Exercise 4 : - Infrared spectra

1. The IR spectrum of a compound of molecular formula C₁₁H₈O is given below:

a. Calculate the degree of unsaturation indicated by the molecular formula.

(2 x 11 – 8 + 2)/2 = 8

b. Using the molecular formula, list all possible functional groups.

alcohol, aldehyde, ether, ketone

c. Identify the functional group.

aldehyde

2. The IR spectrum of a compound of molecular formula C₆H₁₅N is given below:

a. Calculate the degree of unsaturation indicated by the molecular formula.

(2 x 6 + 1 – 15 + 2)/2 = 0

b. Using the molecular formula, list all possible functional groups.

1^o, 2^o or 3^o amine

c. Identify the functional group.

primary amine

3. The IR spectrum of a compound of molecular formula C₁₀H₁₂O₂ is given below:

a. Calculate the degree of unsaturation indicated by the molecular formula.

(2 x 10 – 12 + 2)/2 = 5

b. Using the molecular formula, list all possible functional groups.

alcohol, aldehyde, carboxylic acid, ester, ether, ketone,

c. Identify the two functional groups.

ketone and ether

4. The infrared spectrum of compound “A”, C₃H₆O, shows a peak at 1730 cm^-1 and no peak at 2726 cm^-1. Suggest a structure for this compound.

5. A compound with a molecular formula C₂H₆O has an infrared spectrum which shows, amongst others, a broad absorption between 3200 - 3400 cm^-1 and a peak at 1380 cm^-1. Propose a structure for this compound.