James Kao

Assessment of isolated electronic effects on conformation. NMR analysis of nicotine and related compounds and ab initio studies of model compounds

Abstract The influence of electronegative substituents on the N ′-methyl group of nicotine upon the conformation of the pyrrolidine ring has been evaluated by the exact analysis of the high field 1 H NMR spectra of nicotine ( 1 ), N ′-ethylnornicotine ( 2 ), N ′-(2,2-difluoroethyl)-nornicotine ( 3 ) and N ′-(2,2,2-trifluoroethyl) nornicotine ( 4 ). The vicinal coupling constants for the pyrrolidine ring of 1–4 remain nearly constant, suggesting that as the electronegativity of the N ′-methyl substituent increases, only very small changes are seen for the C 3′ —C 4′ —C 5′ —N′ and the C 2′ —C 3′ —C 4′ —C 5′ dihedral angles. Substitution on the N ′-methyl group appears to have little effect on the orientation of the pyridyl ring with respect to the pyrrolidine ring. Ab initio calculations have been performed on the analogous 2-substituted diethylamines (diethylamine, N -ethyl-2-fluoroethylamine, N -ethyl-2,2-difluoroamine, and N -ehtyl-2,2,2-trifluoroethylamine) which constitute substructure models of 1–4 . These calculations confirm the NMR results in that they both indicate little, if any, effects on the rotational barriers and conformational energy profiles as a function of number of fluorine atoms.

S42+ and S42− : an ab initio study

Abstract The structures of S 4 2+ and S 4 2− have been investigated by ab initio calculations using the GAUSSIAN 70 system of programs and the 44-31G basis set. Electronic singlet states of the square form and three possible conformations of the chain structure were examined for both ions, and the singlet rectangle form of S 4 2− was also investigated. The anti chain form of S 4 2+ was found to be 78.3 kJ mol − more stable than the square form, in contrast to previous experimental data. S 4 2− is predicted to adopt the chain structure with the anti conformation.

An ab initio molecular orbital study of structures and energies of spirocompounds: spiro[3.3]heptane and spiro[3.3]hepta-1,5-diene

Abstract Ab initio molecular orbital theory with the STO-3G and 4-31G basis sets is used to determine the equilibrium geometries, enthalpies of formation, strain energies and spiro-interactions for spiro[3.3]heptane and spiro[3.3]hepta -1,5 - diene. For spiro[3.3]heptane, molecular mechanics calculations suggest that the component cyclobutane rings are puckered to a greater extent than in cyclobutane itself. For spiro[3.3]hepta - 1,5 - diene, STO-3G calculations predict that the component cyclobutene rings deviate slightly from an orthogonal arrangement. Spiro-interactions in spiro[3.3]hepta - 1,5 - diene are revealed by comparing the calculated structural parameters and strain energies with those of appropriate reference systems. The π-orbitals in spiro[3.3]hepta -1,5 -diene are predicted to be split by about 0.4 eV.

Theoretical studies of rotational barriers in 1,1′-biisoquinoline, 2,2′-biquinoline and substituted styrenes, alkenyl-naphthalenes, and alkyl-binaphthyls

Abstract Rotational functions of thirty-five compounds have been extensively and systematically studied by employing the molecular-orbital-based molecular mechanics (MOMM) approach. Various pathways have been examined and transition states identified. Comparisons were made between experimental and theoretical values for structures and rotational barriers. Hindered rotational transition-state geometries were calculated to be nonplanar, with significantly distorted aryl rings.

An interactive computer program to draw Newman projections

Abstract A generalized interactive computer program, NEWMAN, is described that draws quality Newman projections using various available graphics devices. NEWMAN