James M. Howell

Cyanogen isocyanate and dicyanoether: ab initio studies of geometries and electronic structures

Abstract Complete geometry optimizations, employing a minimal STO-3G basis set, have been applied to the recently-prepared cyanogen isocyanate [NCNCO] and to the isomeric dicyanoether [NCOCN]. Cyanogen isocyanate is found to be a rather flexible molecule with the computed barrier to inversion about the central nitrogen being ~5 k cal mol−1. In addition, the inversion motion is found to be coupled to the bending of the NCN and OCN linkages away from colinearity. On the other hand, dicyanoether is predicted to be a fairly rigid molecule, with no important inversion motions. Both molecules are predicted to have planar trans bent equilibrium structures similar to that found for the simpler HNCO-HOCN isomers. Cyanogen isocyanate is predicted to be the more stable isomer. Electronic structures of these molecules are discussed in the light of the results of a Mulliken population analysis.

Optimized Gaussian basis set for second row transition metals

A Gaussian basis set consisting of 12 s‐type, 8 p‐type, and 7 d‐type functions have been optimized for the second row transition metals (Y–Cd). Orbital energies along with the coefficients and exponents are presented for the neutral, monopositive, and dipositive atoms. Three additional s‐type functions were used to represent occupied 5s orbitals, when necessary.

Ab initio studies of methyllithium clusters

Ab initio self‐consistent field calculations with STO‐3, 4‐31, and 6‐31G basis sets are performed on methyllithium monomer dimer, trimer, and pentamer. The calculations provide data on binding energies and optimum geometries of various structures as well as indicate the formation of a lithium bond (between tetramers) similar to hydrogen bonds. Several tetrameric structures were investigated including one of D2d symmetry (resembling the ethyllithium tetramer) which is of possible importance in lithium exchange reactions.

The bent RC N linkage: An AB initio study of NH2CN, NF2CN and PF2CN

Abstract The ab initio energies, nuclear and electron repulsions and charge distributions have been calculated using moderately large basis sets as a function of the RC  N angle (R  NH 2 , NF 2 or PF 2 ). The optimum RC  N angles were calculated to be 178.9°, 176.6°, and 175° for NH 2 CN, NF 2 CN, and PF 2 CN, respectively. A rationalization of the differing bends is presented in terms of nuclear-nuclear and electron-electron repulsions.

A comparative ab-initio molecular orbital study of ammonia oxide and trifluoramine oxide

Abstract Geometry optimizations using various basis sets in the LCAO-SCF-MO method have been applied to F 3 NO and H 3 NO. Making use of the electronic wave-functions bonding is discussed in terms of donation from the oxygen lone pair into the N-F(H)o* orbitals and d-type orbitals on the nitrogen. Participation of d orbitals in the bonding is of modest importance for F 3 NO but not H 3 NO at least as far as the overlap population analysis is concerned.

Ab initio studies on several species of the formula X3YO and X3YOH

Ab initio molecular orbital calculations using both minimal and extended basis sets have been applied to two isoelectronic sets of molecules. One set corresponds to the 18 electron species H3NO, H3CO− and H3COH while the second set contains the 42 electron fluorinated molecules F3NO, F3CO− and F3COH. The geometries of these molecules have been optimized, using both the minimal STO-3G and the extended 4-31G basis sets. These comparative calculations reveal that the 4-31G basis produced structural parameters in much better agreement with experiment. The effect of includingd-orbitals in the basis set was also investigated. For the fluorinated oxides it has been found that the optimized 4-31G structures were only slightly altered by the addition ofd-orbitals. For H3NO, on the other hand, the inclusion ofd-orbitals considerably shortens the N-O bond distance. Both H3NO and CF3OH, which are unknown experimentally, are theoretically predicted to be capable of existence. The electronic structures of these molecules have also been examined using electronic partitioning according to the Mulliken scheme.

A theoretical study of some possible alkyllithium hexamers

Using ab initio SCF calculations we optimized three possible structures of hexameric methyllithium each having a near octahedral geometry of lithium atoms with capping methyl groups. The isomer in which the vacant faces of the octahedron are trans to each other is the most stable. The alternative structure with the vacant faces in apical contact is 8.8 kcal/mol (6-31G*//4-31G) higher in energy while the edge contact isomer is 26.3 kcal/mol more energetic than the trans structure. The methyl groups were found not to be faced centered. These results are rationalized electrostatically.

A Theoretical Study of Some Possible Fluxional Pathways for Alkyllithium Hexamers

We examined several possible fluxional pathways for hexameric alkyllithiums, performing ab initio SCF calculations on the model compounds octahedral Li6H6, Li6H4(CH3)2, and Li6(CH3)6. The lowest energy structures for these compounds had an approximately octahedral arrangement of the lithiums, with the H or CH3 ligands occupying six of the eight faces. The two empty faces were trans related. A concerted mechanism in which each of two ligands on opposite sides of the octahedron moves to an empty face was found to have a low energy barrier. The midpoint structures of this pathway for both Li6H6 and Li6H4(CH3)2 were symmetric or undistorted, whereas the midpoint structure for Li6(CH3)6 was quite distorted. These results are discussed in the light of similar findings on Li6 clusters. The adequacy of using 3-21G as a basis set for investigating alkyllithium geometries is also discussed.