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Density functional theory (DFT) quantum chemical calculations of the structure and NMR parameters for highly strained hydrocarbon [2.2]paracyclophane 1 and its three derivatives are presented. The calculated NMR parameters are compared with the experimental ones. By least-squares fitting of the (1)H spectra, almost all J(HH) coupling constants could be obtained with high accuracy. Theoretical vicinal J(HH) couplings in the aliphatic bridges, calculated using different basis sets (6-311G(d,p), and Huz-IV) reproduce the experimental values with essentially the same root-mean-square (rms) error of about 1.3 Hz, regardless of the basis set used. These discrepancies could be in part due to a considerable impact of rovibrational effects on the observed J(HH) couplings, since the latter show a measurable dependence on temperature. Because of the lasting literature controversies concerning the symmetry of parent compound 1, D(2h) versus D(2), a critical analysis of the relevant literature data is carried out. The symmetry issue is prone to confusion because, according to some literature claims, the two hypothetical enantiomeric D(2) structures of 1 could be separated by a very low energy barrier that would explain the occurrence of rovibrational effects on the observed vicinal J(HH) couplings. However, the D(2h) symmetry of 1 with a flat energy minimum could also account for these effects.

The crystal structure of bismuth trichloride has been determined. Three-dimensional data were collected on a four-circle diffractometer using Mo K= radiation. The space group is Pn21a with orthorhombic cell a=7.641 (2), b= 9"172 (7), c= 6"291 (2)A. The final residual for the 935 observations is 4.43 %. The molecular structure consists of a bismuth atom closely associated with three chlorine atoms in the shape of distorted trigonal pyramid and with five other chlorine atoms at bridging distances. The geometry of this eightfold coordination is best described as a trigonal prism with six chlorine atoms at its comers, and with two more chlorine atoms in face-bridging positions. The three close Bi-C1 distances are 2.468, 2.513 and 2.518/~; distances to the bridging chlorines range from 3.216 to 3"450 A.

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