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Dinitrogen activation in non-metallic systems has received considerable attention in recent years. Herein, we report the theoretical feasibility of N2 fixation using aminocarbenes (L) or their anionic derivatives. The molecular descriptors of L and anionic L‾, which affect the interaction of L and anionic L‾ with N2, were identified through multiple linear regression analysis. Additionally, the electron flow during C‒N bond formation was confirmed by performing intrinsic reaction coordination calculations with intrinsic bond orbital analysis for the reaction of anionic L‾ with N2.

In this study, we report the substituent effect on the structures, frontier orbital analysis, and spectroscopic properties (IR, 13C, 29Si NMR) in the molybdenum silylidyne complexes CpMo(CO)2(≡Si-para-C6H4X) (X = H, F, Cl, CN, NO2 , Me, OMe, NH2 , NHMe) using MPW1PW91 quantum chemical calculations. The calculated structural parameters and spectral parameters are compatible with the experimental values in similar complexes. The nature of the chemical bond between the [Cp(OC) 2Mo]− and [Si-para-C6H4X]+ fragments was explored with energy decomposition analysis (EDA). The percentage composition in terms of the defined groups of frontier orbitals for CpMo(CO)2(≡Si-para-C6H4X) complexes was investigated to explore the character of the metal–ligand bonds. The linear correlations between the properties and Hammett constants (σ p) were illustrated. Natural bond orbital analysis (NBO) was used to illustrate the electronic structure of the complexes.

We introduce Li+ involving cycloadditions between acetylene and ring-like cycloparaphenylenes (CPPs) in theory. Orbital analysis suggests an inverse electron-demand mechanism in which the diene CPP acts as an electron acceptor. Partial electron transfer to Li+ results in a reduced and localized π* orbital of CPP, giving rise to a site-selective reaction with a much smaller barrier.

In this comprehensive study on unsaturated phosphorus compounds of the type R-P=CR2, R-P=N-R, and R-P=P-R, we investigated how the electronic, spectroscopic, and geometric parameters are influenced by different substituents by means of ab initio and DFT methods. The parent systems are studied with highly accurate theoretical methods and used to benchmark DFT methods. The substituent effects are rationalized based on orbital analysis of DFT calculations for phos-phaalkenes, iminophosphanes, and diphosphenes in comparison with their analogous alkenes and imines. Theoretical data are also compared to experimental data if available. This study provides a broad picture of the use of DFT methods for unsaturated main group systems. Trends obtained from this study will enable a rational molecule design for selective manipulation of electronic and geometric properties.

This chapter deals with cheletropic reactions and higher order and multicomponent cycloadditions. The orbital mechanisms of cheletropic reactions are described and selection rules are provided. Singlet carbene cycloadditions including periselectivity and site selectivity, and cheletropic addition and extrusion of sulphur dioxide are presented. The cheletropic extrusions of nitrogen and carbon monoxide are also exemplified. Higher order cycloadditions involving more than 6 electrons are described which include 8-electron [4 + 4] photodimerizations and 10-electron [6 + 4] and [8 + 2] cycloadditions. The stereoselectivity of [6 + 4] cycloadditions has been shown mechanistically. Examples of cycloadditions involving more than 10 electrons including [14 + 2] cycloaddition are provided. Multicomponent cycloadditions with reference to [2 + 2 + 2] and [2 + 2 + 2 + 2] cycloadditions are described. Finally a frontier orbital analysis of cycloaddition involving more than two components is presented.

We report the synthesis and X-ray characterization of several oxaphosphirane tungsten(0) complexes especially designed to analyse the intramolecular W–CO(lone pair)⋯π(arene) interaction. The unexpected behaviour of this interaction in the solid state of oxaphosphirane complexes with different degrees of fluorination is rationalized by means of DFT calculations using orbital analysis and Bader's theory of “atoms-in-molecules”.

TcO3 + and TcO3(OH) along with their S and Se analogs, TcS3 +, TcSe 3 + ,TcS3(OH) and TcSe3(OH), have been analyzed employing the hybrid meta-GGA functional TPSS. Charge, geometry, frontier orbital analysis based on the optimized structure have been done as a function of type of an atom bonded to Tc. The effect of addition of OH− group to TcS3 +, TcSe 3 + and TcO3 + on geometrical and electronic properties is discussed. Rotational barrier of the O–H bond for title molecules are calculated and discussed.

The binding behaviors of eight bivalent metalloporphyrins (MPs) (MZn, Mg, Cu, Mn, Fe, Co, Ni, and Cd) with NH3 were investigated by density functional theory. For both MPs and corresponding complexes MPs-NH3, good linear correlations are found between the partial charge on metal M and that on atom N (nitrogen of porphyrin) as well as the MN bond length. Natural population and frontier orbital analysis demonstrate that charge transfer in CoP-NH3 is much easier and greater. As a consequence of the charge transfer and the hybridization of molecular energy levels, striking disparities of electronic properties of MPs-NH3 are observed. Particularly, a modest linear relationship is obtained between the magnitude of charge transfer and the binding energy. The much greater Fukui functions of CoP, together with its larger binding strength, suggest that CoP is more favorable to the interaction with NH3, which might be a promising sensing material to response NH3. © 2013 Wiley Periodicals, Inc.

The nature of the Ga-Ga bonding in Na2[Arx*GaGaArx*] (Arx* = C6H3-2,6-(C6H5)2) has been investigated and compared with that of in H2[Arx*GaGaArx*] using electron localization function (ELF) and orbital analysis. The calculation results show that in Na2[Arx*GaGaArx*], the Ga-Ga interaction is a non-classical triple bond, the heart of Na2[Arx*GaGaArx*] is the Ga2Na2 cluster rather than a simple Ga-Ga bond, and the contribution of the sodium atoms to the short Ga-Ga bond length is considerable. As the two sodium atoms are substituted by two hydrogen atoms, the Ga-Ga bond is replaced by two 3-center, 2-electron (3c-2e) Ga-H-Ga covalent bridged bonding.

We report results of hyperpolarizability calculations on CdnXn (X: S, Se and Te; n = 1–10) clusters. Our results show that the geometric configurations of different types of clusters under investigation are quite similar at specific values of n. Both static and frequency dependent components of first and second order hyperpolarizability tensors of CdnSn, CdnSen and CdnTen are compared. It is observed that in general nonlinear optical coefficients show identical variation in all the cluster materials. The present investigation also manifests the improvement of these coefficients due to the introduction of asymptotically correct generalized gradient approximation functional over the local density functional and normal gradient corrected functional. Symmetrized fragment orbital analysis has been performed to provide explanation of the observed hyperpolarizability variation. We also analyse how geometries with closely lying energy values influence the hyperpolarizabilities of these cluster materials.

Six groups of diastereomeric 2,4-disubstituted adamantanes were studied with DFT–GIAO–NBO (natural orbital analysis) methods. The calculated 13C chemical shifts reproduce well the experimental data. It was found that among all diastereomers, those bearing substituents in δ-syn-axial positions showed the largest overall deshielding, i.e. the sum of all 13C chemical shifts [Σδ(13C)] was the greatest and also had the highest delocalization contribution to the molecular energy evaluated with NBO. The higher delocalization energy is proposed to be the origin of the deshielding δ-syn-axial effect. Copyright © 2008 John Wiley & Sons, Ltd.

The reactions of 1-pentenyl decomposition system have been studied extensively at the B3LYP/6-311++G∗ ∗ level with Gaussion 98 package. The potential energy surface with zero-point energy correction was drawn. All reaction channels were fully investigated with the vibrational mode analysis, frontier orbital analysis and electron population analysis to confirm the transition states and reveal the reaction mechanism.

The equilibrium geometries, energies, harmonic vibrational frequencies, stability, and aromaticities for the [Formula: see text], E 4 Fe , and [ Fe (η4 - E 4)2]2- ( E = N, P, As, Sb, and Bi ) species are studied using density functional theory (DFT). The ground states of the E 4 Fe and [ Fe (η4 - E 4)2]2- systems are predicted to be Cs and D4d structures, respectively. Orbital analysis indicates that the orbital interactions between the π orbitals of the ligands and the atomic orbitals of the d 6 iron center are the main bonding scheme for these [ Fe (η4 - E 4)2]2- (D4d) complexes. The stability of the [ Fe (η4 - E 4)2]2- complexes exhibits the order P > As > Sb > Bi > N for E. On the basis of comparison with the known ferrocene, the NICS analysis confirms that the [ Fe (η4 - E 4)2]2- (D4d) as well as ferrocene are aromatic. The dissected NICS reveals that the aromaticities of the [ Fe (η4 - E 4)2]2- (D4d) are primarily attributed to the effects of their E–E π bonds and Fe lone pairs.

Density functional theory as well as Møller-Plesset investigations has been carried out on tetrafluoro cyclobutadiene, C4F4, to explore the origin of its nonplanarity. Although Petersson et al. (Petersson, E. J.; Fanuele, J. C.; Nimlos, M. R.; Lemal, D. M.; Ellison, G. B.; Radziszewski, J. G. J. Am. Chem. Soc. 1997, 119, 11122-11123) had earlier predicted a nonplanar geometry of this compound on the basis of spectral and bond orbital analysis, the explanation of the same from a more fundamental point of view is still missing. In the present study, we provide a heuristic explanation for the origin of nonplanarity of C4F4. The two major driving forces behind this nonplanar geometry are the unusual aromaticity of this cyclic homoatomic 4pi electron system and the second-order Jahn-Teller effect (SOJTE). These driving forces can well be explained by various energy and density parameters and also by nucleus-independent chemical shift (NICS) values. Aromaticity of a cyclic homoatomic 4pi electron system is quite remarkable. The enhancement of pi- delocalization as evidenced from molecular orbital analysis may be attributed to s-ppi mixing in nonplanar C4F4.

A detailed computational study is performed on the radical-molecule reactions between HCO/HOC and ethylene ( C 2 H 4) at the Gaussian-3//B3LYP/6-31G(d) level. For the HCO + C 2 H 4 reaction, the most favorable pathway is the direct C -addition forming the intermediate H 2 CCH 2 CHO , followed by a 1,2- H -shift leading to H 3 CCHCHO . Subsequently, there are two highly competitive dissociation pathways for H 3 CCHCHO : one is the formation of the direct H -extrusion product H 2 CCHCHO + H , and the other is the formation of C 2 H 5 + CO via the intermediate H 3 CCH 2 CO . The overall reaction barrier is 14.1 and 14.6 kcal/mol respectively, at the G3B3 level. The quasi-direct H -donation process to produce C 2 H 5 + CO with the barrier 16.5 kcal/mol is less competitive. Thus, only at higher temperatures, the HCO + C 2 H 4 reaction could play a role. In contrast, the HOC + C 2 H 4 reaction just need to overcome a small barrier 2.0 kcal/mol to generate C 2 H 5 + CO via the quasi-direct H -donation mechanism. This is suggestive of the potential importance of the HOC + C 2 H 4 reaction in combustion processes. However, the direct C -addition channel is much less competitive. The present kinetic data and orbital analysis show that the HCO radical has much higher reactivity than HOC , although the latter is more energetic. Till now, no kinetic study on the HOC radical has been reported, the present study can provide useful information on understanding the reactivity and depletion mechanism of the energetic HOC radical.

A complete orbital analysis of two isoelectronic complexes of trifluorobenzene (TFB), TFB ⋯ F − and TFB ⋯ Na + , as models for anion-π and cation-π interactions, respectively, has been performed at the MP2/6-31++G** level of theory. There are important orbital differences between both interactions, which are discussed in detail herein.

PM3 calculations were performed on the complexation of α-cyclodextrin (α-CD) with nitrobenzene, benzoic acid, benzoate anion, 4-nitrophenol, and 4-nitrophenolate anion. The results, in agreement with the experimental observations, indicated that the complex α-CD-benzoic acid was more stable than α-CD-nitrobenzene, and α-CD-4-nitrophenolate was more stable than α-CD-4-nitrophenol. Frontier orbital analysis suggested that charge-transfer interaction led to such behaviors, and hence constituted a nontrivial driving force in the molecular recognition of α-CD.

The ground-state conformations of 2-dialkylaminomethylphenol and 2-dialkylaminomethyl-4-methylphenol bearing two different coordination sites were analyzed by means of the semi-empirical AM1 method. Complexation of these ligands was investigated theoretically as boron and zinc complexes. Prevision of the possible bonding between the aminophenol ligands and the BF 2 + fragment was made using the frontier orbital concept. This concept was successfully extended to the prediction of the bonding with ZnCl 2 , showing theoretically that, in these cases, boron complexes can be safely used for modeling zinc complexes. The calculated ligand reactivity and the complex stability were in agreement with experimental results.

The application of missing-orbital analysis to molecular hyperpolarizability β obtained by a simplified sum-over-states calculation, allows one to study the effects of the π conjugation extension on both diagonal β zzz and off-diagonal β zxx components for C 2v molecules (the z -axis being the principal one). Extension of the z -length in aminonitropolyacetylenes by increasing the number of acetylene units increases β zzz but β zxx remains unchanged. Conversely, β zxx increases significantly with only a slight increase in β zzz if the π conjugation is extended mainly in the x -direction for 1,3-diamino-4,6-dinitrobenzene by replacing benzene with a fused-ring or inserting acetylene units between the substituents and benzene. These are ascribable to changes in the charge-transfer structure by the π extension.

The simplified sum-over-states (SOS) and missing-orbital analysis methods are introduced. The former aims to calculate the molecular polarizabilities in the framework of ab initio SCF theory, and the latter to analyze the calculated polarizabilities. The utility of the combination of these methods is demonstrated for the benzene derivatives, e.g. p -nitroaniline (PNA) and p -cyanoaniline (PCA). The calculated first-order hyperpolarizabilities (β) agree well with those of both CPHF calculations and experimental results. The missing-orbital analysis shows that β for PCA is contributed by both forward and backward charge transfer (CT) related to “out-of-plane” and “in-plane” orbitals, respectively. In contrast, β for PNA is confirmed to be explained fully by the conventional two-state model characterized by strong forward CT.

Geometry calculations were performed on pure BaCeO(3) fragments and on Y- and In-doped derivatives. HF and DFT approaches were used to investigate monoclinic and orthorhombic structures. The computational methods, structural models, and electronic structure investigation protocols were tuned taking into consideration and balancing the consistency of the results against the computational cost. The calculated structures and energetics parameter, as well as the detailed orbital analysis performed on the corresponding BaCeO(3) derivatives allowed us to explain experimental findings and to develop a procedure to study the cationic octahedral environment of doped X:BaCeO(3) (X = Y, In) and undoped BaCeO(3) protonic conductors useful to interpret experimental results and hopefully to design new experimental approaches. In detail, distances and angles of the studied materials are easily captured in the frame of the HF paradigm even by using low-level ECP basis sets. While, pure electronic-based approaches, involving the investigation of the Partial Density of States resulting from the C-Squared Population Analysis, show that the dopant species must leave unchanged, or even decrease, the local basicity of the oxygen octahedral environment in order to increase the conductivity of the BaCeO(3) derivatives. Whereas local structural changes that are not related to the basicity above affect to a less, if not null, extent the conductivity of the same derivatives.

After a general introduction to the current state of potential energy functions for delineating the steric requirements of exchange reactions, we proceed to a qualitative, Walsh-diagram-based orbital analysis of the preferred geometry approach to the barrier to such reactions. Extended Huckel calculations, perturbation theory, and a frontier orbital perspective are used to analyze the X+H 2

The 1,4-cyclization was studied in three model systems; formylketene, imidoylketene, and vinylketene, using ab initio MO methods. Structures of stationary points on the reaction potential energy surfaces were located at the HF/6-31G** level. Relative energies, estimated at the MP4SDQ/6-31G** level together with zero-point contributions, are as follows (in kcal/mol): formylketene (−17)→TS(4)→oxetone (0); imidoylketene (−10)→TS(15)→azetinone (0); and vinylketene (0)→TS(31)→cyclobutenone (0). The ring-opening of cyclobutenone is energetically more favorable than that of cyclobutene. The electonic reorganization accompanying the ring-closure of substituted ketenes was also examined using a localized orbital analysis. The process is found to be similar to the 1,5-cyclization of vinylazide and imidoylazide. Finally, the ketoketene-ketoketene rearrangement, including migration of a hydrogen in the formylketene, was considered

A theoretical quantum chemical study of the intramolecular hydrogen bonding interactions in 8-mercaptoquinoline has been carried out. Special attention has been paid to the rotation of S-H bond and intramolecular proton-transfer reactions. Therewith, the B3LYP/6-311++G(d,p), B3LYP/6-31+G(2d,2p), MPW1K/6-311++G(d,p), MPW1K/6-31+G(2d,2p), BHHLYP/6-311++G(d,p), and G96LYP/6-311++G(d,p) methods have been used. By means of the Onsager and PCM reaction field methods, the effects of solvent on hydrogen-bond energies, conformational equilibria, rotational barriers, and tautomerism in aqueous solution have been studied. These simulations were done at the MPW1K/6-311++G(d,p) and B3LYP/6-311++G(d,p) levels. Natural-bond orbital analysis has been performed to study the intramolecular hydrogen bond (IHB) in the gaseous phase and in aqueous medium. The stability of forms under consideration in solution does not coincide with that in the gaseous phase, underlining a great importance of the electrostatic influence of solvent. Double-proton transfer in the prototropic tautomerization of 8-mercaptoquinoline, one water molecule complex in the gaseous phase and in solution, has been systematically studied. The double-proton transfer occurs concertedly and synchronously. The water-assisted tautomerization is kinetically less, but thermodynamically more favorable, compared to that of the single-proton transfer. As in the case with single-proton transfer, for water-assisted reaction, the tautomerization energies and barrier heights decrease with the increase in dielectric constant, which implies faster and more complete tautomerization of 8-mercaptoquinoline in a polar solvent.

Analysis of optical spectra of a pseudo-para-dinitro[2.2]paracyclophane radical anion using Marcus-Hush theory reveals that its off diagonal coupling element, H(ab), is large enough, relative to its reorganization energy, to change it from a localized class II compound to a delocalized class III compound by changing solvents. The optical spectra, along with frontier orbital analysis, show that the assumption that E(op) = 2H(ab) for class III compounds is not true in this case.

Current-density maps were calculated by the ipsocentric CTOCD-DZ/6-311G** (CTOCD-DZ=continuous transformation of origin of current density-diamagnetic zero) approach for three sets of inorganic monocycles: S(4) (2+), Se(4) (2+), S(2)N(2), P(5) (-) and As(5) (-) with 6 pi electrons; S(3)N(3) (-), S(4)N(3) (+) and S(4)N(4) (2+) with 10 pi electrons; and S(5)N(5) (+) with 14 pi electrons. Ipsocentric orbital analysis was used to partition the currents into contributions from small groups of active electrons and to interpret the contributions in terms of symmetry- and energy-based selection rules. All nine systems were found to support diatropic pi currents, reinforced by sigma circulations in P(5) (-), As(5) (-), S(3)N(3) (-), S(4)N(3) (+), S(4)N(4) (2+) and S(5)N(5) (+), but opposed by them in S(4) (2+), Se(4) (2+) and S(2)N(2). The opposition of pi and sigma effects in the four-membered rings is compatible with height profiles of calculated NICS (nucleus-independent chemical shifts).

The molecular species 1,1- and 1,2-disubstituted alkenes have been used as model systems for a comparative discussion of the results obtained with quantitative orbital analyses using different fragmentation modes. It is shown that when indices of the overall energy effects are used, the results of a quantitative orbital analysis are independent of the chosen fragmentation mode. On the other hand, the results of such analysis can depend on the fragmentation mode when indices of partial energy effects are used.

One-electron properties calculated from SCF Xα SW/MT and near-HF functions for water are compared. A regional orbital analysis is used to assess the differences between the functions.

A perturbation molecular orbital treatment based on frontier orbitals is utilized to explain the selectivity order of a series of octyl, 1-methylheptyl, and benzyl derivatives toward m-chloroaniline and ethanol in a nucleophilic substitution reaction. The observed selectivity increases in the order ROSO2Ar < RCl < RBr < Rl. The model suggests that it is the differential HOMO–LUMO gap for a given substrate and the two reacting nucleophiles that governs substrate selectivity. Implications of this result to the reactivity–selectivity principle are discussed.

The results obtained in a quantitative orbital analysis of the ab initio SCFMO computations performed on hydroxylamine and thiohydroxylamine are described. The analysis is based on the use of fragment localized MOs and the energy effects associated with their interactions are estimated, in the framework of the ab initio SCF—MO computations, using PMO expressions. In particular the factors are analyzed which control the conformational preference in these molecules, and the effect of the sulphur 3d orbitals upon conformational stability is discussed.

Modern interpretations of coal structure all suggest that it possesses a molecular topology wherein sigma bonds invariably lie in close proximity either to aromatic π systems or to electro‐negative hetero‐atoms. We hypothesize that such a topology is well suited to the occurrence of concerted molecular reactions termed pericyclic which must therefore be intimately involved in all coal processing. Selected pericyclic reactions of model coal moieties are then examined by frontier orbital analysis. The reactions studied include hydrogen transfers, cope re‐arrangements, retro‐ene fragmentations, and cheleotropic extrusions, while the coal model substrates include α, ω‐diaryl n‐alkanes and α‐aryloxy, ω‐aryl n‐alkanes both with and without hydrogen donors such as molecular hydrogen and the two dihydronaphthalene isomers. The present results accord with the few experimental reactions reported with coal model compounds; further, the analyses indicate the frontier orbital interactions of greatest strength and prof...

Rotational barriers in BH3NH3 and CH3CH3 have been calculated using second-order perturbation theory by means of an ab initio bond-orbital method using experimental geometries and the Pople STO-3G basis. Although the electronic structure is quite different in the two molecules, comparative component analysis of the results (2.82 and 3.04 kcal mol–1 favouring staggered conformers) shows that for both molecules the barrier is due chiefly to vicinal interactions arising from exchange-overlap repulsion (penetration) between localized bonds having a closed-shell structure, supplemented for ca. 1/3 by electron delocalization between polarized bonds. The latter effect appears to be 10% larger in borazane than in ethane.

We describe the results obtained from quantitative orbital analysis, using ab initio SCF-MO computations, of the torsional isomerism of but-2-ene. The analysis is based on the use of σ fragment localized MOs and π fragment canonical MOs and the energy effects associated with their interactions are estimated using the quantitative Perturbational Molecular Orbital (PMO) and Total Energy approaches. It is found that conformational preferences in both cis- and trans-but-2-ene are determined by the π non-bonded interactions under matrix element control, while the trend in the relative stability of the two stable geometric isomers, tee > cee, is determined mainly by the difference in the steric repulsions between the σCH bond MOs of the two methyl groups.