Chapter 16, Problem 16.7P

Interpretation Introduction

Interpretation:

How many chemically distinct H atoms are there in chloroethene, ${\text{H}}_{\text{2}}\text{C=CHCl}$, is to be determined.

Concept introduction:

Sometimes, it is not immediately obvious whether certain hydrogen atoms in a molecule are chemically distinct. In such cases, the chemical distinction test is used.

Chemical distinction test: The complete structure of the molecule is to be drawn in which just hydrogen atom is replaced by an imaginary “X” atom. There should be one X-substituted molecule for each hydrogen atom being tested.

If the chemical distinction test yields enantiomers, then the corresponding hydrogen atoms are said to be enantiotopic. If the test yields diastereomers, then the corresponding hydrogen atoms are said to be diastereotopic.

Enantiotopic and diastereotopic hydrogens are distinct in $\text{H}$ NMR spectrum.