Chapter 3.1, Problem 3.9P

Interpretation Introduction

Interpretation:

The number of signals expected in the proton NMR spectrum of the given compound has to be determined.

Concept Introduction:

The number of signals in a proton NMR spectrum indicates the number of different types of protons.  Chemically equivalent protons which are in identical chemical environment will produce only one signal.

Rules for identification of number of different protons:

• The two protons of a $C{H}_2$ group will be chemically equivalent if the compound lacks stereo centers.  But if the compound has a stereo center, then the protons of a $C{H}_2$ group will not be chemically equivalent.
• Two $C{H}_2$ groups will be equivalent to each other if the $C{H}_2$ groups can be interchanged by either rotation or reflection.
• The above rule also applies for $C{H}_3$ groups or $CH$ groups.
• The three protons of a $C{H}_3$ group are always chemically equivalent, even if there are stereo centers in the compound.