6.11 Fragmentation of Ketones and Aldehydes

Both ketones and aldehydes give prominent molecular ion peaks though the [M+] peak is more prominent in ketones.  The majority of compounds in these categories undergo an important rearrangement, the McLafferty rearrangement.

This rearrangement is mediated by the p  systems of the carbonyl group but can occur in other p systems such as in nitriles (Section 6.17).  The only ketones and aldehydes that do not undergo this rearrangement are those which lack a side chain that can donate a hydrogen atom to the p system.  

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