Question

4. (1 point) Predict the molecular formula for the compound whose mass spectrum is shown below 100 HS2016-05356CM Relative 10 100

Answer 1

The base peak of the spectrum is at m/z 57. so it may be straight-chain alkane or branched one.

for straight chain alkane, the molecular ion peak is present but weak.

incase, of branched-chain alkane, the molecular ion peak may be absent.

so either it is 2-methylpentane or 3-methylpentane.

fragmentation occurs at highly branched positions. As m/z is 57

CH3, H2 H, THI HỌC 3 2 н. с~CHз CH3 CÁCH, нс- нск Сн, 2-methylpentane 3-methylpentane Mol Wt = 86

fragmentation at the marked position will be below fragments

460 CH CH3 m/z = 43 m/z = 57

So, now it is clear that the peak at m/z = 57 is due to 3-methylpenatne.

ANSWER:

The molecular formula of the compound of the given spectrum is C₆H₁₄