Distinguished Professor Emeritus of Chemistry and Biochemistry (Recalled)

Office: Pacific Hall 5223A
Phone: 858-534-2164
Email: cperrin@ucsd.edu
Web: https://chemistry.ucsd.edu/faculty/profiles/perrin_charles_l.html

Group: View group members
Accepting Rotation Students: No

2022

Distinguished Professor in the Graduate Division

2017

Distinguished Scientist Award of ACS San Diego Section

2015

American Chemical Society James Flack Norris Award in Physical Organic Chemistry

2014-2016

Murray Goodman Endowed Chair

2013

Andrew Streitwieser Lecturer, UCBerkeley

2012

Wawzonek Memorial Lecturer, University of Iowa

2011

Visiting Professor, Gothenburg Univrsity

2008

Phi Beta Kappa lecturer, UCSD

2001

UCSD Chancellor's Associates' Faculty Excellence Award for teaching

1994

UCSD Academic Senate Distinguished Teaching Award

1993

Danish Research Academy Visiting Professor

1986

NATO Visiting Professor, University of Padua

1984

Fellow, Amer. Assn. Adv. Science

1972-1973

NIH Special Research Fellow, Gothenburg University

1967

Alfred P. Sloan Fellow

1963

NSF Postdoctoral Fellow, University of California, Berkeley

Our research in physical-organic chemistry is concerned with molecular structure, mechanisms of organic reactions, and effects of structure on reactivity. Areas of current activity include NMR studies of hydrogen-bond symmetry, of isotope effects, of stereochemical effects on reactivity, of the anomeric effect, and of steric hindrance.

Is a hydrogen bond symmetric or asymmetric? The NMR method of isotopic perturbation can answer this for monoanions of 18O-labeled dicarboxylic acids and for various NHN species. The former had always been considered as having a symmetric intramolecular hydrogen bond. Nevertheless, the observed 13C spectra show that all of these exist as a pair of tautomers in solution.

Cationic groups were thought to prefer the equatorial position on a sugar molecule. We reinvestigated this so-called reverse anomeric effect by measuring axial/equatorial ratios of various glucosylamines and glycosylimidazoles. The conformational changes that occur upon N-protonation can be accounted for on the basis of steric effects and an enhancement of the normal anomeric effect. Substituted glucosylanilines fine-tune the localization of positive charge, which increases the steric hindrance to ionic solvation but enhances the anomeric effect to an even greater extent.

A highly accurate (±0.002 pH units!) NMR titration method, applicable to a mixture of closely related molecules, has been developed. We use this method to measure isotope effects on basicity and steric hindrance to ionic solvation. For amines we have demonstrated that the increased basicity on deuteration is of stereoelectronic origin. In contrast, computations and experimental evidence show that the well-known reduction of one-bond NMR coupling constants is not due to lone-pair delocalization, even though this had been the accepted interpretation for forty years.

We have discovered a remarkable new reaction, the addition of nucleophiles to a p-benzyne biradical. As evidence, we showed that the enediyne cyclodeca-1,5-diyn-3-ene, in the presence of lithium halide and a weak acid, can be converted to a good yield of 1-halotetrahydronaphthalene. The reaction is simply first-order in enediyne, and independent of the concentrations of acid and halide. These kinetics are consistent with rate-limiting cyclization to a p-benzyne biradical that rapidly adds halide, to form an aryl anion, which is then protonated. The reaction thus involves nucleophilic addition of halide, which is novel and quite different from the usual radical reactivity of a p-benzyne biradical.

The aldol condensation is a key reaction of organic chemistry, but its complete mechanism had never been elucidated. Now, through solvent kinetic isotope effects we have shown that Step 5, the final loss of hydroxide, is rate-limiting in the reactions between a benzaldehyde and an acetophenone.

Bioorganic
Physical Organic
Physical Organic

symmetric or asymmetric hydrogen bond?

transition state for decomposition of malonic anhydride to ketene + CO2

nucleophilic addition to para-benzyne diradical