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Multiple Choice
What would be the value of the base peak (m/z)?
A
48
B
57
C
68
D
75
Verified step by step guidance
1
Identify the molecular structure shown in the image. The image depicts a branched alkane, specifically isobutane, which has the chemical formula C4H10.
Understand that the base peak in mass spectrometry is the most intense peak, representing the most stable ion formed during fragmentation.
Consider the fragmentation pattern of isobutane. The most common fragmentation involves the loss of a methyl group (CH3), resulting in a tertiary carbocation.
Calculate the mass-to-charge ratio (m/z) of the resulting ion. The original molecular ion (C4H10) has a molecular weight of 58. The loss of a methyl group (CH3) reduces the mass by 15, resulting in an ion with a mass of 43.
Recognize that the base peak often corresponds to the most stable carbocation, which in this case is the tertiary butyl cation (C4H9+), with an m/z value of 57.