Click on any numbered peak for help in interpreting this spectrum.
The peak occurs at m/e = 65. This is a characteristic fragmentation which is often seen when a peak at m/e = 91 is present.
The peak occurs at m/e = 91, making this peak m-80 (loss of a bromine) and the base peak in this spectrum. A fragment of m/e = 91 is characteristic of a benzyl unit, fragmenting to form a tropylium ion.
These peaks occurs at m/e = 170 and 172, making these the molecular ions (m.+). Twin molecular ions such as these are observed when bromine is present in the molecule because bromine consists of two isomers, MW 79 and 81, at approximately equal concentrations.
C7H7Br 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).
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.
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.
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Structure: 
