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Chapter 14: Problem 1

Calculate the nominal mass of each ion. Unless otherwise indicated, use the mass of the most abundant isotope of each element. (a) \(\left[\mathrm{CH}_{3} \mathrm{Br}\right]^{+}\) (b) \(\left[\mathrm{CH}_{3}{ }^{81} \mathrm{Br}\right]^{+}\) (c) \(\left[{ }^{13} \mathrm{CH}_{3} \mathrm{Br}\right]^{+}\)

Short Answer

Expert verified
Answer: The nominal masses of the ions are (a) 94, (b) 96, and (c) 95.

Step by step solution

01

Identify the most abundant isotopes of each element

The most abundant isotopes for Carbon (C), Hydrogen (H), and Bromine (Br) are: - Carbon: \(^{12}C\) - Hydrogen: \(^{1}H\) - Bromine: \(^{79}Br\) (50.69%) and \(^{81}Br\) (49.31%)
02

Calculate the nominal mass of ion (a)

To calculate the mass of the ion \(\left[\mathrm{CH}_{3} \mathrm{Br}\right]^{+}\), use the most abundant isotopes for each element. Nominal Mass: Mass of Carbon + (3 x Mass of Hydrogen) + Mass of Bromine Nominal Mass = 12 + (3 x 1) + 79 = 94
03

Calculate the nominal mass of ion (b)

For ion (b), \(\left[\mathrm{CH}_{3}{ }^{81} \mathrm{Br}\right]^{+}\), we are indicated to use the isotope \(^{81}Br\). Nominal Mass = Mass of Carbon + (3 x Mass of Hydrogen) + Mass of \(^{81}Br\) Nominal Mass = 12 + (3 x 1) + 81 = 96
04

Calculate the nominal mass of ion (c)

For ion (c), \(\left[{ }^{13} \mathrm{CH}_{3} \mathrm{Br}\right]^{+}\), we are indicated to use the isotope \(^{13}C\). Nominal Mass = Mass of \(^{13}C\) + (3 x Mass of Hydrogen) + Mass of Bromine Nominal Mass = 13 + (3 x 1) + 79 = 95 So the nominal masses of the ions are: (a) 94 (b) 96 (c) 95

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Most popular questions from this chapter

Account for the presence of peaks at \(m / z 135\) and 107 in the mass spectrum of 4-methoxybenzoic acid ( \(p\)-anisic acid).

Determine the probability of the following in a natural sample of ethane. (a) One carbon in an ethane molecule is \({ }^{13} \mathrm{C}\). (b) Both carbons in an ethane molecule are \({ }^{13} \mathrm{C}\). (c) Two hydrogens in an ethane molecule are replaced by deuterium atoms.

What rule would you expect for the \(m / z\) values of fragment ions resulting from the cleavage of one bond in a compound with an odd number of nitrogen atoms?

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Write molecular formulas for the five possible molecular ions of \(\mathrm{m} / z 100\) containing only the elements \(\mathrm{C}, \mathrm{H}, \mathrm{N}\), and \(\mathrm{O}\).
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