In this mass spectrum, which peak most likely represents the molecular ion? 𝑚𝑧=85 𝑚𝑧=100 𝑚𝑧=71 𝑚𝑧=29 𝑚𝑧=57 𝑚𝑧=43

Question

https://content.macmillan-learning.com/cms-nga/7079ba6b57e0d5f262999372628894ee13101e5d/480503_spectrum.PNG

Picture of graph

Answer 1

When working with small molecules, the largest ion is usually the molecular or "parent" ion. When compounds are ionized in a mass spec, they can fragment into smaller ions, so the largest ion is likely the non fragmented form. Because mass specs measure mass/charge (m/z) some compounds can be multiply charged and the parent ion may not be the largest ion observed, but this is unlikely in a small molecule such as the spectra listed in this question.

Also, one can tell this compound has some alkane components due to the recurring mass shifts of 14 m/z (CH2).