Ab initio MO Calculations of benzene + TCNE and naphthalene + TCNE complexes with STO-3G π-split basis set

Ab initio SCF MO calculations have been carried out on benzene + TCNE (tetracyanoethylene) and naphthalene + TCNE complexes with the STO -3G, STO -3G π-split (STO -3G for π orbitals and a split basis for π orbitals), and 4–31G basis sets. The interaction energy, gross charges, dipole moment, and the electron density in the middle plane of the complexes have also been evaluated. The STO -3G π-split basis set is appropriate for the calculation of large π–π stacking complexes from two points of view, production of reliable results and ease of computations. The approximation scheme based on the semiorthogonalized orgitals is revealed to be very efficient to save CPU time and storage in such calculations. The stable conformation and the charge-transfer interaction of the two complexes are discussed on the basis of the calculated quantities.     

Ab initio calculation of the dipole polarizabilities of unsaturated hydrocarbons

Finite-field SCF MO calculations of polarizability are reported for ethene, benzene and naphthalene using three good gaussian basis sets Double-zeta wavefunctions yield values of α_LL and α_MM in agreement with experiment but the calculated α_NN is half the experimental value. Polarization functions when present preferentially improve α_NN. (L,M) and N refer to the molecular long, medium and normal axes, respectively.) STO-4G results are given for benzene, naphthalene, azulene, anthracene and phenanthrene, and the agreement with the experiment is reasonable after scaling the calculated α_LL and α_MM by a constant factor. The calculated α_MM are an order of magnitude too low.     

Oxidative addition of dihydrogen to (eta6-arene)Mo(PMe3)3 complexes: origin of the naphthalene and anthracene effects

In contrast to the benzene and naphthalene compounds (eta(6)-PhH)Mo(PMe(3))(3) and (eta(6)-NpH)Mo(PMe(3))(3), the anthracene complex (eta(6)-AnH)Mo(PMe(3))(3) reacts with H(2) to undergo a haptotropic shift and give the eta(4)-anthracene compound (eta(4)-AnH)Mo(PMe(3))(3)H(2). Density functional theory calculations indicate that the increased facility of naphthalene and anthracene to adopt eta(4)-coordination modes compared to that of benzene is a consequence of the fact that the Mo-(eta(4)-ArH) bonding interaction increases in the sequence benzene < naphthalene < anthracene, while the Mo-(eta(6)-ArH) bonding interaction follows the sequence benzene > naphthalene approximately anthracene.     

Theoretical studies on the conformations and properties of phenylazonaphthalenes

The conformations of phenylazo‐2‐naphthalene (I) and phenylazo‐1‐naphthalene (II) have been studied using ab initio methods and density functional theory. The rotational potential energy surfaces about the C N bonds were calculated for both the trans and the cis forms at the PM3 and HF/STO‐3G levels. The PM3 method was found to be incapable for locating the energy minima correctly. The geometries of rotamers obtained from the HF/STO‐3G surface were fully optimized at the HF/6‐31G* and B3LYP/6‐31G* levels. Single‐point MP2/6‐31G* calculations have also been carried out at the HF/6‐31G* geometries. The vibrational spectra, standard thermodynamic functions, heats of formation, and equilibrium molar fractions have been obtained. According to the calculated results, I is comparatively more stable than II. The trans forms have much lower energies than the cis forms, implying that I and II mainly exist in the trans planar forms. The energy gap (ΔE) between the frontier molecular orbitals (MOs) of the cis forms are about 0.7 eV higher than those of the trans ones, indicating that change in geometry from trans to cis form will cause a hypsochromic effect. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 25–33, 2000     

The formation of naphthalene, azulene, and fulvalene from cyclic C5 species in combustion: an ab initio/RRKM study of 9-H-fulvalenyl (C5H5-C5H4) radical rearrangements

Chemically accurate ab initio Gaussian-3-type calculations of the C(10)H(9) potential energy surface (PES) for rearrangements of the 9-H-fulvalenyl radical C(5)H(5)-C(5)H(4) have been performed to investigate the formation mechanisms of polycyclic aromatic hydrocarbons (PAHs) originated from the recombination of two cyclopentadienyl radicals (c-C(5)H(5)) as well as from the intermolecular addition of cyclopentadienyl to cyclopentadiene (c-C(5)H(6)) under combustion and pyrolytic conditions. Statistical theory calculations have been applied to obtain high-pressure-limit thermal rate constants, followed by solving kinetic equations to evaluate relative product yields. At the high-pressure limit, naphthalene, fulvalene, and azulene have been shown as the reaction products in rearrangements of the 9-H-fulvalenyl radical, with relative yields depending on temperature. At low temperatures (T < 1000 K), naphthalene is predicted to be the major product (>50%), whereas at higher temperatures the naphthalene yield rapidly decreases and the formation of fulvalene becomes dominant. At T > 1500 K, naphthalene and azulene are only minor products accounting for less than 10% of the total yield. The reactions involving cyclopentadienyl radicals and cyclopentadiene have thus been shown to give only a small contribution to the naphthalene production on the C(10)H(9) PES at medium and high combustion temperatures. The high yields of fulvalene at these conditions indicate that cyclopentadienyl radical and cyclopentadiene more likely represent significant sources of cyclopentafused PAHs, which are possible fullerene precursors. Our results agree well with a low-temperature cyclopentadiene pyrolysis data, where naphthalene has been identified as the major reaction product together with indene. Azulene has been found to be only a minor product in 9-H-fulvalenyl radical rearrangements, with branching ratios of less than 5% at all studied temperatures. The production of naphthalene at low combustion temperatures (T < 1000 K) is governed by the spiran mechanism originally suggested by Melius et al. At higher temperatures, the alternative C-C bond scission route, which proceeds via the formation of the cis-4-phenylbutadienyl radical, is competitive with the spiran pathway. The contributions of the previously suggested methylene walk pathway to the production of naphthalene have been calculated to be negligible at all studied temperatures.     

Formation of Azulene‐Embedded Nanographene: Naphthalene to Azulene Rearrangement During the Scholl Reaction

Incorporation of a non‐hexagonal ring into a nanographene framework can lead to new electronic properties. During the attempted synthesis of naphthalene‐bridged double [6]helicene and heptagon‐containing nanographene by the Scholl reaction, an unexpected azulene‐embedded nanographene and its triflyloxylated product were obtained, as confirmed by X‐ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring‐fused substructure containing two formal azulene units is formed, but only one of them shows an azulene‐like electronic structure. The formation of this unique structure is explained by arenium ion mediated 1,2‐phenyl migration and a naphthalene to azulene rearrangement reaction according to an in‐silico study. This report represents the first experimental example of the thermodynamically unfavorable naphthalene to azulene rearrangement and may lead to new azulene‐based molecular materials.     

Gas-phase ion/molecule reactions between dimethoxyphosphonium ions and aromatic hydrocarbons

Ion/molecule reactions between O=P(OCH(3))(2)(+) phosphonium ions and six aromatic hydrocarbons (benzene, toluene, 1,2,4-trimethylbenzene, naphthalene, acenaphthylene and fluorene) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2)(+) phosphonium ions, formed by electron impact from neutral trimethyl phosphite, were found to react with aromatic hydrocarbons (ArHs) to give (i) an adduct [ArH, O=P(OCH(3))(2)](+) and (ii) for ArHs which have an ionization energy below or equal to 8.14 eV, a radical cation ArH(+ *) by charge transfer reaction. Collision-induced dissociation experiments, which produce fragment ions other than the O=P(OCH(3))(2)(+) ions, indicate that the adduct ions are covalent species. Isotope-labeled ArHs were used to elucidate fragmentation mechanisms. The charge transfer reactions were investigated using density functional theory at the B3LYP/6-311 + G(3df,2p)//B3LYP/6-31G(d,p) level of theory. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2)(+) and benzene is described.     

Theoretical Studies of Azulene and Its Derivatives

The results of ab initio calculation with STO-3G and 6-31G basis set on the azulene and its derivatives (included azulenequinones, diazoazulenequinones and polyether bridged azulenes) are presented in accordance with considerations of structures and bonding. Azulene is a nonalternant aromatic compound with ten π electrons and it has either C_s or symmetry dgpend on the different carbon and carbon bonding. The calculation results indicate that C_s symmetry is the ground state structure of azulene. TTie simple MO and CIS calculations describe the excited state of azulene.     

NIR-Absorbing π-Extended Azulene: Non-Alternant Isomer of Terrylene Bisimide

The first planar π-extended azulene that retains aromaticity of odd-membered rings was synthesized by [3+3] peri-annulation of two naphthalene imides at both long-edge sides of azulene. Using bromination and subsequent nucleophilic substitution by methoxide and morpholine, selective functionalization of the π-extended azulene was achieved. Whilst these new azulenes can be regarded as isomers of terrylene bisimide they exhibit entirely different properties, which include very narrow optical and electrochemical gaps. DFT, TD-DFT, as well as nucleus-independent chemical shift calculations were applied to explain the structural and functional properties of these new π scaffolds. Furthermore, X-ray crystallography confirmed the planarity of the reported π-scaffolds and aromaticity of their azulene moiety.     

Ring-current aromaticity in open-shell systems

The ab initio ipsocentric approach to calculation and mapping of induced orbital current density is extended to open-shell π systems. ROHF/6-31G^** calculations document the (magnetic) aromaticity of planar 4nπ triplet states of 4π/8π annulenes and isobenzofulvene, and quintet excited-state azulene. An orbital model for currents rationalises the generalised form of Baird’s rules, by which 4n + 2 annulenes are aromatic (antiaromatic) in states of even (odd) total spin (vice versa for 4nπ annulenes). In contrast to geometric criteria, ring-currents predict antiaromaticity for the doublet naphthalene radical anion.     

NIR‐Absorbing π‐Extended Azulene: Non‐Alternant Isomer of Terrylene Bisimide

The first planar π‐extended azulene that retains aromaticity of odd‐membered rings was synthesized by [3+3] peri‐annulation of two naphthalene imides at both long‐edge sides of azulene. Using bromination and subsequent nucleophilic substitution by methoxide and morpholine, selective functionalization of the π‐extended azulene was achieved. Whilst these new azulenes can be regarded as isomers of terrylene bisimide they exhibit entirely different properties, which include very narrow optical and electrochemical gaps. DFT, TD‐DFT, as well as nucleus‐independent chemical shift calculations were applied to explain the structural and functional properties of these new π scaffolds. Furthermore, X‐ray crystallography confirmed the planarity of the reported π‐scaffolds and aromaticity of their azulene moiety.     

The impact of basis set superposition error on the structure of π?π dimers

The effect of basis set superposition error (BSSE) on the structure and energy of benzene, naphthalene, corannulene, and sumanene dimer has been analyzed. MP2 method was chosen and the effect is estimated using 6‐31G, 6‐31G(d), 6‐311+G(d), cc‐pVDZ, and cc‐pVTZ basis sets. The model calculations on benzene dimer indicate that the impact of BSSE on the equilibrium geometry of π‐stacked dimers appears to be quite significant. Calculations on larger molecular dimers such as the dimers of naphthalene, corannulene, and sumanene are also studied. The practical implication of the current observation on modeling the macromolecular structure is discussed. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Ab initio calculations of guanidinium–carboxylate interaction

Ab initio calculations (self-consistent-field Hartree–Fock) using 6-31G and STO -4G basis sets are used to investigate the interaction between guanidinium and methylguanidinium ion with the carboxylate group of formate. Binding energies and optimum geometries are obtained and compared with reported results using a smaller basis set (STO -3G). The importance of this interaction in proteinsubstrate binding is discussed.     

The methyl isocyanide isomerization: A CNDO/2 study with partitioning of energy

Ab initio LCAO MO SCF calculations have been carried out to predict core electron binding energies and shifts in fluoro- and chloro-methanes. The quality of the calculations ranges from a better than double zeta basis set to minimal STO (3 G) basis set. Predictions of binding energies and shifts are made using Koopmans' theorem, hole state calculations and equivalent cores calculations. Using a flexible basis set there is very little difference in the prediction of shifts by these three methods but for minimal basis set calculations the equivalent cores calculations give the best results.     

Synthesis and two-electron redox behavior of diazuleno[2,1-a:1,2-c]naphthalenes

The Diels-Alder reaction of di-2-azulenylacetylene with tetraphenylcyclopentadienone afforded 7,8,9,10-tetraphenyldiazuleno[2,1-a:1,2-c]naphthalene in one pot via autoxidation of the presumed 1,2-di-2-azulenylbenzene derivative. In contrast, a similar reaction of bis(1-methoxycarbonyl-2-azulenyl)acetylene with tetraphenylcyclopentadienone gave the 1,2-di-2-azulenylbenzene derivative. The following cyclodehydrogenation reaction of the benzene derivative with iron(III) chloride afforded diazuleno[2,1-a:1,2-c]naphthalene 6,11-bismethoxycarbonyl derivative. The redox behavior of these novel diazuleno[2,1-a:1,2-c]naphthalenes was examined by cyclic voltammetry (CV). These compounds exhibited two-step oxidation waves at +0.22 to +0.71 V upon CV, which revealed the formation of a radical cation and dication stabilized by the fused two azulene rings under the electrochemical oxidation conditions. Since the 1,2-di-2-azulenylbenzene derivative was oxidized at higher oxidation potentials (+0.83 and +1.86 V), the fusion of the two azulene rings to naphthalene increased electron-donating properties because of the formation of a closed-shell dicationic structure. Formation of the radical cation was characterized by UV-vis spectroscopy under the electrochemical oxidation conditions, although no evidence was obtained for the presumed dication under the conditions of the UV-vis spectroscopy measurement.     

Electronic coupling in tetraanisylarylenediamine mixed-valence systems: the interplay between bridge energy and geometric factors

We have investigated three organic mixed-valence systems that possess nearly identical inter-redox site distances and differ by the nature of the bridging units benzene, naphthalene, and anthracene: the N,N,N',N'-tetra(4-methoxyphenyl)-1,4-phenylenene-diamine radical cation (1+), the 1,4-bis(N,N-di(4-methoxyphenyl)-amino)naphthalene radical cation (2+), and the 9,10-bis(N,N-di(4-methoxyphenyl)amino)anthracene radical cation (3+). The electronic interactions in these systems have been studied by means of gas-phase ultraviolet photoelectron spectroscopy, vis/NIR spectroscopy, and electronic-structure calculations. The experimental and theoretical results concur to indicate that the strength of electronic interaction decreases in the following order of bridging units: benzene > naphthalene > anthracene. This finding contradicts the usual expectation that anthracene is superior to benzene as a driving force for electronic communication. We explain these results in terms of a super-exchange mechanism and its strong dependence on steric interactions.     

Azulene-Modified Polysiloxanes as Gas Chromatographic Stationary Phases: Comparison of the Separatory Properties of Azulene and Naphthalene

Azulene is an aromatic molecule with interesting properties, most notably a permanent dipole moment of 1.08D. This degree of polarity in the absence of heteroatoms is quite rare and offers potential for use in unique gas chromatographic stationary phases. Here, we report the first examples of azulene-derivatized stationary phases for gas chromatographic separations. Poly(dimethyl/azulenylmethyl) siloxane polymers containing 15 and 35% of an azulene derivative were synthesized, coated on capillary columns, and evaluated. To compare the effects of increased polarity vs. the effects of polarizability, isomeric naphthalene analogues were also prepared, coated, and evaluated. The coated phases displayed efficiencies up to 2700 plates/m. For both azulene and naphthalene columns, retention increased as substitution level increased. The more polarizable naphthalene columns tended to retain analytes more strongly. Columns were also evaluated for the separation of several different mixtures of isomers against a commercial HP-5 column. All azulene and naphthalene columns exhibited separations comparable to the commercial column. The solvation thermodynamic parameters phases were measured, showing an excellent linear relationship and no change in the mechanism of interaction over the temperature range measured.     

Nonempirical wave functions for very large molecules. I. The PRDDO/M method

We describe enhancements to the method of partial retention of diatomic differential overlap (PRDDO ). The new method, denoted PRDDO/M , employs a basis set of not quite orthogonal atomic orbitals (NQOAOS ) and utilizes sparse matrix techniques to greatly increase the computational efficiency for large molecules. Other modifications, including a complete reparametrization of the method against ab initio STO -3G calculations and implementation of integral screening/damping algorithms, are described. The method is an order of magnitude or more faster than are STO 3G single-point calculations using modern ab initio codes, with little loss in accuracy. © 1996 John Wiley & Sons, Inc.     

Photodissociation of azulene at 193 nm: ab initio and RRKM study

The ab initio/Rice-Ramsperger-Kassel-Marcus (RRKM) approach has been applied to investigate the photodissociation mechanism of azulene at 6.4 eV (the laser wavelength of 193 nm) upon absorption of one UV photon followed by internal conversion into the ground electronic state. Reaction pathways leading to various decomposition products have been mapped out at the G3(MP2,CC)//B3LYP level and then the RRKM and microcanonical variational transition state theories have been applied to compute rate constants for individual reaction steps. Relative product yields (branching ratios) for the dissociation products have been calculated using the steady-state approach. The results show that photoexcited azulene can readily isomerize to naphthalene and the major dissociation channel is elimination of an H-atom from naphthalene. The branching ratio of this channel decreases with an increase of the photon energy. Acetylene elimination is the second probable reaction channel and its branching ratio rises as the photon energy increases. The main C8H6 fragments at 193 nm are phenylacetylene and pentalene and the yield of the latter grows fast with the increasing excitation energy.     

An ab initio study of intermolecular hydrogen bonding between small peptide fragments

Several small peptide fragments are investigated with ab initio (Hartree-Fock) calculations, using Gaussian basis sets. Complexation energies, net atomic charges, and optimum geometries are obtained. The geometries predicted by the STO -6G, and 6–31G* basis sets are quite similar, whereas the binding energies obtaiend by the 6–31G calculations are higher than those obtained with STO -6G and 6–31G* basis sets.