Chemistry Reference
In-Depth Information
structural determination using predominantly mass spectrometry, NMR,
and, to a smaller extent, infrared spectrometry, allowed chemists to go,
typically in a week and sometimes in a single day, from an unknown
chemical in a mixture to a structure on paper. During the same period of
the 1960s, routine use of X-ray diffractometry
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for molecular structure
determination - the timescale was also the week -, at the hands of a few
pioneers such as R.B. Woodward started to rival the joint use of mass
spectrometry and NMR for the same purpose.
The 1960s were noteworthy too for the arrival of computation at the
service of the chemical laboratory, whether industrial or academic. At
that time, mainframe computers, housed in a computer center, were still
the norm. It was only later, in the 1970s and 1980s that personal com-
puters started to displace them. The introduction of the Macintosh by the
Apple company was the analog for computation of what the A-60 spec-
trometer had been for NMR: it enabled hands-on operation by the indi-
vidual graduate student. Developments of software were even more im-
portant than the steady, Moore-Law abiding, progress in hardware. Roald
Hoffmann introduced his Extended Hückel theory in 1963, implemented
in a molecular orbital program parametrized for many elements in the
Periodic Table. It allowed chemists to calculate properties such as ener-
gies and geometries for many chemical structures. Two years later, John
Pople came out with another semi-empirical tool for molecular orbital
calculations (Mulliken 1972, Ransil 1989), known by the acronym of
CNDO. At the same time, the Quantum Chemistry Program Exchange
(QCPE) was set-up in 1963 at the University of Indiana as a clearing-
house for software; many of the programs could be acquired by chemists
for a nominal fee. QCPE did much for the dissemination of molecular
orbital calculations as a new tool. Another highly significant develop-
ment, based on the computer too, was retrosynthetic analysis, by which
synthetic pathways to a target molecule could be identified and compared
(Corey 1992).
It would be an oversimplification to subsume under the heading of
'Big Science' (Weinberg 1967) the equipment of the chemical laboratory
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By tackling large biological molecules, pioneers from the British School initiated by
J.D. Bernal paved the way for such ultimately routine use (Hodgkin 1972).
