The singlet potential energy surface of the M202 (M = Al, Ga, In, T1) system has been investigated using ab-initio electronic structure theory at the SCF, MP2, CISD, QCISD, and CCSD(T) levels and the density functional theory (for A1202 and Ga202). The results show that for A1202 and Ga202 accurate prediction of the relative stability of the various isomers can only be obtained at the correlated level using large oneparticle basis sets. At the CCSD(T)/TZ2P+f level, the most stable isomer of A1202 is a cyclic D2h form, whereas CISD and QCISD results indicate that the linear MOMO (C-J structure is the global minimum for Ga202. The results of ab-initio calculations with relativistic effective core potential also establish the linear MOMO geometry to be more stable (relative to the cyclic structure) for M = In, T1. The energy difference between the cyclic D2h form and the linear MOMO (C-J is less than 12 kcal/mol for all the systems studied.Theoretically predicted harmonic vibrational frequencies agree very well with the latest available experimental data.

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Interconversion of carbon sites in boat-chair-boat (BCB) cyclodecane occurs by way of the twist-boat-chair (TBC) conformation, which predicts that C-1 exchanges with C-4, etc. The previously obtained low-temperature 13C spectra could be matched by assuming (1,4) or (1,3) exchange, but not (1,2) exchange. A free-energy barrier of 5.54 kcal/mol was obtained for conversion of BCB to TBC at -137.4 degrees C. The major conformation of chlorocyclodecane and cyclodecyl acetate is assigned to the IIIe BCB.