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Chapter 13: Q 1. (page 499)

Question: What is the mass of the molecular ion formed from compounds having each molecular formula:

(a) C3H6O; (b)C10H20;(c)C8H8O2; (d) methamphetamine (C10H15N)?

Short Answer

Expert verified

Answer

a. 58

b. 140

c. 136

d. 149

Step by step solution

01

Molecular ion

A molecular ion is formed by the bombardment of the given molecule with electron beams. It is a cation with a single unit positive charge and a radical with an unpaired electron.

02

Mass of molecular ions

Since the mass of the departing electron is almost negligible concerning the mass of the molecule, the mass of the molecular ion thus formed remains the same as the original molecule.

03

Determination of the mass

a. The mass of is the total mass of its substituents.

C3H6O = 3×12 + 6×1 + 1×16= 36 + 6 + 16= 58

Hence, the mass of the molecular ion of C3H6O is 58.


b. The mass of is the total mass of its substituents.

C10H20 = 10×12 + 20×1 = 120 + 20 = 140

Hence, the mass of the molecular ion of C10H20is 140.

c. The mass of is the total mass of its substituents.

C8H8O2 = 8×12 + 8×1 + 2×16= 96 + 8 + 32= 136

Hence, the mass of the molecular ion of C8H8O2 is 136.

d. The mass of is the total mass of its substituents.

C10H15N = 10×12 + 15×1 + 1×14= 120 + 15 + 14= 149

Hence, the mass of the molecular ion of C10H15N is 149.

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Most popular questions from this chapter

Question: The base peak in the mass spectrum of 2,2,4-trimethylpentane [(CH3)3CCH2CH(CH3)2] occurs at m/z = 57. What ion is responsible for this peak and why is this ion the most abundant fragment?

Question:Benzonitrile (C6H5CN) is reduced to two different products depending on the reducing agent used. Treatment with lithium aluminum hydride followed by water forms K, which has a molecular ion in its mass spectrum at 107 and the following IR absorptions: 3373, 3290, 3062, 2920, and 1600 cm-1. Treatment with a milder reducing agent forms L, which has a molecular ion in its mass spectrum at 106 and the following IR absorptions: 3086, 2820, 2736, 1703, and 1600 cm-1. L shows fragments in its mass spectrum at m/z= 105 and 77. Propose structures for K and L and explain how you arrived at your conclusions.

Question: Treatment of anisole (CH3OC6H5)with Cl2 and FeCl3forms P, which has peaks in its mass spectrum at m/z = 142 (M), 144 (M + 2), 129, and 127. P has absorptions in its IR spectrum at 3096–2837 (several peaks), 1582, and 1494 cm–1. Propose possible structures for P.

Question: What molecular ions would you expect for the compound depicted in the ball-and-stick model?

Question: What functional groups are responsible for the absorptions above 1500 cm-1in the IR spectra for compounds A and B?
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