Q10P - Organic Chemistry (Mcmurry)

Question

Where might the following compounds have IR absorptions?

Step-by-Step Solution

Answer

a. Absorption bands at 1715 cm^-1 and 1640-1680 cm^-1 

b. Absorption bands at 1730 cm^-1  , 2100 - 2260 cm^-1  and 3300 cm^-1 . 

c. Absorption bands at 1710-1760 cm^-1  , 2500-3100 cm^-1 , 3400-3650 cm^-1 , 3030 cm^-1 and 1450 - 1600 cm^-1  . 

Absorption spectrum

The absorption spectrum shows the presence of dark lines in the spectrum when transmitted through a substance indicating absorption at specific wavelengths of electromagnetic radiation.

Chart for absorption by specific functional group

The given chart shows absorption of particular wavelength radiation by specific functional group.

Part (a) absorption spectrum

Here two absorption bands will be seen. One for ester group at 1715 cm^-1  and one for alkene group - C = C - at to 1640-1680 cm^-1  . The value for ester group absorption is less due to presence next to double bond.

Part (b) absorption spectrum

Here three absorption bands will be seen. One for aldehyde carbonyl group at 1730 cm^-1 , one for alkyne - C _$\equiv$C -  at 2100 - 2260 cm^-1 and one for _$\equiv$C-H alkyne at 3300 cm^-1 . 

Part (c) absorption spectrum

Here five absorption bands will be seen. One for carbonyl group of carboxylic acid at 1710-1760 cm^-1, one for hydroxyl group in carboxylic acid at 2500-3100 cm^-1 , one for hydroxyl group at 3400-3650 cm^-1, two for aromatic ring at 3030 cm^-1 and 1450 - 1600 cm^-1.