Chapter 21, Problem 21.20P

(a)

Interpretation Introduction

Interpretation:

With the help of given mass values, infrared and ${}^{\text{1}}\text{H NMR}$ spectrums, structural formula of compound Chas to be deduced.

Concept Introduction:

Mass spectrum: It generates multiple ions from the sample under investigation, it than separates them according to their specific mass to charge ration $\left(m/z\right)$ and records the relative abundance (RA) of each ion types.

    $\begin{array}{l}\text{M}\stackrel{\begin{array}{l}\text{electron}\\ \text{beam}\end{array}}{\to }{\text{M}}^{\begin{array}{l}+\\ .\end{array}}+{\text{e}}^{\text{-}}\\ \text{[Molecule]}\text{Molecular ion}\text{electron}\\ [\text{Radical}\text{cation}]\end{array}$

The ${}^{1}HNMR$ spectrum of a compound provides some vital information that is required to predict the structure of the compound.  The chemical shift values can predict the groups that are present in the molecule.  The splitting of signals by the $\left(\text{N+1}\right)$ rule predicts the number of hydrogens or protons attached to the adjacent carbon in a carbon chain of a compound.  Withthis information, the structure of the compound can be predicted.

IR Spectrum: It is concerned with the study of absorption of infrared, which causes vibration transition in the molecule. It is mainly used to identify functional groups present in molecules.

(b)

Interpretation Introduction

Interpretation:

The apperance of peaks in the mass spectrum of compound C at the given $\text{m/z}$ values has to be accounted.

Concept introduction:

Basic principle of mass spectrum: It generates multiple ions from the sample under investigation, it than separates them according to their specific mass to charge ration $\left(m/z\right)$ and records the relative abundance (RA) of each ion types.

    $\begin{array}{l}\text{M}\stackrel{\begin{array}{l}\text{electron}\\ \text{beam}\end{array}}{\to }{\text{M}}^{\begin{array}{l}+\\ .\end{array}}+{\text{e}}^{\text{-}}\\ \text{[Molecule]}\text{Molecular ion}\text{electron}\\ [\text{Radical}\text{cation}]\end{array}$

Alpha$\alpha$ cleavage: This cleavage in mass spectrometry is a characteristic fragmentation of the molecular ion derived from carbonyl compound, in which the bond linking the carbonyl carbon to the atom occupying an alpha position breaks.

It is an expected pathway for carbonyl compounds, ethers, halide, alcohols and amines.