Half a century of research, teaching, service

Abstract

This is a summary of the research of Charles L. Perrin and his coworkers in the areas of aromatic mercuration, vibronic borrowing, ipso factors in electrophilic aromatic substitution, malonic anhydrides, mechanisms of proton exchange in amides, stereoelectronic control, the socalled reverse anomeric effect, an NMR titration method for highly accurate measurement of relative acidities, secondary deuterium isotope effects on acidity, symmetry of hydrogen bonds in solution, and nucleophilic addition to a para-benzyne diradical, along with Perrin's contributions to teaching and to service. Keywords:hydrogen bonds para-benzyne NMR titration isotope effects stereoelectronic control reverse anomeric effect vibronic borrowing electrophilic aromatic substitution malonic anhydrides proton exchange in amides Special thanks go to my dear wife Marilyn for her presence and support during these fifty years and for preparing a delicious dinner for the speakers and out-of-town guests the night before the symposium.After 50 years at UCSD I am still not retired but continue to enjoy teaching and research.

Symmetry of [N–X–N]+halogen bonds in solution

“…The small difference (B0.2 A ˚) between the N-X bond lengths of the symmetric and hypothetic asymmetric structures of 1 and 2 as compared to that of 3 (0.6 A ˚) provides a plausible explanation for this observation. An important and previously not reported 27 observation is that the intrinsic IE is slightly altered upon secondary chemical interactions, here to halogens or protons, which is here qualitatively reproducible by the applied theory.…”

The Logic behind a Physical–Organic Chemist’s Research Topics

“…All that is required to make them equivalent is rotation about the C-N bond, which has become single. In RCOCH 3 , which is isoelectronic to RCONH 3 + , that rotation has a barrier of ~1 kcal/mol, so that the rate of rotation is ~10 12 s -1 . But RCONH 3 + is an exceedingly strong acid, with a pK a estimated as -8.…”

“…The proton on the nitrogen is thereby acidified, so that it can be removed, to form the imidic acid, RC(OH)=NH, as an intermediate (Scheme 2c). Reversal of those two steps then achieves proton exchange without requiring formation of the strongly acidic and therefore high-energy RCONH 3 It occurred to me that it ought to be possible to distinguish between the two mechanisms with primary amides, RCONH 2 . Because of the C-N partial double-bond character, the two NH are in different environments.…”

“…The reason that I won the James Flack Norris Award was for my “insight, rigorous analysis, and understanding of mechanisms and reactive intermediates”, rather than any distinctive area of research with which I am associated. Instead of choosing one area to review here, I have tried to describe the path of my research for the past 40 years, as an expansion of an earlier article on this topic . Each area seems to have engendered additional questions, leading to additional areas.…”

“…Instead of choosing one area to review here, I have tried to describe the path of my research for the past 40 years, as an expansion of an earlier article on this topic. 3 Each area seems to have engendered additional questions, leading to additional areas. Often those questions are marked by an intense skepticism, and the answers to those questions are supported by a logical analysis that I am proud of.…”