Tuesday, 24 May 2005

This presentation is part of: Organic Posters

Assignment of 13C Chemical Shifts to Ring Carbons of Acetophenones

Donald D. Clarke, Fordham University, New York, NY

A substituent on a benzene ring alters delta at ring C atoms o- and p- to it depending on electronic sigma values, while the m- position is little affected. Nitrobenzene is an exception. There delta for the o- position is less than for m-; the opposite is predicted. The p- C behaves normally. In acetophenone the o- and m- C signals differ by 0.1-0.3 ppm. A JACS paper [94, 3089 (1972)] states that o- and m- assignments are unconfirmed, but suggested that o- signal has higher delta value. All databases copied this suggestion. We found by C-H COSY the opposite assignment is true. This seems to be a through space effect as invoked to explain the effect of the nitro group o- to itself. Phenacyl chloride and propiophenone behave similarly to acetophenone but &alpha,&alpha-dichloroacetophenone doesn't. Benzaldehyde, benzoic acid and methyl benzoate behave normally. Supported in part by NSF's Division of Undergraduate Education grant #9650684.

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