41.2 - Loss of two hydrogen atoms from a compound designated by a trivial name is denoted by a prefix "didehydro-".
Example to Rule C-41.1
Note: In common usage "dehydro-" is often used in place of "didehydro-". For example the above compound is often termed dehydrocholesterol; another such example is dehydroascorbic acid, where "dehydro" denotes loss of hydrogen from two hydroxyl groups in the conversion of HO-C=C-OH into CO-CO at positions 2 and 3:
Example to Rule C-41.2
41.3 - As an exception, "deoxy-", when applied to hydroxy compounds, denotes replacement of a hydroxyl group by a hydrogen atom.
See Recommendations'93 R-1.2.5
Example to Rule C-41.3
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