Question

Use the data below from an electron impact mass spectrum of a pure compound to deduce its structure.

Mass Spectrum
M/z Relative intensity
66 32
64 100
49 26
29 72
28 83
27 60

Answer 1

The 3:1 doublet at m/z=64 and 66 is the characteristic "isotope cluster" for one chlorine atom. The compound contains chlorine.

The molecular ion (and molecular weight) is 64. (M/z=66 is the 37Cl isotope peak at M+2.)

Subtracting the mass of 35Cl from the mass of the molecular ion, 64, leaves 29 daltons unaccounted for. This is exactly the mass of ethyl. Thus, this is probably chloroethane.

The peak at m/z=29 is ethyl cation.
That at m/z=28 is ethene radical cation(CH2=CH2 .+) from loss of HCl from the molecular ion.

These and the peak at m/z=49 from loss of methyl from the molecular ion support this conclusion.

Answer 2

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