Aim

To record and interpret the infrared (IR) spectrum of ethyl alcohol and identify the characteristic functional group absorption bands.

Principle

Infrared spectroscopy is used to identify functional groups in organic compounds. When infrared radiation passes through a molecule, certain wavelengths are absorbed due to vibrational transitions of chemical bonds.

Each functional group absorbs IR radiation at a characteristic wavenumber (cm⁻¹). By analyzing the peaks in the IR spectrum, the structure of the compound can be interpreted.

Apparatus

FTIR spectrophotometer
IR sample holder or KBr cell

Chemicals

Ethyl alcohol (ethanol)

Procedure

Place a small amount of ethyl alcohol in the sample holder of the FTIR spectrophotometer.
Run the instrument and record the IR spectrum in the range 4000–400 cm⁻¹.
Note the important absorption peaks from the spectrum.
Assign the peaks to the corresponding functional groups.

Observation Table

Sr. No.	Wavenumber (cm⁻¹)	Type of Vibration	Functional Group
1	3200–3600	O–H stretching (broad)	Alcohol
2	2850–3000	C–H stretching	Alkane
3	1450	C–H bending	Alkane
4	1050–1100	C–O stretching	Alcohol
5	650–800	O–H bending	Alcohol

Interpretation of Spectrum

A broad strong peak around 3200–3600 cm⁻¹ indicates the presence of O–H stretching, characteristic of alcohols.
Peaks around 2850–3000 cm⁻¹ correspond to C–H stretching vibrations of alkyl groups.
A strong band near 1050–1100 cm⁻¹ confirms C–O stretching, which is typical for primary alcohols.
Bending vibrations around 1450 cm⁻¹ indicate the presence of C–H groups.

Result

The IR spectrum of ethyl alcohol shows characteristic peaks of O–H, C–H, and C–O functional groups, confirming the presence of a primary alcohol structure.