Question

The following are the m/z values and attending peak intensities(in brackets) for the molecular ion and the M+1 peak of a compound. Propose a molecular formula.

M+. = 136 (61.7%)

M+1 =137 (6.6%)

Please explain step by step!

Answer 1

According to the given data:

The mass of molecular ion peak is an even number, i.e. there is no nitrogen in the molecular formula.

Rule of 13 (mass of one CH) gives 136/13 = 10 (with the remainder 6)

i.e. One of the possibilities is the molecular contains 10*CH and 6*H = C₁₀H₁₆

The second possibility is including one oxygen atom (mass = 16) instead of one CH₄ unit (12 + 4), i.e. C₉H₁₂O

The third possibility is including two oxygen atoms (mass = 2*16) instead of two CH₄ units (mass = 2*16), i.e. C₈H₈O₂

Most probable structure is C₉H₁₂O