DFT-PCM Study of the Bond Dissociation Energies of N-nitrosoindole Compounds in Acetonitrile

Quantum chemical calculations are used to estimate the equilibrium N–NO bond dissociation energies (BDEs) in acetonitrile (MeCN) for seven N-nitrosoindole compounds. These compounds are studied by employing the hybrid density functional theory (B3LYP, B3P86 and B3PW91) methods together with 6-31G^∗∗ basis sets. The obtained results are compared with the available experimental results. It is demonstrated that the B3PW91 method is the best of these methods to compute the bond dissociation energies of N-nitrosoindole compounds. The solvent effects on the BDEs of the N–NO bond are analyzed and it is shown that the N–NO BDEs in a vacuum, computed by the B3LYP method, are the closest to the computed values in MeCN and the average solvent effect is 4.0 kJ⋅mol⁻¹. The substituent effects on the N–NO BDEs were further analyzed and it is found that the N–NO BDE increases with increments of the Hammett constants of substituent groups on the benzene ring for N-nitrosoindole compounds, except the compound with 5-NO₂−C₈H₅N–NO. Finally, N-nitrosoindole compounds and the other NO-donors (N-nitroso compounds) are compared.     

Computational investigation on 2,6-diamino-3,5-dinitropyridine-1-oxide crystal

Density functional theory calculations were performed on crystalline 2,6-diamino-3,5-dinitropyridine-1-oxide (ANPyO). The conduct bands are generally quite flat, while the valence bands are uneven. The carbon, oxygen and amino nitrogen atoms make up the narrow lower energy levels. While the carbon, amino nitrogen and atoms in nitro group make up the higher energy levels. Change of electronic charges for the decrease of the cell edge a and c are almost the same, but different from the decrease of the cell edge b, indicating an anisotropic effect related to compressions. The C-Nitro and the N–O (N-oxide) bonds are the weakest, and tend to rupture upon external stimulation. The Mulliken population for the N–O (N-oxide) bond in crystal is much smaller than that in molecule, indicating that the molecular packing weakens this bond. Judged by the fact of N–O (N-oxide) bond being weaker than C-Nitro bond, ANPyO is sensitive to mechanic impact than 1,3,5-triamino-2,4,6-trinitrobenzene, which is in good agreement with experiment. The crystal lattice energy is predicted to be −166.03 kJ/mol, after being corrected for basis set superposition error.     

Molecular Structure and Conformational Composition of 1-[(Methylthio)methyl]-2-nitrobenzene (MTMNB): A Theoretical and Experimental Study

The conformational composition of gaseous MTMNB and the molecular structures of the rotational forms have been studied by electron diffraction at 130^∘C aided by results from ab initio and density functional theory calculations. The conformational potential energy surface has been investigated by using the B3LYP/6-31G(d,p) method. As a result, six minimum-energy conformers have been identified. Geometries of all conformers were optimized using MP2/6-31G(d,p), B3LYP/6-31G(d,p), and B3LYP/cc-pVTZ methods. These calculations resulted in accurate geometries, relative energies, and harmonic vibrational frequencies for all conformers. The B3LYP/cc-pVTZ energies were then used to calculate the Boltzmann distribution of conformers. The best fit of the electron diffraction data to calculated values was obtained for the six conformer model, in agreement with the theoretical predictions. Average parameter values (r_a in angstroms, angle α in degrees, and estimated total errors given in parentheses) weighted for the mixture of six conformers are r(C–C) = 1.507(5), r(C–C)_{ring, av} = 1.397(3), r(C–S)_av = 1.814(4), r(C–N) = 1.495(4), r(N–O)_av = 1.223(3), ∠(C–C–C)_ring = 116.0–122.5, ∠ C6–C4–C7 = 118.2(4), ∠ C–C–S = 113.6(6), ∠ C–S–C = 98.5(12), ∠ N–C–C4 = 121.9(3), ∠(O–N–C)_av = 116.8(3), ∠ O–N–O = 127.0(4). Torsional angles could not be refined. Theoretical B3LYP/cc-pVTZ torsional angles for the rotation about C–N bond, φ_C−N, were found to be 30.5–36.5^∘ for different conformers. As to internal rotation about C–C and C–S bonds, values of φ_C−C = 68–118^∘ and φ_C−S = 66–71^∘ were obtained for the three most stable conformers with gauche orientation with respect to these bonds. Some conclusions of this work were presented in a short communication in Russ. J. Phys. Chem. 2005, 79, 1701.     

Aromaticity in heterocycles: new HOMA index parametrization

Abstract  

A new parametrization for the Harmonic Oscillator Model of Aromaticity (HOMA) index to determine aromaticity of heterocycles is introduced. The new HOMA for Heterocycle Electron Delocalization (HOMHED) is based on the experimental data from electron diffraction X-ray for the reference molecules used to estimate the simple, double, and optimal bond lengths. Bond length of “pure” single and double bonds of non-conjugated systems or systems without π-electrons and/or n-electron delocalization were considered. The HOMHED index was determined for a series of five and six heterocycles with C–C, C–N, C–O, C–S, N–N, N–O, and N–S bonds. The π-electron delocalization of these heterocycles was determined by Krygowski-reformulated HOMA and HOMHED and it was proved that HOMHED worked in line with HOMA for all heterocycles, except those containing oxygen, which were found to be weak aromatic from Krygowski rHOMA calculations.     

Supramolecular amide and thioamide synthons in hydrogen bonding patterns of N-aryl-furamides and N-aryl-thiofuramides

The supramolecular synthon of amide group in the primary and secondary amides is well recognized to be infinite chains of the C(4) type formed by the intermolecular hydrogen bond of the type N–HO=C. On the other hand, there is a lack of structural data for the thioamides. Three compounds belonging to the class of N-aryl-fura-mides (N-(4-bromophenyl)-5-bromo-2-furancarboxamide, N-(4-chlorophenyl)-5-bromo-2-furancarboxamide) and to the class of N-aryl-thiofuramide (N-(4-methoxyphenyl)-2-furanthiocarboxamide) are prepared and characterized by the NMR spectroscopy in solution; molecular and crystal structures in the solid state have been determined by X-ray single crystal diffractometry and the structures in the gas phase by DFT and AM1 calculations. The investigation is carried out in order to establish supramolecular amide and thioamide synthons of hydrogen bonding patterns in these crystal structures. The geometry of the N–HO=C and the N–HS=C type of hydrogen bonds are compared due to the possibility of the N–H amide group to form intramolecular hydrogen bond with the furan oxygen atom, thus, commonly, leading to the three-center hydrogen bond pattern. The competition between the S=C proton acceptor of thioamides and the other proton acceptors (such as methoxy group) for the amide N–H proton donor group has been investigated. In that context, the above-mentioned compounds are correlated with the others of this class, structurally determined, so far.     

A Theoretical Study of Amine Bonding in Titanium Alkoxide Adducts

Summary. DFT calculations were carried out on Ti₂(OCH₃)₈ (NH₂CH₃)₂ and Ti₂(OCH₃)₈(NH₃)₂, which are model compounds for the previously isolated amine adducts Ti₂(OR)₈(NH₂ R′)₂. The calculations show that the Ti–N bond strength is weak; however, coordination of the amine to the metal center is supported by a N–H···O hydrogen bond of the amine with the neighboring alkoxo ligand. The Ti–N interaction is purely σ in nature, while the Ti–O interactions include both σ and π contributions. The lowest unoccupied molecular orbitals are mainly localized on Ti t_2g-like orbitals.     

Sulfenylation reactions activated by thionyl and sulfuryl chlorides

Reactions ofN-(4-nitrophenylthio)morpholine,N,N′-thiobismorpholine, andN,N′-dithiobismorpholine with thionyl chloride or sulfuryl chloride at −40°C afford electrophilic chlorosulfenylating reagents, which add to the C=C bond of norbornene in high yields. Semiempirical quantum-chemical calculations and comparison of the relative reactivity of the sulfenylating complexes formed upon activation of arenesulfenamides by sulfur and phosphorus oxohalides were performed. The mechanism of the reactions is discussed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2516–2518, December, 1998.     

Multinuclear NMR investigation on organometallic gold(III) pentafluorophenylarylazoimidazole complexes

Reaction of [Au(C₆F₅)(tht)₂Cl](OTf) with RaaiR′ in CH₂Cl₂ medium leads to [Au(C₆F₅)(RaaiR′)Cl](OTf) [RaaiR′ = p-R–C₆H₄–N=N–C₃H₂–NN-1-R′, (1–3), abbreviated as N,N′-chelator, where N(imidazole) and N(azo) represent N and N′, respectively; R = H (a), Me (b), Cl (c) and R′ = Me (1), CH₂CH₃ (2), CH₂Ph (3), tht is tetrahydrothiophen]. The maximum molecular peak of [Au(C₆F₅)(MeaaiMe)Cl] is observed at m/z 599.51 (100 %) in the FAB mass spectrum. Ir spectra of the complexes show –C=N– and –N=N– stretching near at 1590 and 1370 cm⁻¹ and near at 1510, 955, 800 cm⁻¹ due to the presence of pentafluorophenyl ring. The ¹H-NMR spectral measurements suggest methylene, –CH₂–, in RaaiEt gives a complex AB type multiplet while in RaaiCH₂Ph shows AB type quartets. ¹³C-NMR spectrum of complexes confirm the molecular skeleton. In the ¹H-¹H-COSY spectrum as well as contour peaks in the ¹H-¹³C HMQC spectrum for the present complexes, assign the solution structure and stereoretentive conformation. The electrochemistry gives the ligand reduction peaks.     

DFT studies and AIM analysis of intramolecular N–H···O hydrogen bonds in 3-aminomethylene-2 methoxy-5,6-dimethyl-2-oxo-2,3-dihydro-2λ5-[1,2]oxaphosphinin-4-one and its derivatives

The intramolecular N–H···O hydrogen bonds in 3-aminomethylene-2 methoxy-5,6-dimethyl-2-oxo-2,3-dihydro-2λ⁵-[1,2]oxaphosphinin-4-one and its derivatives (F, H, Li, -BeH) were studied by DFT (density functional theory) methods. The results of calculations were obtained at B3LYP/6-311++G(d,p) level on model species, with the resonance-assisted hydrogen bonds (RAHB). Topological parameters such an electron density, its Laplacian, kinetic electron energy density, potential electron energy density, and total electron energy density at the bond critical points (BCP) of H···O/N–H contact bonds from Bader’s ‘Atoms in molecules’ (AIM) theory were analyzed in details. The energy of the N–H···O interactions studied here was found rather weak (E _HB = 2.53–12.08 kcal/mol). The results of AIM ellipticity indicated π-delocalization over all six atoms within ring.     

Conformational properties of <Emphasis Type="Italic">ortho</Emphasis>-nitrobenzenesulfonamide in gas and crystalline phases. Intra- and intermolecular hydrogen bond

A combined gas-phase electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pvtz, MP2/cc-pvtz) study of molecular structure of 2-nitrobenzenesulfonamide (2-NBSA) was carried out. Quantum chemical calculations showed that 2-NBSA has four conformers, two of which are stabilized by intramolecular hydrogen bond. The latter (with the S–N bond in a close to orthogonal position around the phenyl ring and differing from each other by staggered or eclipsed positions of the N–H and S=O bonds in the SO₂NH₂ group) presented in a saturated vapor over 2-NBSA at T = 433 (3) K in commensurable amounts. Experimental internuclear distances (Ǻ) for the staggered conformer are (?): r _h1(C–H)_av. = 1.071(9), r _h1(C–C)_av. = 1.390(4), r _h1(C–S) = 1.789(8), r _h1(S=O)_av. = 1.427(6), r _h1(S–N) = 1.644(6), r _h1(N–O)_av. = 1.221(4), r _h1(C′–N) = 1.487(8), r _h1(N–H)_av. = 1.014. Calculations at B3LYP/cc-pvtz level were performed to determine the structure and the energies of the transition states between conformers. It was shown that the conformer structures of free molecule differ from those of a molecule stabilized by intermolecular hydrogen bonds in a crystal. Influence of a substituent X (X = –CH₃, –NO₂) on conformational features of the ortho-substituted benzenesulfonamide was established.     

Adsorption of 2,4,6-trinitrotoluene on Al(111) ultrathin film: periodic DFT calculations

The adsorption of 2,4,6-trinitrotoluene (TNT) molecule on the Al(111) ultrathin film were investigated by the generalized gradient approximation (GGA) of density functional theory (DFT). The calculations employ a supercell (4 × 4 × 2) model and three-dimensional periodic boundary conditions. The strong attractive forces between oxygen and aluminum atoms induce the N–O bond breaking of the TNT. Subsequently, the dissociated oxygen atoms and radical fragment of TNT oxidize the Al ultrathin film. The N–O bond of the o-NO₂ group is easier to rupture than that of the p-NO₂ group after the adsorption of the TNT molecule on the Al(111). Except for the breaking of the N–O bonds of the nitro group, other bonds of TNT molecule do not dissociate. The largest adsorption energy is −747.3 kJ/mol. The most of charge transfer is 3.42 e from the Al(111) to the fragment of TNT molecule. The aluminum ultrathin film is readily oxidized by the radical fragment of TNT, which is initiated by the dissociated O atoms from the nitro group.     

Local dipole interactions induce helicity of (<Emphasis Type="Italic">S</Emphasis>)-2-butyl-<Emphasis Type="Italic">N</Emphasis>-(1,8-naphthaloyl)-2-aminobenzoate molecules containing 1,8-naphthalimide rings utilized as a column building blocks: X-ray and quantum mechanical studies

In the crystal of triclinic symmetry the title compound contains four independent molecules, which differ in the conformation of the aliphatic carbon chain (T, G ⁺and G ⁻) and in the helicity (M or P) of the N-(1,8-naphthaloyl)-2-aminobenzoate (NAB) unit. Quantum chemical MP2 calculations showed that isolated molecules favor helicity of NAB bichromophores most likely due to attractive interactions between local dipoles formed along carbonyl bonds, such that the helical arrangement of O=C–C–C–N–C=O fragments is stabilized by intramolecular interactions between terminal anti-parallel local carbonyl dipoles. In the crystal structure, columnar stacking of the anti-parallel 1,8-naphalimide rings is observed. In a column the neighboring NAB units display opposite helicity.     

Palladium(II) Pyridinecarboxaldimine Complexes Derived from Unsaturated Amines

Pyridinecarboxaldimines (N–N′) derived from pyridin-2-ylcarboxaldehydes and unsaturated amines add to [PdCl₂(coe)]₂ (coe = cis-cyclooctene) to give complexes of the type PdCl₂(N–N′) in moderate yields. The palladium complexes have been investigated as substrates for hydroboration reactions and as antifungal agents against Aspergillus niger, A. flavus, Candida albicans, and Saccharomyces cerevisiae.     

Analytical approximation of the conformational dependence of the exchange interaction parameters for axially coordinated Cu(II) complexes with nitroxides

Analytical expressions relating the exchange parameters to the geometrical characteristics that determine the position of the radical fragment >N−O in axially coordinated Cu(II) complexes are derived from the results of quantum chemical calculations. The contributions of the delocalization (major) and direct (minor) mechanisms are considered. The expressions are tested by application to some complexes with known geometrical structures. Institute of Chemical Kinetics and Combustion, Russian Academy of Sciences, Siberian Branch, Novosibirsk. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 1, pp. 27–33, January–February, 1995. Translated by I. Izvekova     

Effect of molecular and crystal structure ofN-naphthylurethanes (carbamates) on their IR spectra

A comparative analysis of the IR spectra in the region of 3000–400 cm⁻¹ of four urethanes (methyl-(N-(1-naphthyl) carbamate, ethyl-N-(1-naphthyl) carbamate, dimethyl-N,N′-(1,5-naphthylene) dicarbamate, and diethyl-N,N′-(1,5-naphthylene) dicarbamate) with known molecular and crystal structures was carried out. The assignment of the bands related to the vibrations of the urethane and naphthyl fragments was refined on the basis of the study of the crystalline samples, melts, solutions, and deuterated analogs. The effect of the degree of conjugation of the urethane group with the naphthalene ring on the Amide II vibration frequency in the crystals was shown. It was suggested that the stretching vibrations of the C(Ar)−N bond in naphthylurethanes (unlike aliphatic derivatives) make a considerable contribution to the Amide II vibration, while the planar deformation vibration of the N−H bond was proved to be more significant for Amide III than for Amide II. In addition, strong nonspecific intermolecular interactions in the crystal can weaken valent bonds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 300–303, February, 1998.     

The potential energy surface of the triazadiphosphole formation

The formal GaCl₃-assisted [3+2] cycloaddition of two (Me₃Si)₂N–N(SiMe₃)–PCl₂ molecules resulting in the formation of a triazadiphosphole has been studied by means of B3LYP/6-31G(d,p) computations. These calculations revealed a stepwise reaction mechanism starting from the disguised 1,3-dipole and dipolarophile (Me₃Si)₂N–N(SiMe₃)–PCl₂. Comparison of the potential energy surface for the formation of a triazadiphosphole in the presence and without a Lewis acid indicate, that addition of a Lewis acid such as GaCl₃ decreases the activation barriers to Me₃Si–Cl elimination, in accord with experiment. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">N′,N′</Emphasis>-dialkylhydrazides and their protonated forms: <Emphasis Type="Italic">ab initio</Emphasis> calculations and studies by physical methods

RHF/6-31G(d) and MP2/6-31G(d) quantum-chemical calculations of N′,N′-dimethylethanohydrazide molecule and also MP2/6-31G(d) calculations of its protonated forms were performed. With the use of IR and ¹H NMR spectroscopy the series of N′,N′-dialkylhydrazides and their salts with HCl and H₂SO₄ were studied. The position of proton addition was determined. The experimental results were compared with the calculated findings.     

Crystal Structure and Conformation of a 10-Thiabilirubin

 A crystal structure determination of a bilirubin analog with a sulfur instead of a C(10)–CH₂ linking the two dipyrrinones is reported. Conformation-determining torsion angles and key hydrogen bond distances and angles are compared to those obtained from molecular dynamics calculations as well as to the corresponding data from X-ray determinations and molecular dynamics calculations of bilirubin. Like other bilirubins, the component dipyrrinones of the analog are present in the bis-lactam form with (Z)-configurated double bonds at C(4) and C(15). Despite the large differences in bond lengths and angles at –S–vs.–CH₂–, the crystal structure shows considerable similarity to bilirubin: both pigments adopt a folded, intramolecularly hydrogen-bonded ridge-tile conformation stabilized by six hydrogen bonds – although the interplanar angle of the ridge-tile conformation of the title compound is smaller (∼ 86°) than that of bilirubin (∼ 98°). The collective data indicate that even with long C–S bond lengths and a smaller C–S–C bond angle at the pivot point on the ridge-tile seam, intramolecular hydrogen bonding persists.     

Selective synthesis of 1,3-dialkyl-4-nitro-1,2,3-triazolium salts from 1-alkyl-4-nitro-1,2,3-triazoles and dialkyl sulfates

The process of alkylation of 1-alkyl-substituted 4-nitro-1,2,3-triazoles with dimethyl and diethyl sulfates has been studied. The structures of the N,N’-dialkyl-C-nitro-1,2,3-triazolium alkylsulfates and perchlorates has been confirmed by IR, ¹H and ¹³C NMR spectroscopy. Alkylation with an excess of dialkyl sulfate occurred regioselectively at N-3 with the formation of 1,3-dialkyl-4-nitro-1,2,3-triazolium salts, which is in agreement quantum-chemical calculations of the relative stability of the corresponding isomeric cations. The molecular and crystal structures of the first example of this type of salt – 1,3-diethyl-4-nitro-1,2,3-triazolium perchlorate – have been determined by X-ray crystallo-graphy. Nitrotriazolium salts with mixed alkyl substituents – 3-ethyl-1-methyl- and 1-ethyl-3-methyl-4-nitro-1,2,3-triazolium salts – have been synthesized an studied for the first time.     

Synthesis and structure of the product of bis-condensation of 4-methyl-2,6-diformylphenol with dimethyl N′,N′-hydrazine diacetate

Bis-condensation of 4-methyl-2,6-diformylphenol with dimethyl N′,N′-hydrazine diacetate gave product I. The structure of I was determined by X-ray analysis. The conformations of the two side chains of dimethyl N′,N′-hydrazine diacetate are significantly different. The position of one chain is fixed by the intramolecular H-bond of O−H.…N type. Due to its conformation, compound I is partly ready for complex formation with d-metals. Institute of Applied Physics, Academy of Sciences, Moldova Republic. Institute of Chemistry, Academy of Sciences, Moldova Republic. Translated fromZhurnal Struktumoi Khimii, Vol. 35, No. 3, pp. 91–98, May–June, 1994. Translated by L. Smolina