Supra-annular effect

Electronic effects can also influence the ease of double bond hydrogenation. Compounds such as A cyclohexenecarboxaldehyde (4) and other 3-carbonyl substituted cyclohexenes, such as 5 and 6, are more difficult to hydrogenate than the non-carbonyl containing materials. This decrease in activity has been attributed to an interaction between the carbonyl carbon and the 7t cloud of the double bond, shown by 7, which has been termed a supra-annular effect.7-"... 

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