Chapter 14, Problem 14.37P

Interpretation Introduction

Interpretation:

Given tetrahydrocannabinol exbits two strong ftragement ions at $m/z246,and231$ and stracture of each ions have to be determined.

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.

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

Interpreting a mass spectrum:

1. 1. The each $m/z$ values is the $m/z$ value of one the fragments to the nearest whole number.
2. 2. The peak with the highest $m/z$ value in the molecular ions $\left({\text{M}}^{\text{+}}\right)$, the fragment that results when the molecules lose electrons as result of being bombarding by the electron beam.
3. 3. The $m/z$ value of the molecular ion gives the molecular mass of the compound.

Peaks with smaller m/z values, fragment ion peak represent positively charged fragments of the molecular ion.

Diels-Alder reaction:

A conjugated diene reacts with a compound containing a carbon-carbon double bond.  It is a cycloaddition reaction, where two reactants form a cyclic product.

Rule: The stabilities of carbocation are,

$\begin{array}{l}{\text{Benzyl cation = allyl cation = 3}}^{\text{o}}{\text{carbocation > 2}}^{\text{o}}{\text{ carbocation > 1}}^{\text{o}}\text{ carbocation > }\\ \text{methyl cation > vinyl cation}\end{array}$