Multiple linear regression analysis and neural networks were employed to develop predictive models for Henry's law constants (HLCs) for organic compounds of environmental concern in pure water at 25 degrees C, using a set of quantitative structure property relationship (QSPR)-based descriptors to encode various molecular structural features. Two estimation models were developed from a set of 303 compounds using 10 and 12 descriptors, one of these models using two descriptors to account for hydrogen-bonding characteristics explicitly; these were validated subsequently on an external set of 54 compounds. For each model, a linear regression and neural network version was prepared. The standard errors of the linear regression models for the training data set were 0.262 and 0.488 log(H(cc)) units, while those of the neural network analogues were lower at 0.202 and 0.224, respectively; the linear regression models explained 98.3% and 94.3% of the variance in the development data, respectively, the neural network models giving similar quality results of 99% and 98.3%, respectively. The various descriptors used describe connectivity, charge distribution, charged surface area, hydrogen-bonding characteristics, and group influences on HLC values.

The lower-energy electronic states of a series of saturated sulfur compounds have been investigated theoretically and experimentally. The compounds investigated fell into two categories: the monosulfide series ABS in which the substituents A and B were varied, and the polysulfide series R2Sn, where n=1, 2, 3, and 4 and where R was usually CH3. The data collected included ultraviolet vapor spectra, solution spectra, solvent shifts, and vibrational data. Computations followed an approach related to that of Wolfsberg and Helmholz. This theoretical method closely approximates the experimentally observed energies in the compounds containing a single sulfur atom but encounters difficulties when two or more sulfurs are present because of the large 3dS−3dS and 4sS−4sS interactions which are predicted. It is indicated that the lower-energy excited electronic states of all the monosulfide compounds investigated are of a molecular nature in which the 4sS and 3dS atomic orbitals of sulfur play particularly dominant but by no means exclusive roles. The lower-energy excited states of the molecules R2Sn, n=2, 3, and 4, also contain significant 4s and 3d character; additionally, however, they are of S–S antibonding nature.

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Charge self-consistent semiempirical calculations, including all valence sigma orbitals of the ligands are reported for ferrocene, aminoferrocene, chloroferrocene, and nickelocene. The computations follow the Wolfsberg-Helmholz scheme, and use Slater atomic orbitals which mimic the overlaps, including distance dependence, of the SCF atomic orbitals. An attempt is made to assign electronic excitation energies in a manner consistent with computation and experiment. The only assignment which may be considered reasonably secure is that of the very intense absorption at 51 200 cm-1 which is taken to be the allowed component of the ela<--elu orbital excitation (f •• lclfob.=0.549/0.691). The ionizing orbital in ferrocene was found to be ala (-9.78 eV) and in nickelocene was el a (-6.874 eV). The formal charge on the metal was found to be positive in all cases. A discussion of metal-ligand bonding is included.1. Chern. Phys. 45, 2777 (1966.