Chapter 21, Problem 21.22P

Interpretation Introduction

Interpretation:

Expected mass of ${\text{C}}_{\text{4}}{\text{H}}_{\text{11}}{\text{N}}_{\text{3}}{\text{S}}^{+}$ and ${\text{C}}_{\text{4}}{\text{H}}_{\text{11}}{\text{N}}_{\text{3}}{\text{O}}^{+}$ has to be computed and ion that corresponds to measured $\text{m/z}$ value of 133.0686 has to be identified.

Concept Introduction:

Molecular mass is defined as mass corresponding to mass of one molecule of substance, while nominal mass may be defined as mass of most abundant isotope of a particular ion or molecule. For instance, carbon exist as two isotopes $\text{C-}12$ and $\text{C-}13$. $\text{C-}12$ is abundant as much as $98.9\text{ \%}$ while abundance of $\text{C-}13$ is only $\text{1}\text{.1 \%}$. So clearly nominal mass of carbon is $12\text{ g}$.

For instance, molecular mass of benzene is calculated by exact atomic masses of $\text{C}$ and $\text{H}$ atom as follows:

  $\begin{array}{c}{\text{Molecular mass of C}}_6{\text{H}}_{\text{6}}=\left(6\right)\left(12.0107\text{ u}\right)+\left(6\right)\left(1.0078\text{ u}\right)\\ =78.111\text{ u}\end{array}$

However, its nominal mass will take most abundant masses of $\text{C}$ and $\text{H}$ atoms into account and thus nominal mass is calculated as follows:

  $\begin{array}{c}{\text{Nominal mass of C}}_6{\text{H}}_{\text{6}}=\left(6\right)\left(12\text{ u}\right)+\left(6\right)\left(1\text{ u}\right)\\ =78\text{ u}\end{array}$