Organic Lab Reactions 110

Organic Lab Reactions 110 - DISUBSTITUTED BENZALDEHYDES 105...

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DISUBSTITUTED BENZALDEHYDES 105 Since it is highly probable that the Cannizzaro reaction proceeds by way of a step common to many addition reactions of the carbonyl group, namely, an initial attack upon the carbonyl carbon atom by a nucleo- philic reagent (for example, a strong base), the failure of o- and p- hydroxybenzaldehydes to undergo dismutation is readily explicable. In the presence of alkali the anionic oxygen formed by ionization of the phenolic hydroxyl group could, by virtue of its strongly basic nature, contribute to the resonance structure: 0 / - c <- \ H o- -> o=/ y=c \—/ \ H The effect may be considered a competition between one base (anionic oxygen) acting intramolecularly and another (hydroxyl ion) acting intermolecularly. The failure of, p-dimethylaminobenzaldehyde to react can be ascribed to a similar contribution of an electron pair from the basic dimethylamino grouping. If the hydrogen atom of the hy- droxyl group in o-
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This note was uploaded on 11/20/2011 for the course CHM 2210 taught by Professor Reynolds during the Fall '01 term at University of Florida.

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