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Encyclopedia of Physical Science and Technology EN009N-447 July 19, 2001 23:3

824 Microwave Molecular Spectroscopy

TABLE XIII (Continued)
Ar above furan plane shifted toward O Spycher, R. M., Hausherr-Primo, L., Grassi, G., and Bauder, A. (1995).
with respect to furan center of mass J. Mol. Struct. 351, 7

C 2v symmetry, triangular trimer Xu, Y., Jager, W., and Gerry, M. C. L. (1994). J. Chem. Phys. 100, 4171

C s symmetry, with terminal oxygens of Gillies, J. Z., Gillies, C. W., Lovas, F. J., Matsumura, K., Suenram, R. D.,
O 3 tilted toward axis of acetylene Kraka, E., and Cremer, D. (1991). J. Am. Chem. Soc. 113, 6408

a See also Novick, S. E., Leopold, K. R., and Klemperer, W. (1990). “Atomic and molecular clusters.” In “The Structures of Weakly Bond Complexes
As Elucidated by Microwave and Infrared Spectroscopy” (E. R. Bernstein, ed.), Chapter 3, Elsevier, New York.
slightly shortened compared to the opposite end of the monothioformic acid, HCOSH. In going from the trans to
benzene ring: the cis rotamer, the CSH and the HCS angles increase by
◦
◦
F more than 2 , whereas the OCS angle decreases by 3.4 .
˚
The SH bond length shortens by 0.02 A.
F 2 F
1 3 Similarly, subtle changes in structure which occur in
different isomers are illustrated for 3,3-difluoroacryloyl
fluoride in Fig. 17, where the C 3 C 2 C 1 and C 2 C 1 F 1 angles
Small changes in structural parameters in going from increase, while C 2 C 1 O decreases in going from the syn to
one rotamer to another may be illustrated by cis- and trans- the anti conformer.
Microwave spectroscopy has also provided direct ev-
idence as to the importance of intramolecular hydrogen

FIGURE 16 Calculated rotational constants of 7-oxabicyclo
[4.1.0] hept-3-ene for various values of the angle τ. τ measures
the displacement of atoms 3 and 4 out of the plane defined by
atoms 1, 2, 5, and 6. Positive values of τ correspond to the boat
form, negative values to the chair form. Observed rotational con-
stants (A, B, and C) are indicated by horizontal broken lines. The FIGURE 17 Conformers of difluoroacryloyl fluoride and structural
units of the rotational constants are GHz. The good agreement be- changes on syn–anti isomerization. For details of the analysis see
tween observed and calculated rotational constants for the boat Tam, H. S., Harmony, M. D., Brahms, J. C., and Dailey, W. P. (1991).
conformation established this as the correct form. J. Mol. Struct. 244, 59.