Q7P - Organic Chemistry (Mcmurry)

Question

What functional groups might the following molecules contain?

(a) A compound with a strong absorption at 1710 cm^-1 

(b) A compound with a strong absorption at 1540 cm^-1    

(c) A compound with strong absorptions at 1720 cm^-1   and 2500 to 3100 cm^-1    

Step-by-Step Solution

Answer

(a) Aldehyde or ketone

(b) Nitro group

(c) Carboxylic acid

Absorption spectrum

Absorption means presence of dark lines in spectrum of electromagnetic radiation which is transmitted through a substance indicating absorption at specific wavelengths.

Chart for absorption by specific functional group

The given chart for absorption of particular wavelength by specific functional group tells which functional group absorbs at which wavelength.

                                     Functional group absorption band

Part (a) absorption at 1710 cm -1

Here compound has strong absorption at 1710 cm^-1   which is only present in case of carbonyl compound. The carbonyl compound can be aldehyde or ketone. If it was an aromatic functional group then the weak intensity will be observed.

Part (b) absorption at 1540 cm -1

Hereit can be seen a compound hasa strong absorption at 1540 cm^-1  which is seen in the case of the nitro functional group so the functional group is nitro. 

Part (c) absorption at 1720 cm -1 and 2500 to 3100 cm -1

Herecompound is with strong absorptions at 1720 cm^-1 and 2500 to 3100 cm^-1 which is seen in the case of carboxylic acid as the carbonyl group of carboxylic acid has absorption at around 1710 cm^-1 and the hydroxyl group of carboxylic acid has absorption between 2500 to 3100 .