7301potentials to be included in intermolecular interactions studies, the ultimate goal toward which this model is directed.The usefulness of this approximate p(r) and their derived p e tentials in local density type mol& calculations will be analyzed in the near future. In this context, the inclusion of the model into efficient techniques for the decomposition of intermolecular interaction energies is one of the immediate problems to be treated. Related to this application, the estimation of intra-and intermolecular correlation effects by means of any suitable local density existing approximation with our analytic model p(r) will be also explored. This could permit a fast and easy computation of approximate correlation energies without basis set dependency problems.Acknowledgment. Financial support from the Spanish Direccion General de Investigacion Cientfica y Tecnica (DGICYT), under Grant No. PS89-0025, is gratefully acknowledged. References and Notes(1) Weinstein, H.; Politzer, P.; Srebenik, S. Theor. Chim. Acta 1975,38, 159. (2) Politzer, P.; Parr, R. G. J. Chem. Phys. 1976, 64, 4634. (3) (a) Schmider, H.; Sagar, R. P.; Smith, V. H. J. Chem. Phys. 1991,94, 8627. (b) Kohout, M.; Savin, A.; Preuss, H.Measurements of the temperature dependence of the Cotton-Mouton effects, together with the Rayleigh depolarization ratios and mean polarizabilities, of species in the series (CH2)2X, (CH3)2X, and C4H4X (X = 0, S) are reported and analyzed to yield optical-frequency (632.8 nm) principal polarizabilities of the relevant molecules. In addition, the previously developed 6-31G (+sd+sp) basis set is used to obtain SCF and MP2-level mean and anisotropic polarizabilities and also dipole and quadrupole moments for all nine molecules in the series (CH2)2X, (CHJ2X, and C4HJ (X = 0, S, Se). The results elucidate the electronic charge distributions in these molecules.

Measurements of the Rayleigh depolarization ratio of cyclohexane vapor at 441.6 nm, with rigorous exclusion of the spurious contribution from vibrational Raman scattering, are reported and analyzed to provide a reliable value of the polarizability anisotropy (lO^Act/C m2 V"1 = -1.93 ± 0.03) of this molecule. In addition, observations of the magnetic birefringence of the vapor and the field gradient birefringence of the liquid are interpreted in conjunction with the polarizability anisotropy to yield the magnetic anisotropy (1029 /3 T~2 = 19.2 ± 2.4) and the quadrupole moment (ÍO^Ó/C m2 = 3.0 ± 1.0) of cyclohexane. The anisotropy in the second moment of the electronic charge distribution and other fundamental electric and magnetic properties of cyclohexane are also evaluated and discussed.

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The composition of the copolymers of maleic anhydride (MA) with ethyl cinnamate (EC) and with anethole (ANE) polymerized in chloroform solutions with a radical initiator is reported. A strong alternating tendency is observed in the ANE-MA copolymer but EC is incorporated dominantly into the EC-MA copolymer. Both ANE and EC form 1 : 1 charge-transfer complexes with MA with the equilibrium constants determined to be 0,0845 and 0,026 L/mol, respectively. Applicability of the terminal, the penultimate and the complex participation models of the copolymerization mechanism is examined by non-linear least-square minimization technique using the most general forms of the composition equations. The complex participation model is found to be slightly in favor for both EC-MA and ANE-MA copolymerizations in CHC1,. 0 1991, Huthig & Wepf Verlag, Base1 CCC 0025-1 16X/91/$03.00

The monomer unit triad sequence distribution and the cidtrans linkage configurations at the cyclic maleic anhydride (MA) units in the copolymers of styrene (ST) and MA prepared in CCI, with AIBN at 50°C were quantitatively determined by 13C DEPT NMR spectroscopy. So much as 61 % of the linkages at the MA units were found to be in cis configuration, which was considered to be formed by a participation of the 1 : 1 electron donor-acceptor complex formed between ST and MA in the propagation step. The mole fraction of the cis configuration was found to be proportional to the mole fraction of alternating triad sequences when the monomer unit sequences approach to be completely alternating. This supported the proposal that, in alternating and semi-alternating copolymerizations, the alternating sequences were formed mainly by the addition of the complex. The equilibrium constant of the complexation in CCI, at 23°C was determined to be 0,21 L/mol.