Answer 7.4

The positive-ion isobutane-CI mass spectrum of a nitrophenyl-alkylether is shown below.

a) Write the composition to all peaks with a mass label, e.g. , identify the [M+H]+ etc.

b) Characterize the alkyl chain.

c) Can you identify which isomer belongs to the spectrum?

PICI spectrum of o-nitrophenyl-octylether

The difference of 112 u between [M+H]+ and the fragment ion at m/z 140 indicates octene loss, and thus an octyl chain. This is also reflected by the presence of an octyl ion, m/z 113. However, there is no hint in the spectrum that would clearly identify an n-octyl rather than iso-octyl or any other isomeric side chain.
In addition, the spectrum does not indicate the ortho-position of the substituent.

Note: 2-Nitrophenyl-octylether is used as a matrix in FAB-MS.