qfl-4030 métodos espectroscópicos de análise (2014) home page: (courses)
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QFL-4030 Métodos espectroscópicos de análise (2014)
Home Page: http://www2.iq.usp.br/docente/majokato (courses)
Literatura
Silverstein, R. M., Webster, F. X. and Kiemle, D. J. (2005) Spectrometric identification of organic compounds, 7th ed. J. Wiley & Sons.
Pavia, D. L., Lampman, G. M., Kriz, G. S. (1996). Introduction to spectroscopy. 2nd ed. Saunders College Publishing.
Modern Instrumental Techniques for Schools and CollegesRoyal Society of Chemistry – Advancing the Chemical Sciences:https://www.youtube.com/watch?v=DDTIJgIh86E
Objetivos
Apresentar os fundamentos básicos e as
aplicações dos principais métodos
espectroscópicos utilizados em análise química
estrutural, de modo a capacitar os alunos a
interpretar espectros.
Programa
Espectroscopia no UV-vis,
infravermelho (IV),
espectrometria de massas e
ressonância magnética nuclear.
Discovery of organic compounds was primarily motivated by bioactivity and their structural determination was based mostly
on degradative reactions
• Morfina: Sertürner, 1805• Quinina: Pelletier e Magendie, 1820• Atropina: Mein, 1831.• Papaverina: Merck, 1848.• Cocaína: Wöhler, 1859.• Escopolamina: Landenburg, 1881. • Efedrina: Nagai, 1885.• Tubocurarina: Boehm , 1895.• Insulina: Abel, 1929.
• Penicilina: Fleming, 1929.• Dicumarol: Link, 1941.• Cloranfenicol: Burkholder, 1947.• Reserpina: Müller, 1952.• Prostaglandinas: Bergströn, 1962.• Encefalinas: Hughes, 1975.
quinina
N
NHO
MeO
Uso como antimalárico: Desde 1638
Isolamento: 1820 por Pelletier e Caventou
Síntese: 1944 por Woodward
Determinação estrutural da quinina porreações de degradação
quiteninaquinina
KMnO4
N
N
CO2H
HO
MeO
N
NHO
MeO
meroquinenoácido
quinínico
+NO
OHCrO3 N
CO2HMeO
N
NMeO
O
ac. cincoloipônico
N
CO2H
HO2C
NOOH
meroquineno
N
CNCH(CO2Et)2
N
CN
-cloropropionacetal
-cloropropional
ClCH2CH2CHO
NH3
CH(OEt)2
ClCl
CH(OEt)2
Confirmadas por síntese dos fragmentos obtidos
N
NHH2N
CH3OPrimaquineIs used to treat malaria caused by P. vivax and P. ovale. It should be used in association with chloroquine or mefloquine to provide a complete cure. It is also used to treat fungal infections caused by Pneumocystis pneumonia, common in patients with AIDS.
N
NHO
CF3
Mefloquine (Lariam, Mefaquin)This quinine analog developed at Walter Reed Army Institute of Research (USA) and was used for the prophylaxis of malaria and also for treatment of chloroquine-resistant falciparum type.
N
MeO
HO NQuinine (natural antimalarial compound)
Cinchona officinalis (quinine bark - Rubiaceae)
Synthetic derivatives:
Como diferenciar uma molécula de outra?
N
NHO
CF3
HO
H
• Massa: EM• Composição (tipos e quantidade de átomos): AE• Rotação: Micro-ondas• Vibração: Infravermelho• Orbitais moleculares: UV-Vis • Organização em cristais: Difração de raios X• Estados de spin (mediante campo magnético): RMN
Ponto de fusão, índice de refração, forma, tamanho, etc…
Análise elementar – Determinação fórmula mínima
CxHyOz + O2 (excesso) = x CO2 + y/2 H2O
9.83 mg 23.26 mg 9.52 mg
CxHyOz, x = 64.6%; y = 10.8%; z = 24.6% C7H14O2
Fórmula mínima
Eletronictransitions
Bond breaking
Nuclear spintransitions
Vibrationaltransitions
EM UV-VIS IV RMN
frequency
energy
http://upload.wikimedia.org/wikipedia/commons/thumb/d/d9/Espectro_Eletromagn%C3%A9tico.png/700px-Espectro_Eletromagn%C3%A9tico.png
Comparação do comprimento de onda
Plant tissue,microorganism
and etc
Extraction bystem distillation,organic solvent
or CO2
Fractionation and purification
(solvent extractions,column chromatography,
HSCC, etc)
Purecompound
Determination ofmolecular formula
(elemental analysisor HRMS)
Determination offunctional groups
(IR, UV, 1H and 13C NMR)
Determination of types of carbons(CH3, CH2, CH, C)and sub-structures
(1H NMR: multiplicities and integration; 13C NMR: chemical shifts and DEPT 135)
Determination ofconnectivities and planar
structures (J3 1H-1H;13C NMR: HSQC; HMBC)
Determination oftridimensional structuresor spatial relationships
(J3 1H-1H;13C NMR: NOESY, TOCSY)
Determination ofabsolute configuration
(optical rotation, circular dichroisms and R-X)
Chromatographicprofile, melting point,
boiling point, refraction index, etc)
General scheme for structural elucidation of natural compounds
𝐼=𝐶−𝐻2−𝑋2+𝑁2+1=2
C-O
OH
MM = 70 u.a.
CH2 OH
CxHyOz C4H6O
CH2 CH
-18 (OH)
C-H
C-HCC
HC C CH2 CH2 OH
Análise funcional orgânica
Espectrofotometria no Ultravioleta e
infravermelho
Determinação de grupos funcionais:
Infrared radiation
λ = 2.5 to 17 μm
n (número de onda) = 4000 to 600 cm-1
These frequencies match the frequencies of covalent bond stretching and bending vibrations.
Infrared spectroscopy can be used to find out about covalent bonds in molecules.
IR is used to tell:
1. what type of bonds are present
2. some structural information
Infrared
10,000 cm-1 to 100 cm-1
Converted in Vibrational energy in molecules
Vibrational Spectra appears as bands instead of sharp lines => as it is accompanied by a number of rotational changes
Wave Number => n (cm-1) => proportional to energy
n Depends on:
• Relative masses of atoms• Force constant of bonds• Geometry of atoms
Older system uses the wavelenght l (mm => 10-6 m)
cm-1 = 104 / mm
Lei de Hooke
Instrumentação
IR source è sample è prism è detector
graph of % transmission vs. frequency
=> IR spectrum
4000 3000 2000 1500 1000 500
v (cm-1)
100
%T
0
Intensity: Transmittance (T) or %T
T =II0
Absorbance (A)
A = log II0
Intensity in IR
IR : Plot of %IR that passes through a sample (transmittance) vs Wavelenght
Instrumentação
Espectro no IV
Infrared
• Position, Intensity and Shape of bands gives clues on Structure of molecules
• Modern IR uses Michelson Interferometer=> involves computer, and Fourier Transform (FTIR)
Sampling => plates, polished windows, Films …Must be transparent in IR
NaCl, KCl : Cheap, easy to polish
NaCl transparent to 4000 - 650 cm-1
KCl transparent to 4000 - 500 cm-1
KBr transparent to 400 cm-1
Infrared: Low frequency spectra of window materials
Transmission of different window materials: CsI, CsBr, KBr, NaCl, CaF2 and Ge; Thickness: Ge 3 mm, CsBr 4mm, all others 5mm
How to prepare samples IR Spectroscopy and how to take an IR spectrum.
https://www.youtube.com/watch?v=FfI5BczOXQ8
IR-Absorption by Solvents
Most solvents are of little use for IR spectroscopy because they block most of the of the typical spectral range range (4000 - 600 cm-1).
A few notable exceptions are CS2, CHCl3 and CCl4
A complete solution spectrum of a compound can usually be assembled by measuring in CS2 and CHCl3.
CCl4
http://fy.chalmers.se/OLDUSERS/brodin/MolecularMotions/CCl4modes.html
Vibrationswww.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm
Modes of vibration
C—HStretchingBending C
OH
H
H
Symmetrical 2853 cm-1
H
H
Asymmetrical 2926 cm-1
H
H
H
H
Scissoring1450 cm-1
Rocking720 cm-1
HH
HH
Wagging1350 cm-1
Twisting1250 cm-1
Stretchingfrequency
Bendingfrequency
Modos vibracionais
http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Vibrational_Modes
Vibrationswww.cem.msu.edu/~reusch/Virtual/Text/Spectrpy/InfraRed/infrared.htm
General trends:•Stretching frequencies are higher than bending frequencies (it is easier to bend a bond than stretching or compresing them)
•Bond involving Hydrogen are higher in freq. than with heavier atoms
•Triple bond have higher freq than double bond which has higher freq than single bond
Symmetrical and asymmetrical stretch
Methyl 2872 cm-1
Symmetrical Stretch Asymmetrical Stretch
—C—H
H
H
—C—HH
H
Anhydride
O
O O1760 cm-1
2962 cm-1
1800 cm-1
O
O O
Amino
Nitro
—NH
H3300 cm-1 3400 cm-1
1350 cm-1 1550 cm-1
—NH
H
—N
O
O—N
O
O
EstiramentosOu deformações axiais
IR spectra of ALKANESC—H bond “saturated”
(sp3) 2850-2960 cm-1
+ 1350-1470 cm-1
-CH2- + 1430-1470
-CH3 + “ and 1375
-CH(CH3)2 + “ and 1370, 1385
-C(CH3)3 + “ and 1370(s), 1395 (m)
n-pentane
CH3CH2CH2CH2CH3
3000 cm-1
1470 &1375 cm-1
2850-2960 cm-1
sat’d C-H
CH3CH2CH2CH2CH2CH3
n-hexane
cyclohexane
no 1375 cm-1
no –CH3
IR of ALKENES=C—H bond, “unsaturated” vinyl
(sp2) 3020-3080 cm-1
+ 675-1000
RCH=CH2 + 910-920 & 990-1000
R2C=CH2 + 880-900
cis-RCH=CHR + 675-730 (v)
trans-RCH=CHR + 965-975
C=C bond 1640-1680 cm-1 (v)
Bond length and strength vs
Stretching frequency
Bond C-H =C-H -C-H
Length 1.08 1.10 1.12
Strenght 506 kJ 444 kJ 422 kJ
IR freq. 3300 cm-1 3100 cm-1 2900 cm-1
1-decene
910-920 & 990-1000 RCH=CH2
C=C 1640-1680
unsat’dC-H
3020-3080 cm-1
Alkene
In large molecule local symmetry produce weak or absent vibration
C=C
R
Rtrans C=C isomer -> weak in IR
Observable in Raman
1665
cis-4-octene
1665
trans-4-octene
2055 cm-1
Nitrile
Other Nitrogen Compounds
Nitriles
Isocyanates
Isothiocyanates
Imines / Oximes
R-CN : Sharp 2250 cm-1
Conjugation moves to lower frequency
R-N=C=O Broad ~ 2270 cm-1
R-N=C=S 2 Broad peaks ~ 2125 cm-1
R 2C=N-R 1690 - 1640 cm-1
Como as bandas no IV são afetadas?
Eletronegatividade do carbono (C-H)Números de onda
Maiores/Frequencias maiores
C C H C C H C C H
3300 cm-1 3100 cm-1 2900 cm-1
styrene
no sat’d C-H
910-920 & 990-1000
RCH=CH2mono
1640C=C
Infrared of alcohols and amines• O–H 3400 to 3650 cm1
– Usually broad and intense• N–H 3300 to 3500 cm1
– Sharper and less intense than an O–H
Cyclohexanol
IR spectra ALCOHOLS & ETHERS
C—O bond 1050-1275 (b) cm-1
1o ROH 1050
2o ROH 1100
3o ROH 1150
ethers 1060-1150
O—H bond 3200-3640 (b)
1-butanol
CH3CH2CH2CH2-OH
C-O 1o
3200-3640 (b) O-H
2-butanol
C-O 2o
O-H
tert-butyl alcohol
C-O 3oO-H
methyl n-propyl ether
no O--H
C-O ether
Free OH and Hydrogen bonded OH
Band Shape: OH vs NH2 vs CH
Infravermelho de aminas
O
H
O
R
O
OR
O
OH
O
NH2
C C C
C C
1740-1690 cm-1 1750-1680 cm-1 1750-1735 cm-1
1780-1710 cm-1 1690-1630 cm-1
Estiramento de compostos carbonílicos
Which compound is this?a) 2-pentanoneb) 1-pentanolc) 1-bromopentaned) 2-methylpentane
1-pentanol
What is the compound?a) 1-bromopentaneb) 1-pentanolc) 2-pentanoned) 2-methylpentane
2-pentanone
Ketone and ConjugationnConjugation: Lower
Ketone and Ring Strain
nRing Strain: Higher
Factors influencing C=O
2) Ring size
O
1715 cm-1
Angle ~ 120o
CH3
CH3
O
O
1751 cm-1
< 120o
O
1775 cm-1
<< 120o
Factors influencing carbonyl: C=O 3) a substitution effect (Chlorine or other halogens)
—C—C—
X
O
Result in stronger bound higher frequency n
O
Cl 1750 cm-1
4) Hydrogen bonding Decrease C=O strenghtlower frequency
O
OCH3
OH
1680 cm-1
Factors influencing carbonyl: C=O
5) Heteroatom
Y
R
O
Inductive effectStronger bond
higher frequency
e.g. ester
Y
R
O
Resonance effectWeaker bondLower frequence
e.g. amides
Y C=O
ClBrOH (monomer)OR (Ester)
1815-17851812
17601705-1735
NH2
SR1695-1650
1720-1690
inductive
resonance
Ester Carbonyl
Esters C=O n ~ 1750 – 1735 cm-1
O-C : 1300 – 1000 2 or more bands
Conjugation => lower freq.
R OR
O
Inductive effect with O reinforce carbonyl => higher n
Conjugation with CO weaken carbonyl => Lower n
Ester carbonyl: C=O
Lactone carbonyl: C=O
Lactones Cyclic Ester
O
O
17351720 1760
17701750 1800
O
O
O
O
OO
OO O
O
Carbonyl compounds : Acids
Carboxylic acid
Exist as dimer :
CH3 C
OH
O
CH3C
OH
O
Strong Hydrogen bond
OH : Very broad 3400 – 2400 cm-1
C=O : broad 1730 – 1700 cm-1
C—O : 1320 – 1210 cm-1 Medium intensity
Carbonyl compounds : Acids
C=O
OH
C=O : 1711 cm-1
OH : Very Broad 3300 to 2500 cm-1 C-O : 1285, 1207 cm-1
Anhydrides
CH3 O
O
CH3
OC=O always has 2 bands:
1830-1800 and 1775-1740 cm-1
C—O multiple bands 1300 – 900 cm-1
Carbonyl compounds : AldehydesAldehydes C=O n ~ 1725 cm-1
O=C-H : 2 weak bands 2750, 2850 cm-1
Conjugation => lower freq.
C=O : 1724 cm-1
Carbonyl compounds : Aldehydes
IR SPECTRA: WHAT YOU CAN TELL AT A GLANCE
1) Is carbonyl group present (1820-1650 cm-1)?
Acid OH: 3400-2400 cm-1
Amides N-H: 3400 cm-1
Ester C-O: 1300-1000 cm-1
Anhydrides two bands: 1810 and 1760 cm-1
Aldehydes C-H: 2850 and 2750 cm-1
Ketones preceding 5 choices eliminated
2) If C=O is absent:
ROH OH: 3400-3300 cm-1;
or ArOH C-O near 1300-1000 cm-1
Amines N-H: 3400 cm-1)
Ether C-O: 1300-1000 cm-1; absence of OH
Double bond/aromatic ring:
C=C: weak band near 1650 cm-1;
1600-1450cm-1)
Triple bonds C=N: 2250 cm-1 (m)
C=C: 2150 cm-1 (w)
check for C-H (3300 cm-1)
Hydrocarbons 3000 cm-1;
1460 and 1375 cm-1
Intensity of C=O vs C=C
1758 cm-1
1783 cm-1
1702 cm-1
1686
1715
Massa atômica (C-X)Conjugação
Ligações de hidrogênio
Números de ondamenores
C-H3000
C-C1200
C-O1100
C-Cl750
C-Br600
C-I500
Chapter 12 96
An Amine IR Spectrum
=>
Chapter 12 97
An Amide IR Spectrum
=>
Summary of IR Absorptions