that all bonds can potentially break, but not all bonds break equally

.

.

ABCABC+

AB+ C+

A+ BC+

121

Important Mass Spectroscopy Terms

Molecular ion- peak where molecule is not broken, just lost an e– (ABC+ in this figure)

Fragment ions- all other ions Base peak- most abundant peak in spectrum (a fragment ion)

.

.

ABCABC+

AB+ C+

A+ BC+

122

Introduction to Mass Spectrometry (MS) A mass spectrometer produces a spectrum of masses based on

the structure of a molecule. A mass spectrum is a plot of the distribution of ion masses

corresponding to the formula weight of a molecule and/or fragments derived from it

The x-axis of a mass spectrum represents the masses of ions produced

The y-axis represents the relative abundance of each ion produced The pattern of ions obtained and their abundance is characteristic

of the structure of a particular molecule

123

The Mass SpectrometerOne common type is the Electron Impact Mass

Spectrometer (EI MS) Ionization (the formation of ions)

A molecule is bombarded with a beam of high energy electrons An electron may be dislodged from the molecule by the impact,

leaving a positively charged ion with an unpaired electron (a radical cation)

This initial ion is called the molecular ion (M+.) because it has the same molecular weight as the analyte

Fragmentation Excess vibrational energy is imparted to the molecular ion by

collision with the electron beam - this causes fragmentation The fragmentation pattern is highly characteristic of the structure of the molecule

124

Ion Sorting The fragments are sorted according to their mass to charge ratio,

(m/z) Most of the fragments detected have charge +1; the net effect is

sorting of the ions by mass (m/z, where z = +1) The charged molecular ion (M+) and fragments pass through an

analyzer that sorts the ions according to m/z One method of sorting involves directing the ions through a curved tube that

passes through a magnetic field; as the magnetic field is varied, ions of different m/z values successfully traverse the tube and reach the detector

After ion sorting the results are plotted as a spectrum with m/z on the horizontal axis and relative abundance of each ion on the vertical axis

125

The Mass Spectrum Data from a mass spectrometer can be represented as a graph or

table The most abundant (intense) peak in the spectrum is called the

base peak and is assigned a normalized intensity of 100% The masses are based on rounding of atom masses to the nearest

whole number (in low resolution mass spectroscopy) The data and fragmentation patterns for ammonia are as follows

The base peak for ammonia is the molecular ion, but this is often not the case

126

The small peak at m/z 18 comes from the small amount of 15N1H3 because of the small natural abundance of 15N compared to 14N

This peak is called an M+1 peak

127

Determination of Molecular Formulas and Molecular Weights The Molecular Ion and Isotopic Peaks

The presence of heavier isotopes one or two mass units above the common isotope yields small peaks at M+.+1 and M+.+2

The intensity of the M+.+1 and M+.+2 peaks relative to the M peak can be used to confirm a molecular formula

Example: In the spectrum of methane one expects an M+.+1 peak of 1.17% based on a 1.11% natural abundance of 13C and a 0.016% natural abundance of 2H

128

We use the following guides to determine the molecular formula.

1. Is M+. odd or even? According to the nitrogen rule, if it is even, then the compound must contain an even number of nitrogen atoms (zero is an even number).

For our unknown, M+. is even. The compound must have an even number of nitrogen atoms.

2. The relative abundance of the M+. + 1 peak indicates the number of carbon atoms. Number of C atoms = relative abundance of (M+. + 1) / 1.1

For our unknown, number of C atoms = 4.5 / 1.1 = 4.(This formula works because 13C is the most important contributor to the M+. + 1 peak and the approximate natural abundance of 13C is 1.1%).

3. The relative abundance of the M+. + 2 peak indicates the presence (or absence) of S, (4.4%); Cl (33%); or Br (98%).

For our unknown, M+. + 2 = 0.2%; thus we can assume that S, Cl, and Br are absent.

4. The molecular formula can now be established by determining the number of hydrogen atoms and adding the appropriate number of oxygen atoms, if necessary. For our unknown, the M+. peak at m/z 72 gives us the molecular weight. It also tells us (since it is even) that nitrogen is absent because C4N2 has a molecular weight (76) greater than that of our compound.

For a molecule composed of C and H only:H = 72 – (4 x 12) = 24, but C4H24 is impossible.

For a molecule composed of C, H and one O:H = 72 – (4 x 12) – 16 = 8 and thus our unknown has the molecular formula

C4H8O.

129

m/z

Intensity

(as percent of base peak) m/z

Intensity

(as percent of M+.)

27 59.0 72 M+. 100.0

28 15.0 73 M+. + 1 4.5

29 54.0 74 M+. + 2 0.3

39 23.0 Recalculated to base on M+.

41 60.0

42 12.0

43 79.0

44 100.0 (base)

72 73.0 M+.

73 3.3

74 0.2

Mass spectrum of an unknown compound

130

High-Resolution Mass Spectrometry Low-resolution mass spectrometers measure m/z values to the

nearest whole number High-resolution mass spectrometers measure m/z values to three

or four decimal places The high accuracy of the molecular weight calculation allows

accurate determination of the molecular formula of a fragment Example

One can accurately pick the molecular formula of a fragment with a nominal molecular weight of 32 using high-resolution MS

131

The exact mass of certain nuclides is shown below

132

Fragmentation In EI mass spectrometry the molecular ion is highly energetic and

can break apart (fragment) Fragmentation pathways are predictable and can be used to

determine the structure of a molecule The processes that cause fragmentation are unimolecular The relative ion abundance is extremely important in predicting

structures of fragments

Fragmentation by Cleavage at a Single Bond Cleavage of a radical cation occurs to give a radical and a cation

but only the cation is observable by MS In general the fragmentation proceeds to give mainly the most

stable carbocation In the spectrum of propane the peak at 29 is the base peak (most abundant) 100%

and the peak at 15 is 5.6%

133

Fragmentation Equations The M+. Ion is formed by loss of one of its most loosely held

electrons If nonbonding electron pairs or pi electrons are present, an electron from one of

these locations is usually lost by electron impact to form M+.

Loosely held nonbonding electrons on nitrogen and oxygen, and electrons in double bonds are common locations for an electron to be lost (i.e., where the remaining unshared electron in M+. resides)

In molecules with only C-C and C-H bonds, the location of the lone electron cannot be predicted and the formula is written to reflect this using brackets

134

Example: The spectrum of hexane

135

Example: spectrum of neopentane Fragmentation of neopentane shows the propensity of cleavage to occur at a

branch point leading to a relatively stable carbocation The formation of the 3o carbocation is so favored that almost no molecular ion is

detected

136

Carbocations stabilized by resonance are also formed preferentially

Alkenes fragment to give resonance-stabilized allylic carbocations

Carbon-carbon bonds next to an atom with an unshared electron pair break readily to yield a resonance stabilized carbocation

Z=N, O, or S R may be H

137

Carbon-carbon bonds next to carbonyl groups fragment readily to yield resonance stabilized acylium ions

138

Alkyl substituted benzenes often lose a hydrogen or alkyl group to yield the relatively stable tropylium ion

Other substituted benzenes usually lose their substitutents to yield a phenyl cation

139

Fragmentation by Cleavage of 2 Bonds The products are a new radical cation and a neutral molecule Alcohols usually show an M+.-18 peak from loss of water

Cycloalkenes can undergo a retro-Diels Alder reaction (section 13.11) to yield an alkadienyl radical cation

140

Carbonyl compounds can undergo a McLafferty Rearrangement Y may be R, H, OH, OR etc.

141

Mass Spectra of Aromatic Compounds The major ion in the mass spectrum of alkyl benzenes is m/z 91,

which corresponds to a benzyl cation (C6H5CH2+), which rearranges

to a tropylium ion (C7H7+)

Another common ion is the phenyl cation (C6H5+)

Mass Spectra of Amines The molecular ion in the mass spectrum of an amine has an odd

number mass (unless there is an even number of nitrogen atom in the molecule).

The peak for the molecular ion is usually strong for aromatic and cyclic aliphatic amines but weak for acyclic aliphatic amines.

Cleavage between the and carbons of aliphatic amines is a common mode of fragmentation.

142

Molekul dengan lebih dari satu atom yang memiliki isotop

Daerah ion molekul adalah rumit untuk molekul yang mengandung lebih dari satu atom yang mempunyai isotop berarti, misalnya C, Cl, S dan Br. Intensitas relatif puncak di daerah ion molekul untuk molekul-molekul tersebut dapat dihitung dari pernyataan:

(a + b)m

dimana a = kelimpahan relatif isotop yang lebih ringanb = kelimpahan relatif isotop yang lebih berat

m= jumlah atom unsur yang ada dalam molekul

Jadi pada senyawa yang mengandung tiga atom klor, intensitas relatif yang diberikan isotop klor adalah:(a + b)3

= a3 + 3a2b + 3ab2 + b3= 33 + 3 x 32 x 1 + 3 x 3 x 12 + 13= 27 + 27 + 9 + 1

M : M+2 : M+4 : M+627 : 27 : 9 : 1

143

Molekul dengan lebih dari satu atom yang memiliki isotop

Kombinasi isotop C12, C13, Cl35 dan Cl37 yang mungkin untuk kloroform:

C12 Cl35 Cl35 Cl35 M

C13 Cl35 Cl35 Cl35 M+1

C12 Cl37 Cl35 Cl35 M+2

C13 Cl37 Cl35 Cl35 M+3

C12 Cl37 Cl37 Cl35 M+4

C13 Cl37 Cl37 Cl35 M+5

C12 Cl37 Cl37 Cl37 M+6

C13 Cl37 Cl37 Cl37 M+7

144

m/z Intensity

35.0 4.7 36.0 1.5 37.0 1.5 47.0 19.7 48.0 9.4 49.0 6.7 50.0 3.1 82.0 3.4 83.0 100.0 84.0 3.1 85.0 65.4 86.0 1.0 87.0 10.7 117.0 1.3 118.0 2.6 119.0 1.3 120.0 2.2

Compound Name:Chloroform

Molecular Formula: CHCl3

Molecular Weight: 119.4 (Mass of molecular ion: 118)

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