Masaru Ohsaku

An analysis of the through-bond interaction using the localized molecular orbitals with ab initio calculations—I : Lone-pair orbital interactions in cis- and trans-hydrazines

Abstract Ab initio SCF MO calculations using STO-3G basis set were performed on the cis- and trans- hydrazines. The cannonical MOs obtained by these calculations were then transformed into the localized MOs. With the use of the localized MOs thus obtained, the variation in the lone-pair orbital energies of the molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized MOs. As a result of this analysis, it was found that ; (a) the effect of the inner shell orbitais, l s electrons of N atoms, is not negligibly small, (b) the effect of the through-bond interaction is not so larger than the through-space interaction, and (c) the large contribution of the through-space interaction is caused from the indirect as well as direct interactions between two lone-pairs.

An analysis of the through-bond interaction using the localized molecular orbitals—II : Long-range proton hyperfine coupling in bridgehead alkyl radicals: bicyclo[1.1.1]pent-1-yl, bicyclo[2.1.1]hex-1-yl and bicyclo[2.2.1]hept-1-yl radicals

Abstract The INDO calculations were performed on three bridgehead alkyl radicals; bicyclo[1.1.1]pent-1-yl, bicyclo[2.1.1]hex-l-yl and bicyclo[2.2.1]hept-1-yl radicals. We have transformed the canonical molecular orbitals obtained by the INDO method into the localized molecular orbitals. With the use of the obtained localized molecular orbitals, the variation in the hyperfine coupling constant at the bridgehead proton in these radicals was pursued in terms of the through-bond (and/or the through-space) interaction according to the method by which we selectively can pick up a particular interaction between the specified localized molecular orbitals in a radical. As a result of this analysis, it was found that the hyperfine coupling constants in these radicals can be expressed by the summation of several terms; through-virtuals, through-space, through-bond, and some other coupling terms.

An analysis of the through-bond interaction using the localized molecular orbitals with ab initio calculations—II : Lone-pair orbital energies in bicyclo compounds: 7-azabicyclo[2.2.1]heptane and 2-azabicyclo[2.2.2]octane, and their n-methyl derivatives

Abstract Ab intio SCF MO calculations using STO-3G basis set were performed on 7-azabicyclo[2.2.1]heptane, N-methyl-7-azabicyclo[2.2.1]heptane, 2-azabicyclo[2.2.2)octane, N-methyl-2-azabicyclo[2.2.2)octane, and their model molecules. The orbital energies obtained by these calculations were compared with the experimental ionization potentials The canonical MOs obtained for the model molecules were then transformed into the localized Mos. With the use of the localized MOs thus obtained, the lone-pair orbital energies were pursued in the light of the through-space and/or the through-bond interactions between thw specified localized MOs. As a result of this analysis, it was found that the effects of the inner shell orbitals, 1s electrons of the N atom, and of the neighbouring N-C bonds of the skeleton (through-bond interaction) play a dominant role in the interaction with the lone-pair orbitals. It was also found that the effect of the N-Me group on the lone-pair orbital energy is considerably important.

A quantitative analysis of the through-space and the through-bond interactions between lone-pairs in azines: pyridazine, pyrimidine and pyrazine

Abstract The INDO calculations were performed on the three azines: pyridazine, pyrimidine, and pyrazine. The cannonical molecular orbitais obtained by these calculations were then transformed into the localized molecular orbitals. With the use of the localized molecular orbitals, the variation in the lone-pair orbital energies of these molecules were pursued in the light of the through-space and/or the through-bond interactions between the specified localized molecular orbitals in a molecule selectively. The interactions were expressed by the summation of several terms: through-space, through-bond, through-virtuals and coupling terms.

Electronic structures of collagen model polymers: (Gly-Pro)n, (Gly-Hyp)n, (Ala-Pro)n, (Ala-Hyp)n, (Gly-Pro-Gly)n, (Gly-Hyp-Gly)n, (Gly-Pro-Pro)n, and (Gly-Pro-Hyp)n

Abstract In order to investigate the relationship existing between the electronic structures of collagen and its biochemical functions in vivo, the semiempirical CNDO/2 SCF MO calculations were carried out on several model polymers of collagen, (Gly-Pro)n, (Gly-Hyp)n, (Ala-Pro)n, (Ala-Hyp)n, (Gly-Pro-Gly)n, (Gly-Hyp-Gly)n, (Gly-Pro-Pro)n and (Gly-Pro-Hyp)n. Geometries of the skeleton of these polymers were assumed to be the same as those of poly( l -proline) I (cis) and II (trans) and the calculations were performed only on infinite polymers in a single chain. The results show that the cis form is always more stable than the trans form for all the polymers treated. This energy difference between the cis and trans forms depends, for example, on the kind of amino acid residue, Gly or Ala, but this could not be seen in the Pro or Hyp residue. The flexibility or mobility of the collagen structure was explained using the energy difference between the cis and trans forms of the polymers, i.e. the cis-trans conversion of the collagen was discussed in connection with the energy difference. The reason why the collagen has the constitution of (Gly-Pro-Hyp)n is briefly discussed.

Molecular vibrations and force fields of alkyl sulfides—XIV. Infrared spectra of ethyl isopropyl, propyl isopropyl, butyl isopropyl and diisopropyl sulfides☆

Abstract Infrared spectra of ethyl isopropyl and propyl isopropyl sulfides were examined in the liquid and glassy states, and those of butyl isopropyl and diisopropyl sulfides were observed in the liquid and crystalline solid states. The spectra observed were assigned. Normal coordinates were treated. We have then discussed on the rotational isomers and molecular conformations for these sulfides.

An analysis of the through-bond interaction using the localized molecular orbitals—IV: Long-range proton hyperfine coupling in exo- and endo-hydrogens in bicyclo[2.1.1]hex-5-yl radical

Abstract The INDO calculations were performed on bicyclo[2.1.1]hex-5-yl radical. From these calculations, it was confirmed that the hyperfine coupling constants depend largely on the geometry of the α hydrogen. The localized MOs were obtained from the canonical MOs calculated by using the INDO method. With the use of the localized MOs thus obtained, the variation in the hyperfine coupling constants at the 6 exo - and 6 endo -protons in this radical was explained in terms of the through-bond and/or the through-space interactions according to the procedure which we proposed previously. That is by the procedure we can selectively pick up a particular interaction between the specified localized MOs. The hyperfine coupling constant in this radical can be expressed by the summation of several interaction terms. The difference in the hyperfine spin coupling constants of the H 6 exo and H 6 endo in the radical now concerned has been attempted to explain using MO coefficients of the occupied orbitals.

Reinvestigation of the molecular structures of some organo-sulfur compounds

Abstract The results of ab initio SCF MO calculations at the HF level on HSCH2SH, CH3SCH2SH, ClCH2CH2SH and HSCH2CH2SH using two kinds of basis sets, 3-21G and 3-21G + d(O.8C + 0.6S + 0.7Cl) are presented. Reasonable geometrical parameters for these molecules were reproduced by the latter set. Valuable information on rotational isomerism of these molecules is proposed. The barrier heights from the gauche to the trans forms in relation to the rotation around the CS and OC bonds are analyzed. The role of hydrogen bonding in governing the stable molecular geometry is discussed for CH3SCH2SH and ClCH2CH2SH.

CNDO/2 calculation of the relative stability of poly(γ-hydroxy-l-proline)

Abstract The CNDO/2 method using the tight-binding approximation for polymers was applied to poly(γ-hydroxy- l -prolines) (PHP). The calculations were carried out for PHPs which have the same backbone structure as those of poly( l -proline I) (Pro-I) and poly( l -proline II)(Pro-II). The results obtained show the preferred orientation of the OH group at the γ-position, which is in agreement with the experimental results. The calculations were also carried out for the B form (PHP-B). The conformational stability between the A form (PHP-A) and PHP-B was explained by using the calculated results in connection with the previous experimental and theoretical treatments. From the analysis of the total energy, the dominant stabilizing factors for the two forms are discussed.

A quantitative analysis of the through-space and the through-bond interactions between lone-pairs and σ-frames: S-triazine and S-tetrazine

Abstract The CNDO/2 and INDO calculations were performed on s-triazine and s-tetrazine. The s-triazine has three lone-pairs in a molecule, and these can be combined into three combinations, A, n s and n A . Among the three, n s and n A are degenerated when the whole interaction conserves its molecular point symmetry, D 3h . The s-tetrazine has four lone-pairs, which can be transformed into four combinations, SS,SA, AS and AA. The energies of these orbitals show interesting behavior. The results were subjected to an analysis from the standpoint of the through-space and through-bond interactions using the localized molecular orbitals. As a result of these analyses, the interactions were expressed by several interaction terms.