Rethinking Organic Chemistry: Enhancing Pedagogies to Explain the Relative Reactivity of Aldehydes and Ketones

In this work, we explore the structure and charge distribution within carbonyl compounds. It is routine in textbook explanations to attribute the relative reactivity of aldehydes and ketones to electron-donating effects of alkyl groups. The results of our computational study indicate that the changes in charge distribution contradict the common textbook explanations. Neither the inductive effect nor the hyperconjugation effect of a methyl group lower the partial positive charge on a carbonyl carbon atom, and the incorporation of halogens adjacent to the carbonyl does not increase the partial positive charge. We must attribute the stabilization exclusively to differing hyperconjugation effects, and we use NBO analysis of hyperconjugation interactions to quantify the relative stabilization of carbonyl compounds by representative groups. As a result, there is an opportunity to develop a more coherent framework for teaching carbonyl chemistry, which intersects with alkene reactivity and carbocation stabilization.