ORGANIC CHEMISTRY BOOK& SG/SM
ORGANIC CHEMISTRY BOOK& SG/SM
6th Edition
ISBN: 9781264094493
Author: SMITH
Publisher: MCG
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Chapter 12A, Problem 15P

The mass spectrum of the following compound shows fragments at m / z = 127, 113, and 85. Propose structures for the ions that give rise to these peaks.

Chapter 12A, Problem 15P, Problem-13.24 The mass spectrum of the following compound shows fragments at  = 127, 113, and 85.

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Interpretation Introduction

Interpretation: The structures of the ions of a given compound that shows fragments at m/z=127,113 and 85 is to be proposed.

Concept introduction: Molecular ion is the radical cation which is formed by ejection of electrons from a molecule when a beam of high-energy electrons bombarded on a molecule. Mass of the molecule is equal to m/z value of the molecular ion.

Answer to Problem 15P

The fragments of 3-ethyl, 3-methylheptane at m/z=127, m/z=113 and m/z=85 are shown below.

ORGANIC CHEMISTRY BOOK& SG/SM, Chapter 12A, Problem 15P , additional homework tip  1

Explanation of Solution

The ball and stick model of the given compound is,

ORGANIC CHEMISTRY BOOK& SG/SM, Chapter 12A, Problem 15P , additional homework tip  2

Figure 1

Black colored atoms have four bonds. So, these are the carbon atoms. The grey colored balls have one bond. So, these are the hydrogen atoms. The molecular structure is,

ORGANIC CHEMISTRY BOOK& SG/SM, Chapter 12A, Problem 15P , additional homework tip  3

Figure 2

Hence, the ball and stick model of the given compound is 3-ethyl, 3-methylheptane. The mass of 3-ethyl, 3-methylheptane is follow.

Mass of C10H22=(10×Mass of C atom + 22×Mass of H atom)=(10×12+22×1)=(120+22)=142 g/mol

Thus, the molecular ion peak of 3-ethyl, 3-methylheptane is observed at m/z=142.

The molecular ion (m/z=142) loses methyl radical (M15) to give a fragment ion at m/z=127.

The molecular ion (m/z=142) loses ethyl radical (M29) to give a fragment ion at m/z=113.

The molecular ion (m/z=142) loses butyl radical (M57) to give a fragment ion at m/z=85.

Hence, the fragments of 3-ethyl, 3-methylheptane at m/z=127, m/z=113 and m/z=85 are shown below.

ORGANIC CHEMISTRY BOOK& SG/SM, Chapter 12A, Problem 15P , additional homework tip  4

Figure 3

Conclusion

The fragments of 3-ethyl, 3-methylheptane at m/z=127, m/z=113 and m/z=85 are shown in Figure 3.

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