Question

Question: Where might the following compounds have IR absorptions?

Short answer

a. Absorption bands at 1715${\mathrm{cm}}^{-1}$ and 1640-1680 ${\mathrm{cm}}^{-1}$

b. Absorption bands at 1730${\mathrm{cm}}^{-1}$ , 2100 - 2260 ${\mathrm{cm}}^{-1}$and 3300${\mathrm{cm}}^{-1}$ .

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

Step-by-step solution

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${\mathrm{cm}}^{-1}$ and one for alkene group$-\mathrm{C}=\mathrm{C}-$ at to 1640-1680${\mathrm{cm}}^{-1}$ . 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${\mathrm{cm}}^{-1}$ , one for alkyne$-\mathrm{C}\equiv \mathrm{C}-$ at 2100 - 2260 ${\mathrm{cm}}^{-1}$and one for alkyne$\equiv \mathrm{C}-\mathrm{H}$ at 3300${\mathrm{cm}}^{-1}$ .

Part (c) absorption spectrum

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