Question

1. Show all your work calculating the # of Cs based on the Mand (M+1]' peaks. 2. Based on the mass spectrum, do you think your compound has a nitrogen atom? Explain. 3. Propose at least two molecular formulas based on the mass spectrum and calculate the exact mass of the parention. Is one of your formula more likely than the other? If so, explain.

Answer 1

1. No of carbons can be calculated from the relative intensity of [M+1] peak.

We have

Intensity of M⁺ peak (90) = 18.4

Intensity of [M+1] peak (91) = 0.83

We should make up the molecular ion peak to 100 % intensity to calculate the % abundance of [M+1]

Thus

if 18.4 intensity is 100 % then

0.83 intensity

(0.83/18.4) x 100 = 83/18.4 = 4.51 %

Thus the percentage abundance of [M+1] peak = 4.51 %

Now, we have the formula to calculate number of carbons

No. of carbons = % abundance of M+1 peak / ¹³C abundance %

We have % abundance of ¹³C = 1.1

Therefore the number of carbons = 4.51 / 1.1 = 4.1 $\approx$ 4

Thus the required number of carbons from M⁺ and M+1 peaks = 4.