Differences among the mechanisms of reaction of phenylhydroxylamine with various carbonyl compounds

In order to obtain a better knowledge of the special behavior of phenylhydr oxylamine asa nucleophile, the mechanism of its reaction with 2,6-dichlorob enzaldehyde, norcamphor, and cyclohexanone, and also the hydrophobic effect on its reaction with 2,6-dichlorobenzaldehyde and benzaldehyde, was studie d. The results led us to assume that the planar molecule of phenylhydroxyla mine should be placed parallel to the planar molecule of benzaldehyde in or der to permit the attack of the lone electron pair of the nitrogen on the c arbonyl group, forming, together with a hydrogen bond between the hydroxyl group and the carbonylic oxygen atom, a packed preassociation complex. This mechanism is not observed in the case of norcamphor or 2,6-dichlorobenzald ehyde due to the steric hindrances produced by the lack of planarity of the se molecules. (C) 2000 John Wiley & Sons, Inc.