Q 10 P - Organic Chemistry (Mcmurry)

Question

Question: Where might the following compounds have IR absorptions?

Step-by-Step Solution

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 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.

Step 2: Chart for absorption by specific functional group

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

Step 3: 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.

Step 4: 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 ${\mathrm{cm}}^{-1}$ . 

Step 5: 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 ${\mathrm{cm}}^{-1}$ .