Jun-ichi Ishiyama

The conformation of α-(1→4)-linked glucose oligomers from maltose to maltoheptaose and short-chain amylose in solution

The conformation of maltose-type oligomers in water and in dimethylsulfoxide (Me2SO) was studied using two-dimensional NMR spectra. In Me2SO all of the oligomers have a 1a-type conformation. In water, they tend to adopt the same conformation, but the oligomers are looser and more flexible than in Me2SO.

Carbon-13 pulse fourier transform NMR spectra of substituted 1-methylcyclohexanols

Abstract 13C NMR spectra of a series of stereoisomeric substituted 1-methylcyclohexanols have been determined. The ring carbon resonances of the isomers having an equatorial OH group appeared at lower fields than those of the axial counterparts except the C-4 resonance of 1,2-dimethylcyclohexanol indicating an opposite trend. The signal of an axial Me group on C-1 appeared at a higher field than that of the equatorial counterpart; this is interpreted in terms of the γ-effect. Chemical shifts of ring carbons observed are compared with those predicted.

The conformational study of chitin and chitosan oligomers in solution

The inter-residual dihedral angles phi and phip of chitin and chitosan oligomers were determined from experimental 3J(C-H) constants and ROESY cross peaks.

New preparation technique for a highly dispersed nickel-alumina catalyst and its application to liquid phase hydrogenation

Abstract A highly dispersed nickel-alumina catalyst has been prepared by the sol-gel process using hydrous alumina sol derived from an aluminum salt solution. The size of the nickel particles is controlled by the dimensions of the network of the homogeneous precursor alumina gel. This new catalyst shows higher selectivity in the liquid phase hydrogenation of 1,3 and 1,5-cyclooctadiene and methyl linolenate than either Raney nickel or impregnated nickel-alumina catalysts. However, it shows lower activity than Raney nickel. This may be due to the tendency of the nickel particles to be encapsulated within the alumina particles.

n-π Interaction between an oxygen lone pair and π-electrons in cyclic allylic alcohols and ethers; carbon-13 nuclear magnetic resonance spectra, catalytic hydrogenation, and CNDO/2 calculations

In order to elucidate the n-π interaction between an oxygen lone pair and π-electrons, 13C n.m.r. spectra have been obtained for several cyclic allylic alcohols and ethers. The chemical shifts for sp2-carbons of these compounds are compared with those of the corresponding hydrocarbons. The chemical shift differences (Δδ) between compounds in which the oxygen atoms are placed at an anticlinal position with respect to the double bond and the corresponding hydrocarbons are different from those of a set of compounds, the oxygens of which are synperiplanar. We have also studied catalytic hydrogenation of and CNDO/2 calculations for these cyclic allylic compounds. These results are discussed in terms of homoconjugation

Carbon-13 nuclear magnetic resonance spectra of 3,7-disubstituted bicyclo[3.3.1]nonanes: conformation and through-space interaction

Carbon-13 n.m.r. spectra of several bicyclo[3.3.1]nonane derivatives were measured. The conformation of the framework of bicyclo[3.3.1]nonanes in this study was confirmed by the carbon chemical shifts. The π-electron delocalization was recognized in 3,7-dimethylenebicyclo[3.3.1]nonane and 7-methylenebicyclo[3.3.1]nonan-3-one due to the intramolecular through-space interaction between two π-orbitals.

THE STEREOCHEMISTRY OF REDUCTION PRODUCTS OF SANTONIN: EXAMINATION OF CONFORMATIONS BY MM2 CALCULATIONS

Since santonin has three kinds of hydrogenated parts, the assignment of the stereochemical structures for hydrogenated products is complicated and the details of the molecular framework have remained obscure. In order to examine the conformation of hydrogenated products of santonin, Molecular Mechanics (MM2) calculation was performed. The important information was obtained on the stereochemistry of tetra- and hexahydrosantonins and the formation mechanism of the reductive cyclization product was postulated by MM2 calculation results.

Proton, carbon, and phosphorus nuclear magnetic resonance and conformational studies on phosphate esters

The conformational free energies of phosphate and phosphoryloxymethyl groups on a cyclohexane ring were 0.94 and 0.88 kcal mol–1 in deuterium oxide at pD 5 and 0.20 and 1.09 kcal mol–1 in [2H6]dimethyl sulphoxide, respectively. For the rotational isomerism of the C–O axis of phosphate esters, 3JPH coupling constants indicate that the conformers with a planar trans arrangement of P–O and C(1)-CH2 bonds on primary phosphates or of P–O and C(1)–C(2 or 6) bonds on secondary phosphates predominated. The carbon magnetic shieldings in the vicinity of the phosphate ester function are interpreted in terms of an electronic exchange process.

Carbon-13 nuclear magnetic resonance spectroscopy of 1-tetralols and chroman-4-ols

13 C N.m.r. spectra of 1-tetralol, chroman-4-ol, and their substituted homologues have been determined. The CH(OH) resonances of 1-tetralol and chroman-4-ol indicate that their hydroxy-groups prefer a pseudoaxial orientation, as a result of A(1,2) strain. 13C N.m.r. spectra of stereoisomeric flavanols support the configurational relationship reported by Clark-Lewis et al. and by others that the α-isomer corresponds to the cis- and the β-isomer to the trans-form.