The McLafferty rearrangement is a fragmentation method used in mass spectrometry to differentiate between isomers. In this process, a molecule undergoes a dissociation reaction, leading to the formation of a smaller, stable molecule.


The McLafferty rearrangement of 2-methylbutanal and 3-methylbutanal involves the cleavage of the carbon-oxygen bond adjacent to the carbonyl group. The resulting fragment ions are different for each isomer, allowing for their differentiation.


When 2-methylbutanal undergoes McLafferty rearrangement, the carbon-oxygen bond adjacent to the carbonyl group is cleaved, leading to the formation of a fragment ion with a mass of 57. This ion corresponds to the loss of a methyl group from the original molecule. Additionally, a fragment ion with a mass of 43 is formed, which corresponds to the loss of a methyl group and the carbonyl group.


When 3-methylbutanal undergoes McLafferty rearrangement, the carbon-oxygen bond adjacent to the carbonyl group is cleaved, leading to the formation of a fragment ion with a mass of 71. This ion corresponds to the loss of a methyl group and a hydrogen atom from the original molecule. Additionally, a fragment ion with a mass of 57 is formed, which corresponds to the loss of a methyl group.


The McLafferty rearrangement can be used to differentiate between 2-methylbutanal and 3-methylbutanal based on the fragment ions formed during the dissociation reaction. 2-methylbutanal forms a fragment ion with a mass of 57, while 3-methylbutanal forms a fragment ion with a mass of 71. This method is useful for identifying isomers in complex mixtures and can provide valuable information for chemical analysis.