Physical Organic Chemistry for the 21st Century
Summary
The essays that follow are from 20 different individuals,
all of them distinguished for their research, and also for their willingness
to think broadly about science and its future. Many of them are not known
as physical organic chemists, but all of them have used the tools of this
discipline in their work, and comment upon the utility of this discipline
for the practice of other areas of chemistry as well.
The authors were given great latitude in composing
their contributions, and the diversity of approaches that resulted is just
what was sought, as it shows the wide range of the field. It is indicative
of the evolution of the field that the venerable names of the affiliations
of two of the contributors changed during the year this collection was assembled,
as the Department of Chemistry at Harvard University became the Department
of Chemistry and Chemical Biology, and CIBA-Geigy and Sandoz became the Novartis
Corporation. Thus both in academia and in industry institutions change to
better reflect the nature of the field, and to anticipate the future.
The theme runs through all of the essays that the
future of the field lies in an interdisciplinary approach and that physical
organic chemists will use all of the tools available, and will not be fettered
to narrow views. Physical organic chemistry will be active in the 21st Century
in the elucidation of the interrelation of chemistry and biology, in the design
and construction of new materials and molecular devices, in the study of chemical
processes in solution, gas, and solid phase, and at extremes of conditions.
Computational chemistry will play an increasing role, and new instrumental
techniques will be widely utilized. The field of materials will receive increasing
attention, particularly in the application of the understanding of the origins
of chemical properties and detailed mechanisms of reactions to the design
of materials and devices for specific purposes.
Physical organic chemistry will also be increasingly
involved in education, in profit-making activities, and in political activity.
Courses in physical organic chemistry are taught all over the world to advanced
undergraduates and graduate students, and are seen by many outside the discipline
as an essential part of the training for individuals who throughout their
careers will have to respond in creative ways to an ever-changing science.
Teachers will be called upon to provide fundamental understanding and a flexible
approach to problem solving so that future challenges can be met. New textbooks
that present in a managable fashion the increasingly diversified subject matter
of the field will also be needed.
Some are skeptical about the future of physical organic
chemistry, and about the use of an exercise such as this. The pessimists who
believe the field has no place to progress harken back to some who felt the
area was exhausted over 30 years ago, and those individuals were shown to
be wrong by unparalleled decades of new achievement.
Those who say we cannot predict the future are correct
in one sense, in that we cannot say exactly what will be discovered over given
periods of time, or how these discoveries will affect the future direction
of research, as well as our everyday lives. We can however be confident that
these discoveries will be made, and with less certainty we can often predict
which individuals are likely to be most successful. These are those who have
made outstanding achievements in the past, and who can articulate what they
hope to do in the future. New discoveries will also arise from unanticipated
quarters, and given the opportunity new faces will continually join the leaders
in the field. While their discoveries will not necessarily be what they expect,
scientists have a much better record for clairvoyance than do the economists
or politicians, who expect others to produce on demand, while never having
to defend their own dismal records of prediction.
Some of the authors (Arnett) touch upon the subject
of chemophobia, the irrational fear and distrust felt by some of "chemicals".
This has led some chemical companies to drop the word chemistry from their
title or slogans. However equally prominent in the popular press are the uniformly
positive connotations of having "good chemistry", as applied to
movie stars, athletes, musicians, and a host of others. My favorite example
is a headline that a football coach was fired for "lack of chemistry",
as if this was a gaping void on his academic transcript. The message is that
there is widespread appreciation of the value of chemistry, and the public
realizes that there are risks and hazards associated with any worthwhile activity,
whether it be physical exercise or airline travel.
One theme found in many of the essays (Olah, Fox,
Bellus) concerns the value of physical organic chemistry in teaching scientists
to be problem solvers, and specific areas for emphasis in graduate research
that would be of value to industry and society are noted by Bellus. Arnett
notes the role played by chemistry conferences in education and in the spread
of knowledge and ideas. Chemistry journals, which have changed very little
in the past century, can also be expected to finally make a decisive move
away from printed paper as the major means of distribution.
Many of the authors, including Nefedov, Arnett, and
Breslow, note that computers, instrumentation, and electronics will have an
increasingly large role in the future. Biological chemistry is also sure to
increase in importance , as emphasized by Westheimer, Ingold, Breslow, Roberts,
and Mukaiyama. Gas phase chemistry, as discussed by Cacace and Schwarz, will
also continue as a major field of study, and will be particularly dependent
on improvements in instrumentation. This area will be of value for such diverse
topics as chemistry in space and organometallic synthesis. Time resolved spectroscopy
and matrix isolation are techniques that still provide valuable insights after
more than 50 years, and as emphasized by Houk, this will continue.
Linear free energy relationships began with the Brønsted
equation, and as noted by Engberts, Kosower, and Katritzky, these will be
increasingly useful, particularly as a way of systematizing the wealth of
data available from physical organic chemistry. This area will be of particular
utility in the pharmaceutical industry, and in the design of new materials.
Rather weak individual interactions such as hydrogen
bonding magnified by cooperative effects and solvation have decisive effects
in large systems, including biological organisms, and studies of these phenomena
will receive increasing emphasis in both computational and experimental investigations,
as noted by Roberts and Engberts. The formation of molecular assemblies may
be studied by gas-phase, solution, and theoretical techniques, and the merging
of these disciplines will receive increased attention in the future.
Reactive intermediates will continue to be studied,
including carbocations (Olah), free radicals (Ingold), and carbenes (Nefedov).
The study of free radicals, begun by Gomberg at the beginning of the Century
and pursued ever since by physical organic chemists, has proven to be of increasing
value in organic synthesis, biological mechanisms, spin labeling, and industrial
processes, particularly polymerization.
Organometallic chemistry is a rich ground for future
physical organic chemical investigations, and the state and promise of the
field has been ably and extensively summarized by Yamamoto and Schwarz. Much
of chemistry is about making things, and the physical organic chemist is involved
in this area, in the design and constuction of unusual and theoretically interesting
molecules, and also the deliberate study of molecular materials and supermolecules
(Breslow, Lahav, Mukaiyama). The role of mechanistic analysis in designing
new synthetic reactions will continue.
Houk traces the growth of computational and theoretical
organic chemistry from the 1960's, and most of the authors confidently expect
an ever-increasing emphasis on such studies. As discussed by Saveant, electrochemistry
is a powerful and convenient technique that offers rich rewards, and warrants
increased use, particularly in the study of electron transfer processes and
nonhomogeneous kinetics.
Kosower highlights the political and economic influences
on the practice of chemistry, and the need for greater sophistication in these
areas for chemists. Several of the authors (Arnett, Fox) note that students
trained in physical organic chemistry have favorable employment prospects
in industry, as they are experienced in problem solving. Others (Arnett, Engberts)
predict an increasing trend toward group, as opposed to single, investigator
research.
As noted by Arnett one of the greatest contributions
made by physical organic chemistry is the collection of simple qualitative
theories of broad applicability such as transition state theory, Hückel's
rules, the Woodward-Hoffmann rules, resonance, and hard-soft acid-base concepts.
These are ultimately the product of human intellect, however much assistance
is provided by large computers, sophisticated instrumentation, and diligent
laboratory work.
Finally there will be the unexpected, and as Mukaiyama
and others point out in the saga of the fullerenes, there are still limitless
opportunities for new discovery and surprise in the area of physical organic
chemistry.
