Abstract
Using the intrinsic bond orbital (IBO) analysis based on accurate quantum mechanical calculations of the reaction path for the epoxidation of propene using peroxyacetic acid, we find that the four commonly used curly arrows for representing this reaction mechanism are insufficient and that seven curly arrows are required as a result of changes to σ and π bonding interactions, which are usually neglected in all textbook curly arrow representations. The IBO method provides a convenient quantitative method for deriving curly arrows in a rational manner rather than the normal ad hoc representations used ubiquitously in teaching organic chemistry.
Highlights
Arrow depictions[1,2,3] of how bonds break and form during chemical transformations have been ubiquitous in both textbooks and research articles for seventy years or more
We have previously demonstrated for the Claisen rearrangement[12] that transformations between σ and π bonds can be identified when following reaction paths using intrinsic bond orbital (IBO)
We identified a single transition state which led to the formation of the desired epoxide product with a corresponding intrinsic reaction coordinate (IRC) followed from the transition state for this reaction that reveals both a complex formed at the end of the reaction with an intermolecular OH hydrogen bond and a
Summary
Arrow depictions[1,2,3] of how bonds break and form during chemical transformations have been ubiquitous in both textbooks and research articles for seventy years or more. These changes include (i) the nucleophilic attack of the C C π-bond onto the assumed electrophilic oxygen of the peracid unit, (ii) transformation of the O H bond of the peracid unit into a new C O bond of the epoxide product, (iii) breaking of the O O bond in which the electron pair is transformed into the C=O bond of the carboxylic acid by product and (iv) transformation of the πbond of the C=O bond in the starting peracid into an O H bond For this particular mechanism at times the end-point of the curly arrow indicating the formation of a given bond can differ such that the termination of (some) arrow heads ends directly at an atom (Scheme 1(b)).[4,8]. Arrows for the epoxidation of propene by peracetic acid as derived from the IBO analysis
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