The absorption spectra of nπ* and ππ* transitions in formaldehyde aqueous solution were studied by the reference interaction site model self-consistent-field (RISM-SCF) method. The electrostatic potential fluctuations acting on the solute sites originating from the solvent fluctuations were obtained by calculating the derivative of the solute-solvent radial distribution function analytically, and these were utilized to estimate the spectral bandwidths. The contribution from the solute vibrations was also examined. As a result, a blue shift of 1998 with bandwidth of 2987 cm−1 was obtained for the nπ* transition. The ππ* transition, on the other hand, showed a redshift of 1598 with the bandwidth of 5474 cm−1. The solvent fluctuation effect contributes to the bandwidths by 617 and 137 cm−1 for the nπ* and ππ* transition, respectively. We further analyzed the simulated absorption band shapes using effective charges on the atoms and the charge response kernel calculated for each state.

The free-energy pro®le for the Menshutkintype reaction NH 3 + CH 3 Cl 3 NH 3 CH 3 + Cl À in aqueous solution is studied using the RISM-SCF method. The eect of electron correlation on the free-energy pro®le is estimated by the RISM-MP2 method at the HF optimized geometries along the reaction coordinate. Solvation was found to have a large in¯uence on the vibrational frequencies at the reactant, transition state and product; these vibrational frequencies are utilized to calculate the zero-point energy correction of the freeenergy pro®le. The computed barrier height and reaction exothermicity are in reasonable agreement with those of experiment and previous calculations. The change of solvation structure along the reaction path is represented by radial distribution functions between solute-solvent atomic sites. The mechanisms of the reaction are discussed from the view points of solute electronic and solvation structures.

NBO-based CI/MP through-space/bond interaction analysis wasdeveloped to analyze specific orbital interactions under consideration of the effects of electron correlation. This treatment was applied to the analysis of stereoelectronic effects in S N 2 reactions of allyl bromide in which the effects of electron correlation play an important role (ammonia was used as the nucleophilic reagent). The S N 2 activation energy in allyl bromide is lower than that in propyl bromide, because both the -* and -* interactions in allyl bromide contribute equally to the stabilization of the transition state.

The elongation finite-field (elongation-FF) method is applied to calculate static (hyper)polarizabilities of π-conjugated chains, with donor and/or acceptor substituents, as well as a heterol block copolymer. Substituent effects on the linear polarizability (α) and second hyperpolarizability (γ) are modest, but a large first hyperpolarizability (β) can be induced. The dependence of β on chain length is rationalized on the basis of quasi-symmetry and donor/acceptor strength. Our copolymer consists of alternating blocks containing pyrrole rings and silole rings, which generates a quantum well. Copolymerization induces a fairly small β that oscillates in sign from block to block. The effect on α and γ is to enhance the contribution of the pyrrole blocks and diminish, by a larger amount, the contribution of the silole blocks.

Effect of the electronic polarization in solvent on the solvatochromic shift for the excitation energy of solute molecule is studied by the reference interaction site model self-consistent field (RISM-SCF) method. The electronic polarization in solvent molecule is represented by the charge response kernel (CRK) obtained by ab initio calculations. Employing the CRK, a charge polarizable RISM-SCF method is proposed for describing the electronic structure of solute molecules in solution and estimating the excitation energies. The excitation energy for nπ* transition of acetone is calculated in CH3CN, CHCl3, CCl4, and CS2 solvents and the solvent electronic polarization effect on the solvation shift is examined. As a result, a blue shifts of 1225, 675, 166, and 92 cm−1 is obtained in those solvents. Furthermore, the solvation shifts in the transitions to the 11B1, 11B2, and 21A1 states of pyridine are evaluated in the same solvents. A blue shift is observed for the 11B1 ← 11A1 transition in all the solvent, while the 21A1 ← 11A1 one shows a red shift.

Ab initio through-space/bond interaction analysis was applied to [3 + 2] annulation based on Brook rearrangement using beta-phenylthio-acryloylsilanes with alkyl methyl ketone enolates. An uncertain reaction mechanism, wherein a bulky cyclopentenol with large substituents on the same side of the five-membered ring was obtained as a major product, can be explained by the low activation energy of its reaction pathway. Intramolecular orbital interactions related to the carbanion generated by Brook rearrangement preferentially provide the stabilization of the reaction pathway to the bulky cyclopentenol (major product) compared with that provided to the non-bulky cyclopentenol (minor product). In addition, ab initio molecular orbital calculations suggest the existence of an E/Z conformational inversion after Brook rearrangement. This result accurately explains the loss of the E/Z stereochemical integrity in the starting materials of the experiment.

Interaction path analyses for pi-conjugated organic systems were performed at the ab initio molecular orbital level to examine the relationship between inter-radical interactions and the high-spin stability of the system. It was found that the high-spin stability results from through-bond interactions between radicals, not from through-space interactions, in relation to the stabilization of a low-spin state due to the effects of electron correlation. L(ij)(min) value for estimating the mixing of nonbonding molecular orbitals well predicted the relationship between the through-bond interactions and the high-spin stability. Furthermore, molecular orbital calculations revealed that the all-trans type interaction path between radicals produces long-range exchange interactions, and the additivity of high-spin stability is observed by keeping short-range through-bond interaction paths.

Two kinds of metal complexes, an achiral metal complex, [Fe(terpy)]2+ (terpy = 2,2‘,2‘ ‘-terpyridyl), and a chiral metal complex, Δ-[Ni(phen)3]2+ (phen = 1,10-phenanthroline), were coadsorbed by colloidally dispersed sodium saponite clay. Interaction between these molecules on a clay surface was investigated by electric dichroism and circular dichroism measurements. The molecular orientation of an adsorbed [Fe(terpy)]2+ ion was determined in the absence or presence of Δ-[Ni(phen)3]2+ by electric dichroism measurements. The angle of the C 2 axis of [Fe(terpy)]2+ with respect to a clay surface changed from 35.4° to 44.4° when the complex was coadsorbed with Δ-[Ni(phen)3]2+. The circular dichroism spectrum of a clay dispersion containing [Fe(terpy)]Cl2 and Δ-[Ni(phen)3]Cl2 was measured in the wavelength region of 350−600 nm. Δ-[Ni(phen)3]2+ had no electronic absorption in this region. Circular dichroism due to adsorbed [Fe(terpy)]2+ appeared when Δ-[Ni(phen)3]Cl2 was added to the ratio of [Fe(terpy)]Cl2/Δ-[Ni(phen)3]Cl2 from 1:1 to 1:3. The results were compared with the prediction by Kirkwood−Tinoco theory, in which circular dichroism is assumed to be induced by dipolar interaction with a chiral molecule.