Q26P - Organic Chemistry (Mcmurry)

Question

Propose structures for compounds that have the following formulas and IR absorptions:

(a) C₆H₁₂O₂, 1735 cm^-1 

(b) C₄H₉NO, 1650 cm^-1 

(c) C₄H₅ClO, 1780 cm^-1

 

Step-by-Step Solution

Answer

Structure of the three compounds can be given as:

Step 1: IR absorption at 1735 cm -1

Esters are detected by their absorption at 1735 cm^-1, a position somewhat higher than that for either aldehydes or ketones. So, the ester can have the following structure:

 

Step 2: IR absorption at 1650 cm -1

Amides absorb near the low-wavenumber end of the carbonyl region, with the degree of substitution on nitrogen affecting the exact position of the IR band. Disubstituted amides absorbs near 1650 cm^-1. So, the proposed structure for C₄H₉NO is 

Step 3: IR absorption at 1780 cm -1

Acid chlorides are easily detected by their characteristic absorption near 1810 cm^-1. Conjugated acid chlorides have absorption near 1770-1780 cm^-1.

Structure can be written as: