Chapter 17, Problem 42P

Interpretation Introduction

Interpretation:

The product in each of the given reactions from their ${}^{\text{1}}\text{H}$ NMR spectra is to be identified. An explanation for the observed regioselectivity is to be suggested.

Concept Introduction:

In the ${}^{\text{1}}\text{H}$ NMR spectrum, the number of signals in a spectrum gives information about the type of proton present in the structure of the compound.

The chemical shift of a particular proton in the compound depends on the environment of the proton.

The signal of a particular proton is split by the presence of protons in vicinal position.

Index of hydrogen deficiency is calculated as

$\text{Index}\text{of}\text{hydrogen}\text{deficiency=}\frac{\text{1}}{\text{2}}\left({\text{C}}_{\text{n}}{\text{H}}_{\text{2n+2}}{\text{-C}}_{\text{n}}{\text{H}}_{\text{x}}\right)$, where $C_n{H}_x$ is the molecular formula of the compound

Presence of electronegative atoms in the structure de-shields the signals from their normal values.

The ideal range for protons in alkanes is $\text{δ}0.9\text{- δ}1.8$; for alcohol it is $\text{δ}0.5\text{- δ}5.0$; and, for aromatic protons it is $\text{δ}6.5\text{- δ}8.5$.

Epoxide rings are readily opened with cleavage of the carbon-oxygen bond when attacked by nucleophiles. Grignard reagents and organ lithium reagents react with epoxides by serving a source of nucleophilic carbon.

The nucleophilic carbon atom in the organometallic reagent attacks on the less substituted (less sterically hindered) carbon atom in the epoxide.

The mechanism resembles and ${\text{S}}_{\text{N}}\text{2}$ reactions.