Naofumi Nakayama

Ab initio study of syn and anti structures of N-nitroso compounds containing a carbonyl group

Abstract A variety of ab initio molecular orbital methods, RHF, MP2 and B3LYP, have been applied to N-methyl-N-nitrosourea (1), N-methyl-N-nitrosoacetamide (2) and N-methyl-N-nitrosomethylcarbamate (3) and the anti and syn structures and the transition state (TS) structures connecting them have been examined. In each of these compounds, the anti structure was predicted to be more stable than the syn structure and the relative energy of the TS structure was considerably higher than those of the anti and syn structures. The energy difference between anti and syn of 1 is slightly smaller than those of 2 and 3 owing to the existence of hydrogen bonding between O in the nitroso group and H in the NH2 group.

Semiempirical calculation of electronic spectra of organic compounds by using the improved method of new-γ electron repulsion integral. Part 2. Polycyclic aromatic hydrocarbons (PAHs)

Excitation energies of 123 polycyclic aromatic hydrocarbons were calculated by incorporating the improved method of new-γ for the two-center electron repulsion integral into two semiempirical molecular orbital methods (CNDO/S and INDO/S). This variable method well reproduced experimental excitation energies of them. The average error of the improvement is about 0.162 (CNDO/S) or 0.237 eV (INDO/S) though the average error without the improvement is about 0.541 (CNDO/S) or 0.536 eV (INDO/S). The improvement was useful for the calculations of other organic compounds including hetero atoms, such as organic dye.

Semiempirical calculation of electronic spectra of organic compounds by using the improved method of new-γ electron repulsion integral

Electronic spectra of organic compounds were calculated by incorporating the improved method of New-g for the two-center electron repulsion integral into two semiempirical molecular orbital methods (CNDO/S and INDO/S). In this method we improved the previously reported New-g approximation by determining a parameter k for each bond. This method significantly improved the calculated wavelengths of linear polyenes obtained by using New-g: We further improved this by determining an expression for a variable k in which k is a function of the bond length of C ‐ C. This variable method well reproduced experimental electronic spectra of linear polyenes, toluene, xylene, styrene, and polyacenes. These results show that this variable method can be applied to the C‐ C bond in other organic compounds, such as polycyclic aromatic hydrocarbons (PAHs). q 2003 Elsevier B.V. All rights reserved.

Theoretical Electronic Circular Dichroism Study of 1,3-Diene Derivatives for the Elucidation of ECD Spectra of 1,3-Cyclohexadiene and Its Derivatives

The origin of P- or M-chirality of methyl substituted 1,3-cyclohexadienes are elucidated by time-dependent density functional theory (TD-DFT) calculation of 1,3-cyclohexadiene derivatives and acyclic 1,3-dienes. The sign-inversion of the rotatory strength of the lowest excited state between 1,3-cyclohexadiene and (5R)-axial-methyl-1,3-cyclohexadiene is caused by the conformation around the (C=)C-C(-Me) dihedral angle. The correlation between the sign of the rotatory strength and conformation has been found not only in methyl substituted derivatives but also fluoro substituted compounds.

Ligand Exchange Reaction on a Ru(II)–Pheox Complex as a Mechanistic Study of Catalytic Reactions

A ligand exchange of one of the acetonitrile ligands of the (acetonitrile)4Ru(II)–phenyloxazoline complex (Ru(II)–Pheox) by pyridine was demonstrated, and the location of the exchange reaction was examined by density functional theory (DFT) calculations to study the mechanism of its catalytic asymmetric reactions. The acetonitrile was smoothly exchanged with a pyridine to afford the corresponding (pyridine)(acetonitrile)3Ru(II)–Pheox complex with a trans orientation (C–Ru–N(pyridine)) in a quantitative yield, and the complex was analyzed by single-crystal X-ray analysis. DFT calculations indicated that the most eliminable acetonitrile is the trans group, which is consistent with the X-ray analysis. The direction of the ligand exchange is thus determined on the basis of the energy gap of the ligand elimination instead of the stability of the metal complex. These results suggested that a reactant in a Ru–Pheox-catalyzed reaction should approach trans to the C–Ru bond to generate chirality on the Ru center.