Abstract

In this experiment, we carried out an experiment which involves

Fourier Transform Infrared (FTIR) Spectroscopy. IR is used to

gather information about compound's structure, assess its purity,

and sometimes to identify it. Infrared radiation is that part of

the electromagnetic spectrum between the visible and microwave

regions. Infrared radiation is absorbed by organic molecules and

converted into energy of molecular vibration, either stretching

or bending. Different types of bonds, and thus different

functional groups, absorb infrared radiation of different

wavelengths. An IR spectrum is a plot of wavenumber (X-axis) vs

percent transmittance (Y-axis). Provided with the materials which

consist of (paraffin oil, acetophenone and toloune) liquid form

and caffeine (solid form), these samples will undergo

spectroscopy using the FTIR machine which is called Perkin Elmer

Spectrum One FTIR, which is manually conducted by using a

computer interconnected to the FTIR machine. The machine will

“scan” show the stretching and bending frequency bands of the

functional groups where the result from the machine will be

printed out. Depending on which functional group does the IR

absorption belongs to, it will show different types of

wavenumbers depending on which stretching and bending frequency

bands they are categorized at the table. By using the IR spectra

of the known compound, we will find out what is the unknown

compound where we are going to compare the stretching and bending

frequency bands of the functional groups. Through this experiment

result it is proven that the unknown sample is Ethanol.

Hypothesis

The unknown sample is from alcohol group which is ethanol and it

is not oleic acid.

Experimental Procedure

The instrument was calibrated using a standard polystyrene film

and the sample was prepared and the spectrum of each compound was

obtained and recorded.

Procedure

A. Liquid sample

Two salt plates were rinsed using chloroform and wiped dry. A

sample of liquid Paraffin was taken and one drop of liquid

Paraffin was added onto one of the salt plates. The liquid was

squeezed between two salt plates to give a layer that has a

thickness of 0.01mm or less. The two plates, held together by

capillary action were then mounted in the beam path of the

spectrophotometer. The results were printed as a graph. The steps

above were repeated for another two more samples which are

acetophenone and toluene.

B. Potassium bromide, KBr pellets for solid sample

Figure 1: KBr handpress

Approximately 1mg of Caffeine solid sample was ground until they

form fine powder. A few milligrams of KBr were added and the

mixture was ground again where the ratio needs to be in the form

of 1:9. To make the KBr pellet, the die pin from the storage

container, as shown in figure 1, was removed. The collar was

placed on the lower anvil. Powdered KBr was then placed in the

collar until all the surface of the lower anvil was covered

evenly. After that, the upper anvil was placed so that it came

into contact with the sample. The hand press was held in upright

position. The handle was lifted and the pressure dial at the top

of the press was rotated counter clockwise one revolution from

full clockwise position. The die set was then carefully placed in

the hand press. To close the handle, the pressure dial was

rotated clockwise until the upper ram of the handpress touched

the upper anvil of the die assembly. The handle was opened and

the dial was rotated clockwise three to five times. After about

20 seconds, open the KBr handpress and the pellet infrared

spectrum were measured. Afterwards, the pellet was removed from

the collar and the entire die set was stored back into the

desiccator.

Results

Parafilm Calibration

Calibration Test/cm-1 Calibrated TRM/cm-1

3082.29 3082.22(±0.5)

3060.25 3059.95(±0.5)

1601.51 1601.36(±0.5)

1583.19 1583.20(±0.5)

1028.58 1028.44(±0.5)

Paraffin oil (CnH (2n+2))

Functional

Group

Molecular

Motion

Wavenumber (cm-

1)

Experiment

Wavenumber

(cm-1)

Alkanes

C-H stretch 2950-2800 2924.14

CH2 bend Approx. 1465 1463.64

CH3 bend Approx. 1375 1377.70

CH2 bend(4 or

more)

Approx. 720 722.21

Toluene ( C 6H5CH3)

Functional

Group

Molecular

Motion

Wavenumber (cm-1) Experiment

Wavenumber

(cm-1)

Aromatics

C-H stretch 3020-3000 2955.83

C=C stretch Approx. 1600 &

1475

1604.66 &

1495.83

C-H

bend(mono)

770-730 & 715-

685

728.40

Acetophenone (C6H5C(O)CH3)

Functional

Group

Molecular

Motion

Wavenumber (cm-1) Experiment

Wavenumber

(cm-1)

Ketones

C=O stretch Approx. 1715 1684.08

C-C stretch 1300-1100 1266.31

Aromatics

C-H stretch 3020-3000 3065.76

C=C stretch Approx. 1600 &

1475

1599.10

C-H

bend(mono)

770-730 & 715-

685

759.75

Caffeine

Functional

Group

Molecular Motion Wavenumber (cm-

1)

Experiment

Wavenumber

(cm-1)

Aromatics C=C stretch Approx. 1600 & 1483.01

1475

Amines

C-N stretch

(alkyl)

1200-1025 1025.00

C-N stretch

(aryl)

1360-1250 1358.65 &

1285.46

Amides

C=O stretch 1680-1630 1655.10

N-H stretch 3500-3180 3111.89

Unknown Sample

Functional

Group

Molecular

Motion

Wavenumber (cm-

1)

Experiment

Wavenumber

(cm-1)

Alcohol

O-H stretch Approx. 3650 or

3400-3300

3399.42

C-O stretch 1260-1000 1087.90 &

1047.67

Alkane C-H stretch 2950-2800 2976.88

Discussion

Before performing the experiment, a background check was done onthe FTIR machine to ensure that the machine is in a goodcondition by running a blank spectrum. The machine was calibratedusing a standard polystyrene film which the calibrated marks aregiven. By comparing the IR spectra it is observed that themachine was properly calibrated and it is in its tip topcondition. Next, to determine the compound of unknown 1, theimportant bending and stretching frequency of the functionalgroup was studied and compared to the IR absorptions forRepresentative Functional Groups Infrared Spectroscopy. It wasfound that there is a stretching point where O-H was stretched at3399.42 cm-1 and C-O was stretched at 1087.90 cm-1 and 1047.67 cm-1.The unknown compounds are between ethanol and oleic acid. When wesearch for the functional group of oleic acid it shows that therewas not any spectrum that reflected carboxylic acid functionalgroup was present, it can be concluded that ethanol is theunknown 1 compound. However, to know for sure that the compoundis an alcohol, the second strong stretch of the spectrum wasstudied. Absorbed at the wavenumber 2976.55cm−1, the molecularmotion was identified as the C−H stretch. From the IR Absorptionsfor Representative Functional groups table, it can be stated thatthe compound comes from the alkane group, which possesses singlebond in its compound. There was another stretching frequency bandwas identified from the graph. That would be the C−O stretcheswith the wavenumbers of 1087.90cm−1 and 1047.67cm−1. From thedata, it can be concluded that the unknown is ethanol.

Conclusion

Based on the IR spectrum graph given, my conclusion is that theunknown sample is identified as ethanol. This conclusion ispurely based on the observation and the data from the stretching

frequency bands in the graph, where the absorbed wavenumbersshowed the presence of alcohol and alkane functional groups.

Reference

1. <IR Absorptions Table for Representative Functional Groups>

http://www.instruction.greenriver.edu/kmarr/chem%20162/Chem1

62%20Labs/Interpreting%20IR%20Spectra/IR%20Absorptions%20for

%20Functional%20Groups.htm

2. D. L. Pavia, G. M. Lampman, G. S. Kriz, J. R Vyvyan (2001).

Introduction to Spectroscopy, Fourth Edition. USA;

Department of Chemistry Western Washington.

Experiment 1

Fourier Transform Infrared (FTIR) Spectroscopy

Prepared byChurchill Nyalong Anak David Kennedy

2012995615AS229 2C

Prepared forPn. Zarila Mohd. Shariff

Group members1. Nursabrina Binti Samsudin2. Muhammad Hazim Bin Zahid

Date of experiment performed19th September 2013

Date of submission26th September 2013