Conformers of gaseous protonated glycine

Ab initio geometry optimizations were performed on gaseous protonated glycine using the second-order Møller–Plesset perturbation theory with the 6-31G*, 6-31G**, 6-31+G**, and 6-311+G** basis sets. Eight energy minima and 12 saddle points in the low-energy region of the electronic potential energy surface were characterized. The global minimum was an amino N-protonated conformer containing an ionic H bond between the (SINGLE BOND)NH₃⁺ and O(DOUBLE BOND)C(DIAGONAL BOND)(DIAGONAL BOND) groups. The lowest energy O-protonated conformer was stabilized by a conjugative attraction between the nitrogen lone-pair electrons and the positively charged planar fragment (SINGLE BOND)C(OH)₂⁺. Relative electronic energies of the nine N- and 11 O-protonated species fall in the ranges of 0–10 and 30–40 kcal mol⁻¹. At room temperature the equilibrium distribution contained the most stable N-protonated conformer almost exclusively. Additional subjects for investigation include the effects of basis set and electron correlation on the predicted structures, nonbonded interactions that influence the relative stability of protonated conformers, conformational interconversions based on intrinsic reaction coordinate calculations, and kinetic pathways for protonation and associated changes in Gibbs free energy. The work provides geometric, energetic, and thermodynamic data pertinent to the study of gas-phase ion chemistry of amino acids and peptides. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1862–1876, 1998     

The structure of 1-chlorosilatrane: An ab initio molecular orbital and a density functional theory study

The molecular geometries of the 1-chloro-, 1-fluoro-, 1-methyl-, and 1-hydrogenosilatranes were fully optimized by the restricted Hartree-Fock (HF) method supplemented with 3-21G, 3-21G(d), 6-31G(d), and CEP-31G(d) basis sets; by MP2 calculations using 6-31G(d) and CEP-31G(d) basis sets; and by GGA-DFT calculations using 6-31G(d5) basis set with the aim of locating the positions of the local minima on the energy hypersurface. The HF/6-31G(d) calculations predict long (>254 pm) and the MP2/CEP calculations predicted short (∼225 pm) equilibrium Si(SINGLE BOND)N distances. The present GGA-DFT calculations reproduce the available gas phase experimental Si(SINGLE BOND)N distances correctly. The solid phase experimental results predict that the Si(SINGLE BOND)N distance is shorter in 1-chlorosilatrane than in 1-fluorosilatrane. In this respect the HF results show a strong basis set dependence, the MP2/CEP results contradict the experiment, and the GGA-DFT results in electrolytic medium agree with the experiment. The latter calculations predict that 1-chlorosilatrane is more polarizable than 1-fluorosilatrane and also support a general Si(SINGLE BOND)N distance shortening trend for silatranes during the transition from gas phase to polar liquid or solid phase. The calculations predict that the ethoxy links of the silatrane skeleton are flexible. Consequently, it is difficult to measure experimentally the related bond lengths and bond and torsion angles. This is the probable origin of the surprisingly large differences for the experimental structural parameters. On the basis of experimental analogies, ab initio calculations, and density functional theory (DFT) calculations, a gas phase equilibrium (r_e) geometry is predicted for 1-chlorosilatrane. The semiempirical methods predict a so-called exo minimum (at above 310 pm Si(SINGLE BOND)N distance); however, the ab initio and GGA-DFT calculations suggest that this form is nonexistent. The GGA-DFT geometry optima were characterized by frequency analysis. © 1996 by John Wiley & Sons, Inc.     

Estimates of the structure and dimerization energy of polyacetylene from ab initio calculations on finite polyenes

Ab initio calculations at the Hartree-Fock (HF) and the second-order Møller-Plesset (MP2) levels are performed for finite polyenes C_2nH_2n+2 to estimate the structure and dimerization energy (E_dim) of polyacetylene. The effect of electron correlation on the structure of finite polyenes is analyzed in detail. The MP3/6–31G* C(DOUBLE BOND)C and C(SINGLE BOND)C bond lengths in polyacetylene are estimated by a simple extrapolation method using empirical corrections for the MP2 deficiencies, yielding values [C(DOUBLE BOND)C(MP3) ∼ 1.36 Å and C(SINGLE BOND)C(MP3) ∼ 1.44 Å] that are in a good agreement with experiment (C(DOUBLE BOND)C (DOUBLE BOND) 1.36 Å and C(SINGLE BOND)C (DOUBLE BOND) 1.44–1.45 Å). Comparison is also made with other theoretical estimates of polyacetylene structure. E_dim is approximated by the energy difference between the equilibrium and hypothetical polyenic structures. It is estimated that E_dim is ∼ 1.4–1.5 kcal/mol (0.06–0.07 eV) per carbon-carbon bond at the HF level with 4–21G and 6–31G* basis sets and ∼ 0.3–0.5 kcal/mol (0.013–0.022 eV) at the MP2 level with the 6–31G* basis set. It is concluded that E_dim is very sensitive to the level of approximation employed so that a proper treatment of electron correlation is essential to obtain a reliable estimate of the dimerization energy. © 1997 John Wiley & Sons, Inc.     

Modeling properties of the HF dimer in argon clusters

We compare geometry configurations, vibrational properties, and electronic structures of (HF)₂ in a free state and inside argon atom shells Ar_n. For the first stage, molecular dynamics calculations for the (HF)₂ · Ar₆₂ heterocluster are performed with the help of model potentials HF(SINGLE BOND)HF, Ar(SINGLE BOND)Ar, and Ar(SINGLE BOND)HF. Then, ab initio quantum chemistry analysis is carried out for the smaller systems (HF)₂ · Ar₁₅ and (HF)₂ · Ar₆ when keeping the argon atoms closest to the trapped dimer. We conclude that the hydrogen-bonded complex (HF)₂ gains some extra stability inside the argon shells, originating primarily from a decrease of intermolecular distance R_FF. Electronic structure calculations are in accord with the changes in dynamical properties, namely, a noticeable increase in the vibrational frequency assigned to the F(SINGLE BOND)F stretching mode (+25 cm⁻¹) and decrease in rms deviations for the corresponding coordinate δ_FF. In addition to these changes, the argon atoms of the nearest solvent shell donate a small fraction of electron charge which is spent for an increase of population of the antibonding orbital σ^* of the free monomer unit and shift orbital energies primarily of the lone-pair fluorine species. These shifts are greater than the changes due to geometry alterations and the possible inaccuracies of the calculation scheme. © 1997 John Wiley & Sons, Inc.     

Synthesis and properties of polycarbosilanes with the meta-linkage bending unit by hydrosilylation polymerization

The polycarbosilanes (PCS) with meta-linkage bending unit ((SINGLE BOND)Me₂Si(SINGLE BOND)m(SINGLE BOND)C₆H₄(SINGLE BOND)Me₂Si(SINGLE BOND)CH₂CH₂(SINGLE BOND)) were successfully synthesized in mild conditions by hydrosilylation in the presence of [Pt{(CH₂(DOUBLE BOND)CHSiMe₂)₂O}₂]. The PCS obtained were soluble in various solvents owing to the lowering of the crystallinity. These properties are well compared with those of the PCS [(SINGLE BOND)Me₂Si(SINGLE BOND)p(SINGLE BOND)C₆H₄(SINGLE BOND)Me₂Si(SINGLE BOND)CH₂CH₂(SINGLE BOND)]_n. © 1996 John Wiley & Sons, Inc.     

Conformational analysis and rotation barriers of 2-aminoethanethiol and 2-aminoethanol: An ab initio study

All the possible rotamers of 2-aminoethanol and 2-amino-ethanethiol were fully optimized at the ab initio level using the 6–31G** basis with correlation energy inclusion and zero-point energy evaluation. Thirteen local minima for the former and 14 for the latter compound were found. In both molecules, the gauche′-gauche-gauche′ (g′Gg′) is the prevailing conformation, but in the sulfurated compound, it is accompanied by relevant percentages of other conformers, owing to the very low ΔE values. The stability of the g′Gg′ accommodation derives mainly from the presence of weak hydrogen bridges (O(SINGLE BOND)H···N and S(SINGLE BOND)H···N, respectively). The rotation barriers around the C(SINGLE BOND)C and C(SINGLE BOND)N bonds are higher than those around the C(SINGLE BOND)O and C(SINGLE BOND)S ones. © 1996 John Wiley & Sons, Inc.     

G2 ab initio calculations on three-membered rings: Role of hydrogen atoms

G2 ab initio calculations on all ABX three-membered rings (TMRs) that can be derived from cyclopropane by systematic substitution of the (SINGLE BOND)CH₂ groups by (SINGLE BOND)NH or (SINGLE BOND)O groups have been performed. Our results show that the decrease in the A(SINGLE BOND)B bond length as the electronegativity of X increases is significantly larger than that found for the corresponding acyclic analogs. In general, a systematic substitution of the (SINGLE BOND)CH₂ groups of cyclopropane by (SINGLE BOND)NH or (SINGLE BOND)O groups implies significant geometric changes that are not reflected in a parallel change of the corresponding conventional ring strain energy (CRSE). When the electronegativity of the groups forming the TMR increases the effect on the CRSE of the system is small, although the charge delocalization inside the ring decreases. The near constancy of the CRSE along the series can be explained in terms of the charge redistribution of the system where the (SINGLE BOND)CH₂ groups play a crucial role. There are, however, significant changes in the hydrogenation energies of the TMR investigated; our results show that, when in an ABX three-membered ring, the electronegativity of X increases the hydrogenation energy of A(SINGLE BOND)B bond decreases and vice versa. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1072–1086, 1998     

Ab initio studies of three-membered ring formation through intramolecular nucleophilic substitution

Three-membered ring (3MR) forming processes of ⁻X(SINGLE BOND)CH₂(SINGLE BOND)CH₂(SINGLE BOND)F and ⁻CH₂(SINGLE BOND)C((SINGLE BOND)Y)(SINGLE BOND)CH₂(SINGLE BOND)F (X(DOUBLE BOND)CH₂, O, or S and Y(DOUBLE BOND)0 or S) through a gas phase neighboring group mechanism (S_Ni) are studied theoretically using the ab initio molecular orbital method with the 6–31+G* basis set. When electron correlation effects are considered, the activation (ΔG^≠) and reaction energies (ΔG⁰) are lowered by ca. 10 kcal mol⁻¹, indicating the importance of the electron correlation effect in these reactions. The contribution of entropy of activation (−TΔS^≠) at 298 K to ΔG^≠ is very small, and the reactions are enthalpy controlled. The ΔG^≠ and ΔG⁰ values for these ring closure processes largely depend on the stabilities of the reactants and the heteroatom acting as a nucleophilic center. The Bell–Evans–Polanyi principle applies well to all these reaction series. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1773–1784, 1997     

Theoretical study of ester enolate–imine condensation route to β-lactams

The condensation reaction of the enolate of methyl acetate with formaldimine to afford a β-lactam was studied using the MP2-FC/6-31+G* level of theory taking into account the electrostatic effect of the solvent by means of a self-consistent reaction field continuum model. The reaction is a stepwise process with three main steps: the formation of the C3(SINGLE BOND)C4 bond, the closure of the β-lactam ring, and the elimination of the methoxide ion. The formation of the C3(SINGLE BOND)C4 bond is rate determining and according to our calculations is not a reversible step. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1826–1833, 1998     

Comparative study of BSSE correction methods at DFT and MP2 levels of theory

A comparative study of intermolecular potential energy curves is performed on the complexes H₂O(SINGLE BOND)HF, H₂O(SINGLE BOND)H₂O, H₂O(SINGLE BOND)H₂S, and H₂S(SINGLE BOND)H₂S using nine different basis sets at the MP2 and DFT (BLYP and B3LYP) levels of theory. The basis set superposition error is corrected by means of the counterpoise scheme and based on the “chemical Hamiltonian approach.” The counterpoise and CHA-corrected DFT curves are generally close to each other. Using small basis sets, the B3LYP functional cannot be favored against the BLYP one because the BLYP results sometimes get closer to the MP2 values than those of B3LYP. From the results—including the available literature data—we suggest that one has to use at least polarized-valence triple-zeta-quality basis sets (TZV, 6-311G) for the investigation of hydrogen-bonded complexes. Special attention must be paid to the physical nature of the binding. If the dispersion forces become significant DFT methods are not able to describe the interaction. Proper correction for the basis set superposition error is found to be mandatory in all cases. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 575–584, 1998     

An original route to poly[silylene-co-(2,4-disilapentane-2,4-diyl)] oligomers,efficient precursors of silicon carbide-based ceramics with variable C/Si ratios

Novel oligomers possessing a backbone formed of ((TRIPLE BOND)Si(SINGLE BOND)CH₂(SINGLE BOND)Si(TRIPLE BOND)) and (SINGLE BOND)Si(SINGLE BOND)_n units were prepared by the copolycondensation of bis(chlorosilyl)methanes and various dichlorosilanes in the presence of sodium, in refluxing toluene. The effect of the respective molar ratios of comonomers on the yields and the structure of the copolymers was investigated. The role of substituents on silicon atoms in the ability of these materials to provide convenient ceramic precursors upon pyrolysis was examined. When (TRIPLE BOND)Si(SINGLE BOND)H bonds were present, thermal cross-linking was readily performed and ceramics possessing variable C/Si ratios were prepared.     

π-Bonding contribution to restricted internal rotations in saccharides

Extensive semiempirical SCF-MO calculations confirm that the exo-anomeric effect in methyl O-, N- and S-glycosides deals with an interaction of π-character along the C₁(SINGLE BOND)Y₁ bond in a X₅(SINGLE BOND)C₁(SINGLE BOND)Y₁(SINGLE BOND)Me moiety (where X = O, S; Y = O, NH, S). The bond-order between orbitals of pπ symmetry on C₁ and Y₁ serves as a measure of all significant molecular orbital interactions responsible for the exo-anomeric stabilization. The set of simpler compounds X(SINGLE BOND)CH₂(SINGLE BOND)Y (X = OH, SH, SeH, TeH; Y = OH, SH, SeH, TeH, NH₂) on which the anomeric effect has been well studied was also calculated and it is noticeable that the π-bond-orders accord with the results of other analyses of the ab initio wave function accounting for the anomeric effect. Although the AM1 and the PM3 parameterizations of MNDO do not accurately reproduce the anomeric effect energetic, they do reproduce accordingly the expected variations in the molecular conformations of complex carbohydrates, and thus it follows that there are maximal π-bond-orders for the synclinal arrangement around the C₁(SINGLE BOND)Y₁ bond. In addition, the π-bond-orders show the same behavior for conformational preferences around the C₁(SINGLE BOND)C′₁ and the C₅(SINGLE BOND)C₆ bonds in methyl C-glycosides and in the hydroxymethyl group of α-D -glucose, respectively. © 1996 by John Wiley & Sons, Inc.     

Benzazole-N(SINGLE BOND)BH3 adducts. Reductive transposition of 2-benzimidazole, 2-benzothiazole,and 2-benzoxazole N(SINGLE BOND)BH3 adducts to 1,3,2-benzimidazaborole, 1,3,2-benzoxaborole,and 1,3,2-benzothiazaborole

1,3,2-Benzimidazaborole, 1,3,2-benzoxaborole, and 1,3,2-benzothiazaborole were synthesized from the corresponding 2-benzazole N(SINGLE BOND)BH₃ and 2-benzazole S(SINGLE BOND)BH₃ adducts through a reductive transposition from the isolobal fragment X(SINGLE BOND)C(sp²) (DOUBLE BOND) N(sp²) (SINGLE BOND) B(sp³) (X (DOUBLE BOND) N, O, S) to the fragment X(SINGLE BOND)B(sp²) (DOUBLE BOND) N(sp²) (SINGLE BOND) C(sp³). N(SINGLE BOND)BH₃ substitution shifts to lower frequencies 4-H, C-3a, and C-7a resonances. The X-ray diffraction analysis of 2-(o-methoxyphenyl)benzothiazole N(SINGLE BOND)BH₃ adduct is reported. Two new tetracyclic boron-bridged compounds were observed as by-products (6,9-(ethyl)-diaza-2-oxa-1-bora[3,4,7,8]-dibenzobycyclo[4.3.0]-nona-3,7-diene, 6d, and 8-aza-9-oxa-2-thia-1-bora-[3,4,7,8]dibenzobycyclo[3.4.0]nona-3,7-diene, 15d, when 2-(o-methoxyphenyl)-1-ethylbenzimidazole-BH₃ 6b and 2-(o-methoxyphenyl)-benzothiazole-BH₃ 15b adducts were heated. © 1996 John Wiley & Sons, Inc.     

Calculation of solvation free energy using RISM theory for peptide in salt solution

We developed a robust, highly efficient algorithm for solving the full reference interaction site model (RISM) equations for salt solutions near a solute molecule with many atomic sites. It was obtained as an extension of our previously reported algorithm for pure water near the solute molecule. The algorithm is a judicious hybrid of the Newton–Raphson and Picard methods. The most striking advantage is that the Jacobian matrix is just part of the input data and need not be recalculated at all. To illustrate the algorithm, we solved the full RISM equations for a dipeptide (NH₂(SINGLE BOND)CHCH₃(SINGLE BOND)CONH(SINGLE BOND)CHCH₃(SINGLE BOND)COOH) in a 1 M NaCl solution. The extended simple point charge (SPC/E) model was employed for water molecules. Two different conformations of the dipeptide were considered. It was assumed for each conformation that the dipeptide was present either as an un-ionized form or as a zwitterion. The structure of the salt solution near the dipeptide and salt effects on the solvation free energy were also discussed. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1724–1735, 1998     

Cyanide adsorbed on coinage metal electrodes: A relativistic density functional investigation

The adsorptive properties of cyanide (CN⁻) on coinage metal (M) electrodes (M=Cu, Ag, Au) have been investigated using a relativistic density functional method. The way to model the electrochemical potential applied to the electrodes is to consider the systems in the presence of a perturbative external field F. The field-perturbative approach is proven to be a suitable method in interpreting the observed spectral shifts with electrode potential. The calculated potential-dependent shifts of ω_{M(SINGLE BOND)CN} and ω_{C(SINGLE BOND)M} are similar for the three metals, in agreement with experiment observations. The relativistic effects are required to account for the similarity in the frequency shifts of ω_{M(SINGLE BOND)CN}. The calculated vibrational tuning rates dω_{C(SINGLE BOND)N}/dF are 6.61×10⁻⁷, 6.61×10⁻⁷, and 5.64×10⁻⁷ cm⁻¹/(V/cm) for M=Cu, Ag, and Au, respectively. The coupling of the M(SINGLE BOND)CN and C(SINGLE BOND)N internal modes contributes significantly (about 25%) to the size of the frequency shifts Δω_{C(SINGLE BOND)N} of the ligand. The effect of electric fields on the metal(SINGLE BOND)CN⁻ bonding is also investigated. It is shown that changes in the magnitude of CN⁻ to the metal donation and M(SINGLE BOND)CN bond strength occur under the influence of the electric field. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 175–185, 1998     

The hydroxyl radical reaction rate constant and products of ethyl 3-ethoxypropionate

The relative rate technique has been used to measure the hydroxyl radical (OH) reaction rate constant of ethyl 3-ethoxypropionate (EEP, CH₃CH₂(SINGLE BOND)O(SINGLE BOND)CH₂CH₂C(O)O(SINGLE BOND)CH₂CH₃). EEP reacts with OH with a bimolecular rate constant of (22.9±7.4)×10⁻¹² cm³ molecule⁻¹s⁻¹ at 297±3 K and 1 atmosphere total pressure. In order to more clearly define EEP's atmospheric reaction mechanism, an investigation into the OH+EEP reaction products was also conducted. The OH+EEP reaction products and yields observed were: ethyl glyoxate (EG, 25±1% HC((DOUBLE BOND)O)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl (2-formyl) acetate (EFA, 4.86±0.2%, HC((DOUBLE BOND)O)(SINGLE BOND)CH₂(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl (3-formyloxy) propionate (EFP, 30±1%, HC((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₂(SINGLE BOND)C((DOUBLE BOND)O)(SINGLE BOND)O(SINGLE BOND)CH₂CH₃), ethyl formate (EF, 37±1%, HC((DOUBLE BOND)O)O(SINGLE BOND)CH₂CH₃), and acetaldehyde (4.9±0.2%, HC((DOUBLE BOND)O)CH₃). Neither the EEP's OH rate constant nor the OH/EEP reaction products have been previously reported. The products' formation pathways are discussed in light of current understanding of oxygenated hydrocarbon atmospheric chemistry. © 1997 John Wiley & Sons, Inc.     

Theoretical study of metiamide,a histamine H2 antagonist

The requirements for H₂-antagonist activity so far identified for most of the known antagonists of histamine are the presence of a heterocyclic ring containing a basic center linked via a methylene chain to a substituted guanidine or thiourea polar side chain. Metiamide is a potent H₂ antagonist (pA2=6.06). We have used the ab initio Hartree–Fock (HF) method in order to study the conformational properties of the N₃(SINGLE BOND)H tautomers of metiamide molecule and histamine monocation. Three basis set (the 3-21G*, 6-31G**, and 6-31+G**) were used, the results compared, and the geometric parameters fully optimized. Our results indicate the preference of metiamide for a folded conformation with an intramolecular hydrogen bonding between the imidazole ring and one of the NH groups. The optimized geometrical parameters and charge distributions of both molecules, using the Mulliken, and natural bond order (NBO) analysis, are given and discussed. © 1998 John Wiley & Sons, Inc. Int J Quant Chem 69: 117–128, 1998     

Internal conrotation and disrotation in H2BCH2BH2 and diborylmethane 1,3 H exchange

The paths of correlated internal disrotation (barrier less than 0.4 kcal/mol) and conrotation (barrier around 1.9 kcal/mol) of the two BH₂ groups in H₂BCH₂BH₂ have been computed employing ab initio [MP2(full)/6–31G**] and density functional theory (Becke3LYP/6–311+G**) methods. Two B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative interactions stabilize the C_s symmetric H₂BCH₂BH₂ isomer ( 1 ). The B(SINGLE BOND)C(DOTTED BOND)B(p) hyperconjugative stabilization, evaluated by homodesmotic reactions and using the orbital deletion procedure (which “deactivates” the “vacant” born p orbital), is less than 6 kcal/mol in diborylmethane. The B(SINGLE BOND)C(DOTTED BOND)B(p) stabilization is shown to be remarkably large in C₄B₆H₁₀ (Td). At MP2(fu)/6–31G**, disproportionation into 1 and methane is only 5.6 kcal/mol exothermic. The 1,3 H exchange in diborylmethane is an asynchronous process and proceeds via a doubly bridged cyclic intermediate with 9.3 kcal/mol barrier. Structures with “planar tetracoordinate” carbon are stabilized considerably by BH₂ substituents, but they are still high in energy. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1792–1803, 1997     

A density functional study of Fe(SINGLE BOND)N2, Fe(SINGLE BOND)N+2, and Fe(SINGLE BOND)N−2

The interaction of an iron atom with molecular nitrogen was studied using density functional theory. Calculations were of the all-electron type and both conventional local and gradient-dependent models were used. A ground state of linear structure was found for Fe(SINGLE BOND)N₂, with 2S + 1 = 3, whereas the triangular Fe(SINGLE BOND)N₂ geometry, of C_2v symmetry, was located 2.1 kcal/mol higher in energy, at least for the gradient-dependent model. The reversed order was found using the conventional local approximation. In Fe(SINGLE BOND)N₂, the N(SINGLE BOND)N bond is strongly perturbed by the iron atom: It has a bond order of 2.4, a vibrational frequency of 1886 cm⁻¹, and an equilibrium bond length of 1.16 Å: These values are 3.0, 2359 cm⁻¹, and 1.095 Å, respectively, for the free N₂ molecule. With the gradient-dependent model and corrections for nonsphericity of the Fe atom, a very small binding energy, 8.8 kcal/mol, was calculated for Fe(SINGLE BOND)N₂. Quartet ground states were found for both Fe(SINGLE BOND)N⁺₂ and Fe(SINGLE BOND)N⁻₂. The adiabatic ionization potential, electron affinity, and electronegativity were also computed; the predicted values are 7.2, 1.22, and 4.2 eV, respectively. © 1997 John Wiley & Sons, Inc.     

The application of the density matrix method for the investigation of the trans-effect of heteroatom in σ-electron systems

The dependence of the intramolecular charge transfer through the σ-electron systems of substituted hydrocarbons on the spatial arrangement of the X(SINGLE BOND)C_α and C_β(SINGLE BOND)C_γ bonds has been studied using the perturbation theory for the one-electron density matrix (DM). Analytical expressions for the populations of the orbitals pertinent to the cis- and trans-bonds with respect to the X(SINGLE BOND)C_α bond have been obtained and analyzed. The Hamiltonian matrix elements determining the predominant direction of the above-defined charge transfer (cis or trans) have been revealed. The electron-accepting and electron-donating substituents (X) have been considered separately and the dependence of the resulting charge-transfer direction on the properties of substituent has been established. © 1996 John Wiley & Sons, Inc.