Ethane hydrogenolysis on silica-supported tantalum hydride. Quantum-chemical study

The structures of the (H₄Si₂O₅)O₂Ta(R, RR"R, RR) clusters (R, R", R = H, Me, Et, Pr; R = CH₂), which model the basic structural units of the catalytic cycle of ethane hydrogenolysis on silica-supported tantalum hydride, were studied by the density functional theory (B3LYP) and the perturbation theory (MP2). The possible structure of active sites was proposed based on comparison of experimental results with calculated data. Ethane hydrogenolysis and metathesis proceed by a mechanism involving the formation of ethylene -complexes and carbenium derivatives of tantalum as intermediates.     

Micro determination of active hydrogen in organic compounds by lithium-aluminum hydride

Summary Roth's apparatus for the micro determination of active hydrogen according toZerewitinoff has been used to quantitatively estimate active hydrogen with the use of lithium-aluminum hydride. A suitable procedure has been evolved.

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Zusammenfassung DieRothsche Apparatur für die Mikrobestimmung nachZerewitinoff wird für die Bestimmung des aktiven Wasserstoffes mit Lithiumaluminiumhydrid verwendet. Dadurch wird der störende Einfluß von im Lösungsmittel und im Apparat etwa vorhandenen Feuchtigkeitsspuren vermieden.

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Résumé L'appareil deRoth pour le microdosage de l'hydrogène actif en accord avecZerewitinoff, a été utilisé pour doser quantitativement l'hydrogène actif par emploi de l'hydrure de lithium-aluminium. Un procédé convenable a été mis au point.

     

Quantum-chemical study of allylic and vinylic compounds of fifth-group elements

Energies and oscillator strengths of the long-wave electronic transitions for several conformers of allyl- and vinylamine and allyl- and vinylphosphine have been calculated by the semiempirical quantum-chemical MNDO method. The electronic structure of these molecules is discussed in detail, and the spectral and conformational effects ofn, and , conjugation are analyzed. Some suggestions concerning possible conjugation effects in the allylic compounds of As, Sb, and Bi are made.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1551–1554, September, 1993.     

Quantum-chemical study of nitrosonium complexes of monocyclic aromatic compounds

With the use of Hartree-Fock and DFT methods we demonstrated that for the benzene derivatives with the substituents Me, Et, Pr, i-Pr, t-Bu, CF₃, F, and Cl π-complexes are more favorable by energy, whereas with the substituents CHO, MeCO, PhCO, CN, NO, and NO₂ n-complexes are more feasible. The affi nity of aromatic compounds to the nitrosonium-cation (A_NO+) at the formation of the π-complexes grows with the growing donor character of the substituents in the ring and with their number. The best agreement between the calculated and experimental A_NO+ values for benzene was obtained with the use of RI-MP2/L1 method.     

Quantum-chemical study on nitrosonium complexes of Bi- and polycyclic aromatic compounds

The affinities of bi- and polycyclic aromatic compounds for nitrosonium ion (A_NO⁺ A_{NO^ + } ) were calculated at the RI-MP2/L1 and DFT/PBE/3z levels of theory. Both methods gave generally similar geometric parameters of nitrosonium complexes. The formation of pincer complexes in which the NO⁺ ion is linked to two aromatic rings is more energetically favorable than the formation of analogous complexes through external binding of NO⁺ to one aromatic ring. Linear correlations were found between the calculated A_NO⁺ A_{NO^ + } values of aromatic compounds and experimental equilibrium constants for the reactions of these compounds with nitrosonium ion in solution. Structural peculiarities of the examined nitrosonium complexes are discussed.     

Quantum-chemical study of allylic compounds with two bonded heavy atoms

It has been shown by the CNDO method that the bathochromic shift of the long-wave absorption band in the transition from allylstannane to compounds of the type C=C-C-Sn-X and C=C-Sn-X (where X is a heavy atom) is connected with the formation of a low-energy vacant *_S-X orbital, localized mainly in the region of the Sn-X chemical bond, and of an occupied _Sn-X orbital, the energy of which is somewhat higher than of the _C-Sn orbital. The dependence of the position of the long-wave absorbance region on conformation is related to the fact that, in planar and nonplanar conformers, the long-wave transitions are of a different type ( * and *, respectively); the bathochromic shift is determined to a large degree by the difference in the energies of the highest occupied MO ( - ) in the s-trans form. In the nonplanar conformers the heavy atom orbitals interact with the -orbital of the ethylene moiety through the bridge group; this leads to a significant delocalization of the HOMO and to a considerable change in its energy. On the other hand, their interaction with the *-orbital in compounds of the C=C-C-Sn-X type is very low and does not favor the delocalization of lower vacant MO. In vinyldistannane the *-orbital is noticeably delocalized, due to the interaction with the *_Sn-Sn orbital in planar and with the *_Sn-Sn orbital in nonplanar conformers.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 636–641, March, 1992.     

Quantum-chemical evaluation of the lability of π-electronic systems in n-benzoyl derivatives of phosphorus and sulfur imines

The charges on atoms, the bond indices, their components, and the energies of the highest occupied it orbitals of four N-benzoyl derivatives, of phosphorus and sulfur imines have been calculated by the CNDO/2 method in an spd basis. According to the results obtained, the system of a bridging sulfur-nitrogen group is more labile than a phosphorus-nitrogen group, in agreement with the experimental evaluations of the transmission of the electronic effects of substituents in these systems. An interpretation of this lability has been given.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 4, pp. 465–467, July–August, 1985.     

Parquet compounds on the basis of eight- and twelve-membered structure blocks: Quantum-chemical study

Annelated structures of cyclooctatetraene and cyclododecahexene and their expanded lowmolecular derivatives were studied using DFT B3LYP method with 6-311G(d,p), 6-311(df,p), 6-311+G(3df) basis sets. Monomer systems including planar antiaromatic cycles are stable in the singlet state, whereas the corresponding triplet states are significantly destabilized. The stability of nonstandard planar forms with antiaromatic cycles is provided by steric factors and the effects of π-electron interaction between the central and peripheral fragments.     

Quantum-chemical study on the mechanism of catalytic dimerization of norbornadiene in the presence of hydride nickel(I) complex

[2+2]-Cyclodimerization of norbornadiene to pentacyclic products with exo-trans(cis)-exo structure in the presence of model catalytically active η⁴-norbornadiene nickel hydride complex was simulated at the DFT/PBE level of theory. According to the calculations, the rate-determining step in the cyclodimerization process is reductive elimination of the metallacycle whose decomposition yields norbornadiene dimer. The formation of cis-dimer is unfavorable for both kinetic and thermodynamic reasons.     

Computational study of hydrogen bonding interaction between formamide and nitrosyl hydride

The hydrogen bonding interaction of formamide–nitrosyl hydride complex has been investigated using density functional theory (DFT) and ab initio method. The natural bond orbital (NBO) analysis and atom in molecules (AIM) theory were applied to understand the nature of the interaction. Two stable geometries are found on the potential energy surface, a six-membered cyclic structure of complex A and a seven-membered cyclic structure of complex B, characterized by AIM analysis. Complex A is less stable than complex B. It is confirmed that there are contractions of CH (compared with the monomer HCONH₂), NH bonds (compared with the monomer HNO) and the corresponding stretching vibrational frequencies are blue-shifted, while there is an elongation of the NH bond and the corresponding stretching vibrational frequency is red-shifted, relative to those of the monomer HCONH₂. From NBO analysis, it is evident that the electron densities in the σ^* (CH) and σ^*(NH) of the complex A are less than those of the monomers HCONH₂ and HNO, which strengthen CH and NH bonds. Furthermore, the increases in s-characters of X also strengthen XH bonds.     

The structures of the hydrogen halide salts of succinonitrile and related compounds

The constitutions of the hydrogen halide salts of succinonitrile are shown to be 2-amino-5,5-dihalo-1-pyrrolinium halides (II) and are thus the next lower homologs of the corresponding salts of glutaronitrile.¹ On the other hand the homologous 2,3-diphenyl-succinonitrile when treated with hydrogen bromide leads to 5-amino-2-bromo-3,4-diphenyl-3 -pyrrole hydrobromide (IX) which is tautomerically different from the analogous salt obtained previously from 2,5-diphenylglutaronitrile. The hydrolysis of IX has been examined and the products completely characterized. 2,2,3,3-Tetramethylsuccinonitrile in ether affords 5-imino-3,3,4,4-tetramethyl-2-pyrrolidone hydrobromide when treated with anhydrous hydrogen bromide whereas 1,1′-dicyano-1,1′-bicyclohexyl is unreactive towards this gas, in aprotic solvents.