Mass Spectroscopy, Example #1

Mass Spectroscopy, Example #2

Analysis: C₇H₁₂Br MW = 171.04 Help with Analysis

Mass Spectrum

Mass Spectrum

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C₇H₁₂Br MW = 171.04

From the molecular formula, the compound has "4 degrees of unsaturation" (four double bonds, rings or any combination thereof). The large number of degrees of unsaturation strongly suggests an aromatic molecule (DU = 4).

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The spectrum shows two small peaks of equal intensity in the molecular ion region, strongly suggesting that the molecule contains bromine (equal concentrations of the ⁷⁹Br and ⁸¹Br isotopes). The base peak represents loss of this bromine to give the peak at m/e = 91, which is highly suggestive of a benzyl fragment.

Fragmentation of Common Functional Groups
Common Ions and Fragments

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Structure:

IUPAC Name: bromomethyl benzene (benzyl bromide)

MS Fragments:

The spectrum shows two small peaks of equal intensity in the molecular ion region, strongly suggesting that the molecule contains bromine (equal concentrations of the ⁷⁹Br and ⁸¹Br isotopes ). The base peak represents loss of this bromine to give the peak at m/e = 91, which is highly suggestive of a benzyl fragment, which rearranges to form the tropylium cation.

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