The natural abundance of 13c is 1.1%. what are the relative peak heights of the m+ and m+1 peaks in the mass spectrum of decane? how do you know?

a. 100: 11
b. 89: 11
c. 100: 1.1
d. 1: 1.1

a. 100:11

Explanation:

M+1 peak is observed due to the presence of an isotope of an atom in a molecule. Decane has the molecular formula C₁₀H₂₂, so the probability of having 13C atom in this molecule increases ten times. This gives the ratio between M+ and M+1 peak 100:11.

It should be noted that the decane molecule also contains hydrogen atoms whose isotope deuterium (2H) can also be present in the molecule and give M+1 peak. But its relative abundance to protium (1H) is low i.e., 0.015, so its effect can be neglected.

A simple formula for the estimation of the relative peak height of M+1 in a molecule that contains C, H, N, O, F, Si, P, and S is:

PS: remove the element from the formula which is not present in the molecule

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