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Fourier Transform Infrared (FT-IR) Spectroscopy

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Learning objectives

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After completing this course, the student will be able to:

Recognize the concept and principle of FT-IR Spectroscopy

Utilize FT-IR spectroscopy in structural, qualitative and

quantitative analysis of drug molecules

Justify types of IR spectra

Fundamental rule for FT-IR

Recognize the concept of dipole moment, principle and

applications

Advantage and disadvantage of FT-IR spectroscopy

Application of FT-IR spectroscopy

Analysis with examples for the determination of pharmaceutical

drugs.

Learning outcomes

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4

Organic Chemistry by John McMurry Page Number 408-434;

434-467; 482-503

Spectroscopic methods in Organic Chemistry, Page Number 1-

33; 35-73; 74-145; 149-195

Spectroscopy of Organic Compounds by P.S. Kalsi, page 20-450

Fundamentals of Fourier Transform Infrared Spectroscopy by Brian C. Smith; Page Number 25-145

References

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Fourier Transform Infrared (FT-IR) Spectroscopy

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Infrared (IR) spectroscopy

Measures the bond vibration frequencies in a molecule and

is used to determine the functional group

Mass spectrometry (MS)

Fragments the molecule and measures the masses

Nuclear magnetic resonance (NMR) spectroscopy

Detects signals from hydrogen atoms and can be used to

distinguish isomers

Ultraviolet (UV) spectroscopy

Uses electron transitions to determine bonding patterns

Types of Spectroscopy

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Spectroscopy is an analytical technique which helps to

determine the structure.

It destroys little or no sample

The amount of light absorbed by the sample is

measured as wavelength is varied.

Introduction

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THE ELECTROMAGNETIC SPECTRUM

INFRARED GAMMA RAYS X RAYS UV VISIBLE

Fourier Transform Infrared (FT-IR) Spectroscopy

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Infrared radiation lies between the visible

and microwave portions of the

electromagnetic spectrum.

Infrared waves have wavelengths longer

than visible and shorter than microwaves,

and have frequencies which are lower than

visible and higher than microwaves.

What is Infrared?

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Humans, at normal body temperature, radiate most

strongly in the infrared, at a wavelength of about 10

microns (A micron is the term commonly used in

astronomy for a micrometer or one millionth of a

meter). In the image to the left, the red areas are

the warmest, followed by yellow, green and blue

(coolest).

The image to the right shows a cat in the infrared.

The yellow-white areas are the warmest and the

purple areas are the coldest. This image gives us a

different view of a familiar animal as well as

information that we could not get from a visible

light picture. Notice the cold nose and the heat

from the cat's eyes, mouth and ears.

What is Infrared?

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The Infrared (IR) region is divided into three regions

1. Near region

2. Mid region

3. Far region

Near-infrared refers to the part of the infrared spectrum

that is closest to visible light.

Far-infrared refers to the part that is closer to the

microwave region.

Mid-infrared is the region between these two.

Types of IR spectra

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The primary source of infrared radiation is thermal

radiation. (heat)

It is the radiation produced by the motion of atoms and

molecules in an object.

The higher the temperature, the more the atoms and

molecules move and the more infrared radiation they

produce.

Any object radiates in the infrared. Even an ice cube,

emits infrared.

SOURCE OF IR SPETROSCOPY

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Types of Electromagnetic Radiation

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Near region : Above 4000 cm-1

Almost entirely harmonic peaks of normal frequency

Samples containing moisture can also be measure

Introduced in the fields of processed foods and agriculture

Mid region : 4000 to 400 cm-1

Produced information on molecular vibration and rotation

Far region : Below 400 cm-1

Molecular rotation information

Metal oxides, metal compounds,, organic and inorganic metal complexes.

IR REGION

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Molecular Effects Spectroscopic Methods Energy

Ionization - > 104 kcal/mol

Electronic Transitions UV-Vis 40-300 kcal/mol

Molecular Vibrations Infra-red (IR) 1-10 kcal/mol

Molecular Rotations Microwave ~ 1 kcal/mol

Nuclear Spin Transitions

Nuclear Magnetic Resonance (NMR)

10 -5 kcal/mol

Spectroscopic Methods and Quantized Transitions

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Principles

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Fundamental Equation

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IR Absorption spectroscopy

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Method Abbrev. Energy used Units

Ultraviolet-Visible Spectroscopy

UV-Vis Ultraviolet-visible

nm

Infrared Spectroscopy IR Infrared mm or cm-1

Nuclear Magnetic Resonance

NMR Radio frequencies

Hz

Mass Spectroscopy MS Electron volts

amu

The four most common spectroscopic methods used in organic analysis are:

Common methods for Drugs analysis

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Matter/Energy Interactions

What happens when a sample absorbs UV/Vis energy?

Mo

mentarily

Excitation of ground state electrons (typically p and n electrons) E electronic increases momentarily

UV/Vis

(200 nm)

sample p p* transition

p

p*

What happens when a sample absorbs IR energy?

Stretching and bending of bonds (typically covalent bonds) E vibration increases momentarily -O-H

IR

(3500 cm-1)

-O —H

What actually happens to the sample during an analysis?{How do the sample and energy interact}

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Infrared absorption occurs among the ground vibrational states.

The energy differences, and corresponding spectrum, determined by the specific molecular vibration(s).

The infrared absorption is a net energy gain for the molecule and recorded as an energy loss for the analysis beam.

hn

Excited

states

Ground

(vibrationa

l) states

h(n1 -

n0 )

h(n1 -

n0)

h(n2 - n1)

(overtone)

Infrared Absorption and

Emission

n1

n2

n0

n3

Energy levels in Infrared Absorption

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A dipole moment is a measurement of the separation of two oppositely charged particles

Absorption strength depends on the size of deformation of the dipole moment due to vibration

Dipole Moment

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Infrared light and a molecule only interact when the dipole

moment of the molecule changes due to vibration

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Infrared Spectroscopy

The bonds between atoms in the molecule stretch and bend,

absorbing infrared energy and creating the infrared

spectrum.

Symmetric Stretch Antisymmetric Stretch Bend

A molecule such as H2O will absorb infrared light when the

vibration (stretch or bend) results in a molecular dipole

moment change

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Which of the following atoms or molecules will

absorb IR radiation:

H—Cl H2 N2 Cl2

Why?

Example

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The number of normal frequencies of a molecules consisting of n atoms can be determined by the following formula:

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A molecule can be characterized (identified) by its molecular vibrations, based

on the absorption and intensity of specific infrared wavelengths.

Infrared Spectroscopy (Water Molecule)

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Infrared Spectroscopy

For isopropyl alcohol, CH(CH3)2OH, the infrared absorption bands identify

the various functional groups of the molecule

Infrared Spectroscopy (Isopropyl alcohol)

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Absorption position

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Absorption position

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Finger print region

The region below 1500 cm-1 is rich in many absorptions which

are caused by bending vibrations.

In the spectrum, the number of bending vibrations is usually

more than the number of stretching vibrations.

This regions is called Finger print region. Some substances

containing the same functional group show similar absorptions

above 1500 cm-1 but their absorption position differ in the

finger print region.

Such compounds can be easily distinguished by comparing their

finger print regions.

Infrared spectroscopy (IR) measures the bond vibration

frequencies in a molecule and is used to determine the functional

group

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IR Correlation Diagram Tra

nsmitta

nce (%)

100

80

60

40

20

0

4000 3500 3000 2500 2000 1500 1000

2.5 3.0 4.0 5.0 6.0 10.0

Frequency (cm-1)

Region I

3600-2700 cm-1

Region II

1800-1600 cm-1

/ Wavelength (microns, mm)

O-H N-H C-H bond stretching

Alcohols Phenols Carboxylic acids

Amines Amides

Alkynes Alkenes Alkanes

C=O

Acid chlorides Anhydrides

Esters Ketones

Aldehydes Carboxylic acids

Amides

Fingerprint Region

(below 1500 cm-1)

C-H =C-H -C-H

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Functional Group

Type Frequencies cm-1

Peak Intensity

C-H sp3 hybridized R3C-H 2850-3000 M(sh)

sp2 hybridized =CR-H 3000-3250 M(sh)

sp hybridized C-H 3300 M-S(sh)

aldehyde C-H H-(C=O)R 2750, 2850 M(sh)

N-H primary amine, amide RN-H2, RCON-H2 3300, 3340 S,S (br)

secondary amine, amide RNR-H, RCON-HR 3300-3500 S (br)

O-H alcohols, phenols free O-H 3400-3580 W(sh)

hydrogen bonded 3600-3650 S(br)

carboxylic acids R(C=O)O-H 3500-2400 S(br)

CN nitriles RCN 2280-2200 S(sh)

CC acetylenes R-CC-R 2260-2180 W(sh)

R-CC-H 2160-2100 M(sh)

C=O aldehydes R(C=O)H 1740-1720 S(sh)

ketones R(C=O)R 1730-1710 S(sh)

esters R(CO2)R 1750-1735 S(sh)

anhydrides R(CO2CO)R 1820, 1750 S, S(sh)

carboxylates R(CO2)H 1600, 1400 S,S(sh)

C=C olefins R2C=CR2 1680-1640 W(sh)

R2C=CH2 1600-1675 M(sh)

R2C=C(OR)R 1600-1630 S(sh)

-NO2 nitro groups RNO2 1550, 1370 S,S(sh)

A summary of the principle infrared bands and their assignments. R is an aliphatic group.

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Analysis Targets

Compound: Organic and Inorganic compounds

State: Gas, Solid and Liquid

Analysis description

Qualitative analysis

Functional group analysis : How many function groups present in the compounds with respect to the data

Pattern analysis: What is the materials by comparing standard spectra

Quantitative analysis

From the absorption we can determine the concentration

Finger print preparation

Quantitative analysis

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Types of Transmission Technique

Solid samples

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Liquid samples

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KBr Pellet Technique

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KBr Pellet Technique

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BRUKE TENSORTM

Series

Perkin ElmerTM Spectrum One

Instrumentation

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Thin film Technique

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Real Chromatogram for liquid samples

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Gas cell

Gas cell

The gaseous samples are imported because one can in some cases see also the rotational fine structure of the absorption bands. The sample gas is placed in a gas cell at low temperature and pressure

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Real Chromatogram of Gas sample

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Diagram of IR spectroscopy

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FTIR seminar

Interferometer

He-Ne gas laser

Fixed mirror

Movable mirror

Sample chamber

Light

source

(ceramic)

Detector

(DLATGS)

Beam splitter

FT Optical System Diagram

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Fixed mirror Ｂ Movable mirror

Fixed mirror Ａ Movable mirror

Fixed mirror Ｃ Movable mirror

Same-phase interference wave shape

Opposite-phase interference wave shape

Same-phase interference wave shape l 0

Movable mirror

Ｄ Interference pattern of light manifested by the optical-path difference

Continuous phase shift

Signa

l st

reng

th

Ｉ (X)

-2l -l 0 l 2l

-2l -l 0 l 2l

Interference of two beams of light

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Relationship between light source spectrum and the signal output from interferometer

(a) Monochromatic light (b) Dichroic light (c) Continuous spectrum light

All intensities are standardized.

Light source spectrum Signal output from interference wave

Time t

Time t

Time t I(t)

I

b (u)

Wavenumber u

Wavenumber u

Wavenumber u

S I

SAz

Az

Interference is a super positioning of waves

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1. Better sensitivity and brightness - Allows simultaneous measurement over the entire wavenumber range - Requires no slit device, making good use of the available beam

2. High wavenumber accuracy

- Technique allows high speed sampling with the aid of laser light interference fringes - Requires no wavenumber correction - Provides wavenumber to an accuracy of 0.01 cm-1

3. Resolution

- Provides spectra of high resolution

4. Stray light - Fourier Transform allows only interference signals to contribute to spectrum. - Background light effects greatly lowers. - Allows selective handling of signals limiting intreference

5. Wavenumber range flexibility - Simple to alter the instrument wavenumber range

CO2 and H2O sensitive

FT-IR Advantages

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Identification and quantitation of organic solid, liquid or gas

samples.

Analysis of powders, solids, gels, emulsions, pastes, pure

liquids and solutions, polymers, pure and mixed gases.

Infrared used for research, methods development, quality

control and quality assurance applications.

Samples range in size from single fibers only 20 microns in

length to atmospheric pollution studies involving large areas.

Capabilities of Infrared Analysis

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Pharmaceutical research

Forensic investigations

Polymer analysis

Lubricant formulation and fuel additives

Foods research

Quality assurance and control

Environmental and water quality analysis methods

Biochemical and biomedical research

Coatings and surfactants

Etc.

Applications of Infrared Analysis

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Which is the following compounds a-d has an IR absorption at 3400 cm-1?

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A strong absorption signal at 1650 cm-1 in an IR spectrum indicates the presence of

b.

C. a

What is the structure of the compound that gives the following IR spectrum?

a. CH3-CH2-CC-H b. CH3-CH2-OH c. CH3-CH2-CC-H d. CH3-CH2-CH2-NH2

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A strong absorption signal at 3400 cm-1 in an IR spectrum indicates the presence of

a. CH3CH2OH b. (CH3)2CHCN c. CH3CH2OCH2OCH2CH

b. CH3CH2CH=O a. CH3OH

What is the structure of the compound that gives the following IR spectrum?

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The molecular formula C8H11O that is consistent with the IR spectrum below is

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The structure of the compound that gives the infrared (IR) spectrum below is

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10

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95%

T

500 1000 1500 2000 2500 3000 3500 4000

Wav enumbers (cm-1)

2900 cm-1

1710 cm-1

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%T

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3450 cm-1 2970 cm-1

1470 cm-1

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2950 cm-1

1480 cm-1

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2990 1710

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2999 1700

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C-O 10

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3540

3020

1750

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F

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G

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Why water cannot be used as solvent in IR spectroscopy?

Water is IR active so produces a peak due to it OH group at 3500cm-1 this

is why equipment should be keep in oven

Why KBr is used to prepare the IR samples.

What is the difference of UV and IR

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Deduce the structure of an unknown compound with molecular formula

C5H12O using information given by its infrared spectrum.

Intensity (peak): Frequency (cm–1):

s 3300

d 2800

t 2700

s 1465

s 1450

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Deduce the structure of an unknown compound with molecular

formula C9H10O using information given by its infrared

spectrum.

Intensity (peak): Frequency (cm–1):

s 2900

m 2800

s 1600

m 1475