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Robert K. Bohn
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(b.
1939)
Visiting Professor, University of British Columbia,
1995
Visiting Professor, University of Michigan, 1987
Fellow of the Columbia Radiation Laboratory, Columbia
University, 1979
Visiting Scientist, University of Tokyo, 1971
NATO Postdoctoral Fellow, University of Oslo, 1964
Ph.D. Cornell University, 1964
B. S. , University of California, 1959
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We study problems in molecular structure. A few areas
of current interest are introduced below. The research
is predominantly experimental and the major technique
used is microwave rotational spectroscopy, often supplemented
by empirial force field or ab initio calculations
and with NMR or vibrational sepctroscopy. The experimental
work is carried out in two laboratories using the Stark
modulated microwave spectrometer in my laboratory and
the pulsed-jet Fourier Transform microwave spectrometer
housed at Wesleyan University in nearby Middletown.
Professor Stuart Novick of Wesleyan and I run the Southern
New England Microwave Consortium whose facilties include
the two spectrometers mentioned above. The facility
is used by both our research groups as well as other
visitors. The stimulation and international contacts
brought about by this research effort have been exceedingly
fruitful and exciting.
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Our research is guided by the hypotheses
that a potentially carcinogenic nitrosamine is incorporated
into a metabolic pathway by a structure-specific interaction
with a receptor not unlike the lock and key model in
enzyme-substrate binding, and that nitrosamines are
carcinogenic because they are mistakenly incorporated
into a biological pathway intended for the isoelectronic
amide. We have studied several nitrosamines and their
isoelectronic formamde analogues and find them to be
structurally extremely similar. Methyl ethyl nitrosamine,
a carcinogen, is shown. At present only one of the two
(and perhaps as many as four) conformers has been accurately
characterized. |
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Microwave spectroscopy has many advantages
over NMR spectroscopy for characterizing conformational
mixtures primarily because the two techniques have different
conformational lifetime requirements. Whereas NMR only
distinguishes conformers with fairly large potential
barriers separating them, there is essentially no lifetime
limit to conformers characterizable by microwave spectroscopy.
For example, we recently characterized the three conformers
of butyl cyanide. They appear as a single species in
NMR.
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The capability of microwave spectroscopy
to distinguish conformers separated by extremely low
potential energy barriers has not yet been exploited.
The triple bond in acetylene has a zero barrier to internal
rotation in the first approximation but probably has
a small but measureable barrier when substituted due
to long range steric and electronic effects between
the substituents. We have measured the rotational transitions
of the hexynone shown below and its interpretation awaits
the efforts of a bright and ambitious student. |
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