ACCOUNTS OF CHEXICAL RESEARCH" Registered i n US.Patent and Trademark Office; Copyright 1982 by the American Chemical Society
VOLUME 15
NUMBER 2
FEBRUARY, 1982
EDITOR JOSEPH F. BUNNETT
Physical Organic Chemistry ASSOCIATE EDITORS Joel E. Keizer John E. McMurry
EDITORIAL ADVISORY BOARD Fred Basolo R. Stephen Berry Michel Boudart Maurice M. Bursey Edward A. Collins John T. Gerig Jenny P. Gleusher Kendall N. Houk Jay K. Kochi Maurice M. Kreevoy Theodore Kuwana Ronald N. McElhaney Eva L. Menger Kurt Mislow John C. Polanyi Alexander Rich Anthony M. Trozzolo Gene G. Wubbels
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Though important pioneering contributions were made as early as 1900, physical organic chemistry emerged as a field of inquiry only in the 1920s. Systematic thinking about mechanisms commenced, based on the recently recognized electronic theory of valency. And physical measurements-initially of dipole moments and by X-ray diffraction-initiated the physical determination of molecular structure. During the thirties, two major leaders emerged. In Britain, Christopher K. Ingold took a broad view of general reaction types such as substitutions, eliminations, and ester hydrolyses and used kinetic evidence to distinguish alternative mechanisms for reactions of seemingly similar type. For novel concepts, he invented novel terms, many of which are now standard in our language. In America, Louis P. Hammett developed rigorous thinking about the energetics of organic reactions, and he showed ways to make effective use of the extensive body of kinetic and thermodynamic data that had accumulated through the years. Those of us who entered physical organic chemistry just after World War I1 found gorgeous opportunities lying all about. Almost every textbook reaction cried for attention to its mechanism. We undertook to examine many of them, and on the whole our efforts were abundantly rewarded. The late fifties saw the emergence of a new generation of elementary organic chemistry textbooks in which reactions were presented throughout in terms of their mechanisms. Ideas of stereochemistry and mechanism became central to the thinking of synthetic organic chemists. Meanwhile, the physical determination of molecular structure, by means such as NMR, ESR, IR, and UV spectroscopy, mass spectrometry, and X-ray crystallography, became so successful that today the persons most expert in it are likely to be called natural products or analytical chemists. In the sixties, the field became somewhat troubled in spirit. As much had been learned about the mechanisms of common reactions, no longer were the nuggets of gold lying so obviously on the trail; one had to dig among the rocks at the side to find them, and it helped to have some idea of where to dig. Occasionally one saw a distinguished investigator make public pronouncements that the lode was nearly mined out; although these may have stemmed in part from personal ennui at finding the challenge and the excitement to be less than 20 years earlier, they were distressing to workers in the field and perhaps also to research-funding agencies. Certain lines of inquiry that had been pursued past the point of diminishing returns began to generate boredom. A major controversy concerning nonclassical carbonium ions caused much frustration as it persisted for years without any generally accepted resolution. An increasing emphasis on short-term objectives among research managers was a further difficulty. The rewards from research leading to deep understanding of a phenomenon are seldom tangible within the immediate fiscal year. Physical organic chemistry makes its greatest contribution through developing basic understanding as to how and why molecules behave as they do. This understanding, largely conveyed through textbooks, constitutes the backbone of modern organic chemistry and as such guides all its multitudinous practical applications. In recent years physical organic chemists have increasingly turned their attention to new areas of inquiry-among them organometallic reactions, electron transfer phenomena and host-guest interactions. These years have also seen increasing utilization, with much reward, of the tools of chemical physics. Thus the field has changed in a healthy way: it has seized opportunities to employ new techniques, it has relinquished territories conquered, and it has outgrown most of ita spiritual troubles of the sixties, although not the financial stringency that came with them. Joseph F. Bunnett
