Chapter 15, Problem 15.15YT

Interpretation Introduction

Interpretation:

All of the peaks in Figure 15-20 that correspond to $\text{N-H}$ stretching modes of vibration are to be identified.

Concept introduction:

$\text{N-H}$ stretches appear between $\text{33}00$ and ${\text{3500 cm}}^{\text{-1}}$. Hydrogen bonding involving $\text{N-H}$ bonds usually causes these bands to be moderately broad. The intensity of an $\text{N-H}$ stretch is usually less than that of an $\text{O-H}$ stretch. An $\text{N-H}$ absorption band is usually not as broad as an $\text{O-H}$ one. The number of $\text{N-H}$ peaks that appear can be used to distinguish between various types of amines or amides. A primary amine (${\text{RNH}}_{\text{2}}$) or amide (${\text{RCONH}}_{\text{2}}$) exhibits two separate (but closely spaced) $\text{N-H}$ stretching bands. A secondary amine (${\text{R}}_{\text{2}}\text{NH}$) or amide ($\text{RCONHR}$) exhibits one $\text{N-H}$ stretching band. A tertiary amine (${\text{R}}_{\text{3}}\text{N}$) or amide (${\text{RCONR}}_{\text{2}}$) exhibits no $\text{N-H}$ stretching bands.