We have simulated the properties of an ensemble of biaxial particles interacting via an anisotropic pair potential, truncated at the second rank terms, using the Monte Carlo technique. The particles are confined to the sites of a face centred cubic lattice and the interactions are restricted to nearest neighbours. The system exhibits three phases in addition to the biaxial crystalline phase at absolute zero. There is a rotationally disordered (isotropic) phase followed by a uniaxi l rotationally ordered (nematic) phase which in turn becomes biaxial. ' he isotropic-nematic transitioff is found to be first order while the uniaxial-biaxial nematic transition is almost certainly second order. These observations confirm therefore the qualitative predictions of approximate theories of nematics formed by non-cylindrically symmetric particles. The quantitative agreement with certain of these theories for quantities, such as the order parameter and the transition temperature, is quite good.

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B3LYP/6-31G calculations account for the enhanced reactivity and endo stereoselectivity in the dimerization of the fleeting antiaromatic cyclopentadienone. Secondary orbital interactions promote endo stereoselectivity and a full merging of 4+2 and 2+4 allowed paths in an endo bispericyclic transition structure. Electrostatic effects increase reactivity and selectivity but the driving force to enhanced reactivity is the loss of antiaromaticity in the dimerization TSs while enhanced selectivity derives from the more efficient relief of antiaromaticity in the bispericyclic array.