Chapter 44: Problem 3

Search the MassBank (http://www.massbank .jp/) database for the spectrum for bromobenzene. (a) What does the \(77 \mathrm{~m} / \mathrm{z}\) ion represent? (b) What features are characteristic of bromine? (c) How many stable isotopes does bromine have? (d) How would you confirm that it is bromobenzene?

Short Answer

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The \(77 m/z\) ion signifies the benzene ion. Bromine’s unique feature lies in its isotopic pattern where two prominent peaks are seen at \(m/z 79\) and \(m/z 81\). Bromine has two stable isotopes: \(^{79}Br\) and \(^{81}Br\). Bromobenzene can be confirmed by its molecular ion peak at \(m/z 157\) and the presence of other specific peaks.

Step by step solution

Understand What a '77 m/z' Ion Represents

The Mass-to-charge (m/z) ratio of 77 can be linked to the aromatic ring compound of bromobenzene. It signifies a benzene ion.

Identify Features Characteristic of Bromine

Bromine in a mass spectrum often presents a characteristic isotopic pattern due to its two stable isotopes \(^{79}Br\) and \(^{81}Br\). This leads to two major peaks at \(m/z 79\) and \(m/z 81\). The isotopic pattern is close to 1:1 ratio because the natural abundance of these two isotopes is nearly equal.

Determine the Number of Stable Isotopes Bromine Has

Bromine has two stable isotopes, which are \(^{79}Br\) and \(^{81}Br\).

Confirming it is Bromobenzene

Bromobenzene can be identified in the mass spectrometry based on its molecular ion peak at \(m/z 157\). Also, confirm it by matching the spectral pattern and other specific peaks such as those at \(m/z 77\) (benzene ion), \(m/z 79\) and \(m/z 81\) (isotopic peaks for bromine).

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Short Answer

Step by step solution

Understand What a '77 m/z' Ion Represents

Identify Features Characteristic of Bromine

Determine the Number of Stable Isotopes Bromine Has

Confirming it is Bromobenzene

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