-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
1/33
Introduction to
SpectroscopyInfrared Spectroscopy
CHM 243 Organic Chemistry I
Dr. Frank Yepez CastilloMisericordia University
Fall 2013
1
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
2/33
Introduction to Spectroscopy
Organic chemists use several spectroscopictechniques to determine the structure of acompound
Most techniques are nondestructive.
All of the spectrometric techniques rely on the
interaction of matter (your sample) and differentsources of energy
2
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
3/33
Light has wave-like and particle-like properties
3
The frequency of a wave is the
number of complete cyclesthat pass a fixed point in asecond
Wavelength is the distance betweenany two peaks (or any two troughs) ofthe wave
Energy Sources: Light (Electromagnetic
radiation)
=c
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
4/33
Light has wave-like and particle-like properties When viewed as a particle, electromagnetic radiationconsists of packets of energy, called photons.The energy of each photon is directly proportional to itsfrequency.
h is Plancks constant (6.62 x 10-37 kJ.s)
4
Energy Sources: Light (Electromagnetic
radiation)
E= h
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
5/33
Energy Sources: Light (Electromagnetic
radiation) and
These two equations can be combined into thefollowing:
High frequencies and short wavelengths areassociated with high energy
5
E= h =c
E=hc
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
6/33
Spectroscopy
Spectroscopy involves an interaction between matter andlight (electromagnetic radiation).
6
IR region ranges from 10,000 100 cm-1
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
7/33
Types of Spectroscopy
7
Different regions of the electromagnetic spectrum are usedto probe different aspects of molecular structure
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
8/33
Molecules can store energy in a variety of ways: Rotational motion Bond vibrations Electronic transitions
8
All these forms or energy are quantized
Electromagnetic radiation
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
9/33
The IR Region
9
From right below the visible region to just above thehighest microwave and radar frequencies
Wavelengths are usually 2.5 x 10-4 to 25 x 10-4 cm More common units are wavenumbers (), or cm-1, the
reciprocal of the wavelength in centimeters Wavenumbers are proportional to frequency and energy
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
10/33
The IR Region
10
The IR region that is of particular interest to organicchemists is the limited portion between 4000 cm-1 and400 cm-1
Absorption in the IR region corresponds to energychanges in the order of 8 to 40 kJ/mol.
These energy levels encompass the stretching andbending vibrational frequencies of the bonds in mostcovalent molecules.
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
11/33
IR SpectrumIntensity of the signals are normally expressed as either transmittance (T) orabsorbance (A)
Transmittance is the ratio of the radiant power transmitted by a sample to theradiant power incident on the sampleAbsorbance is the logarithm, to the base 10, of the reciprocal of thetransmittance:
Each signal on the IR spectrum has three important characteristics:wavenumber, intensity, and shape
11
A = log10(1T)
-
7/27/2019 Introduction to Spectroscopy: Infrared Spectroscopy
12/33
IR SpectrumPeaks in the IR correspond to a particular kind of bond, and each bond type(such as O-H and C-H) occurs at a characteristic frequency
The IR spectrum is divided into two regions: a) The functional group region ( 1500 cm-1)b)
The fingerprint region (