2,3-dimethylbutane gives a base fragment peak at m/z = 43.Which of the following is the most probable structure of the fragment ion?
A)I
B)II
C)III
D)IV

Question

2,3-dimethylbutane gives a base fragment peak at m/z = 43.Which of the following is the most probable structure of the fragment ion? 
A)I 
B)II 
C)III 
D)IV

Quizplus · Accepted Answer

The base peak at m/z = 43 is due to the loss of a methyl group from the tertiary carbon of the parent molecule (2,3-dimethylbutane). This can occur in structures III and IV, which both have a tertiary carbon with two methyl groups attached. However, structure IV has a secondary carbon adjacent to the tertiary carbon, which could result in a secondary fragmentation peak at m/z = 57. Therefore, the most probable structure of the fragment ion is III, which has only tertiary carbons in the vicinity of the methyl group loss.

2,3-Dimethylbutane Gives a Base Fragment Peak at M/z = 43