Question

Expt. 11/11x: Identification of an Unknown Carbonyl Compound by Infrared Spectroscopy

1. What is the unsaturation number for each of the following: C₅H₉BrO and C₇H₁₃NO.

Answer 1

ALDEHYDE	Aldehyde are having two weak absorptions to the right of the C-H stretch near 2850 cm-1 and 2750 cm-1 and are caused by the C-H bond that is part of the CHO aldehyde functional group. And carbonyl band around 1740-1720 cm-1.
KETONE	The weak aldehyde CH absorption bands will be absent.And carbonyl CO band around 1725-1705 cm-1.

Degree of Unsaturation:

A compound with formula C_aH_bN_cO_dX_e

where X is F, Cl, Br or I, and Ignore the Oxygen Molecules.

The degree of unsaturation is given by:

degree of unsaturation = 1/2 (2 + 2a - b + c - e).

C5H9BrO In this compound No. of C atoms (a) =5

No. of H atoms (b) =9

No. of Br atoms (e) =1 and substitute the values above formula,

degree of Unsaturation = 1/2 (2 + 2a - b + c - e)

=1/2(2+2*5-9-1)=1

degree of Unsaturation = 1

C7H13BNO  In this compound No. of C atoms (a) =7

No. of H atoms (b) =13

No. of N atoms (c) =1 and substitute the values above formula,

degree of Unsaturation = 1/2 (2 + 2a - b + c - e)

=1/2(2+2*7-13+1)=2

degree of Unsaturation = 2