Steric effects on mesomerism: I. General considerations on the deacylation of aromatic acylaminocompounds with a nitro group in the ortho‐ or para‐position

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Abstract
This paper is the first of a series dealing with an investigation of the rates of deacylation of aromatic acylamino compounds having a nitro group in ortho‐ or para‐position, with the aim of obtaining further (semi‐) quantitative information with regard to “steric effects on mesomerism” (“steric hindrance of resonance”).In the first section some remarks on the nomenclature have been made, more in particular on the use of the “neutral” word “effect”, rather than the more customary “hindrance”. Further, it has been pointed out that the so‐called “Mills‐Nixon effect” should be regarded as a special case of steric effects on mesomerism, viz. as a steric effect on mesomerism due to changes in valency angles.The mechanism of the deacylation has been discussed in some detail; the mesomerism in the ortho‐ or para‐nitrophenylamino grouping is regarded to be mainly responsible for the “catalytic” deacylation.The question as to whether the slow deacylation observed in some cases might be caused by steric hindrance in the classical sense, rather than by steric effects on mesomerism, has been considered, the conclusion being that steric hindrance is certainly not of prime importance.In the last section the method by which the rates of deacylation are compared in order to get an insight into the magnitudes of the steric effects on the mesomerism, has been given and discussed briefly.

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