What is the group that distinguishes aldehydes from most other classes of compounds?

The group that distinguishes alcohols from other classes of compounds is the hydroxyl group (OH).
Alcohols or alkanols are a group of hydrocarbon with a functional group; hydroxyl (OH) group that is attached to at least one carbon atom in a given compound. Alkanols consist of an alkane (compounds that contains carbon and hydrogen atoms single bonded to each other) that contains a hydroxyl group. 

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