th  - 1988 - 51st ENC Conference

'--- V 5 2 j INTERCONWERSION OF VALENCE TAUTO~RS IN
CYCLOBUTADIENE-LIC.~ [NAN &RGON MATRIX
~ Onmd~ B. P,. Arnold, J. G. Radziszewski, J. C. FaceUi, IC D. Malsch, H. Sumb, D. lvL Crank and J. Michl
Department of C3~¢mistry, Univer;ity of Utah, Sail Lake City, Utah 84112
The static 13C ]qMR dipolar spectrum of cyclobutadiene in an argon matrix is ~ . Vicinal]y 13C labeled
cyclobutadiene was generated photochemically fzom 1,2-13C2-cyclobutene-3,4.dJcart~xylic anhydride which wa
diluted in argon at a matrix ratio of about I:I00.
0
13 248 nm 13
"--"--- .,. • CO . C02
Ar 13
13 25K A 13
o B
Dipolar spectra of the p~'ursor, cyclobutadiene, and the dimer of cyclobutadiem were at] obtained.
Previous matrix isolation polarized IR specm)scopy results indicate that cyclobutadiene is either rotating in th(
matrix and/or interconverting between its two tautomers, A and B. Spectral mmuladons of the expected pauem for
the above cas~ as we].l as for the case of a nonmta~g noninterconverting molecule were completed. "Fnese simu.la-
fioas show that there is interconversion between the two valence mummers, A and B,which is at least comparable to
53 I
NMR CHEMICAL SHIFT ASSIGNMENTS BY ISOLATION OF
MOLECULAR CONFORMATIONS IN SOLUTION AT LOW TEMPERATURES.
PLATINUM- PHOSPHINE COMPLEXES: L. A. Luck*, C. H.
Bushweller, A. L. Rheingold, Department of Chemistry,
University of Vermont, Burlington, Vermont 05404
31p{IH} DNMR has been used to probe the stereodynamics of a series
of [(t-C~Hg:~2PR]2PtCl complexes. (R= CH3, C6H5, C6HsCH2, C2H5) In all
cases, below 150K, the spectra indicate as many as four sub-spectra (4
conformations). Assignment of the NMR peaks to specific conformations
has in the past been speculative. This poster will show how we solved
the dilemma. We will show how X-ray crystallographic data in
conjunction with isolation of specific conformations in solution at low
temperatures allowed unequivocal assignment of 31p{IH} NMR signals to
specific conformations.
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