A molecular orbital study of nitrogen inversion in aniline with extensive geometry optimization

The geometry and energy of aniline have been calculated using the 6-31G and 6-31G^*(5D) basis sets for the planar structure and various pyramidal structures, assuming that the ring and the N-atom bonded to it lie in the same plane, but otherwise with full geometry optimization. With the 6-31G basis set the planar structure is predicated to be the most stable, whereas the inclusion of polarization functions in the 6-31G^*(5D) basis set finds a pyramidal structure with the out-of-plane angle =42.3° to be most stable and the energy barrier to inversion via the planar transition state to be 1.59±0.02 kcal mol^–1, in close agreement with experiment. Completing the optimization, allowing the N-atom and the C- and H-atoms of the ring to take up equilibrium out-of-plane positions increases the calculated energy carrier to inversion by less than 0.1 kcal mol^–1 to 1.66 kcal mol^–1. The ring adopts a very shallow inverted boat-type conformation with N₇-C₁C₄ = 2.0°.     

Synthesis of heterocycles from molecular nitrogen as a nitrogen source

Nitrogen fixation is a very attractive process. We succeeded in nitrogen fixation using a TiCl₄‐ or Ti(O‐i‐Pr)₄‐Li‐TMSCl system. Nitrogen fixation proceeds at room temperature under 1 atmosphere pressure of nitrogen to give a mixture of titanium nitride complex 12 , titanium nitrogen complex 13 , and N(TMS)₄. Using the titanium nitrogen complexes 1 , various heterocycles were synthesized from the corresponding ketocarbonyl compounds. Nitrogen in air could be fixed using this method. The total syntheses of lycopodine and monomolin I were achieved from nitrogen in air as the nitrogen source. On the other hand, transmetalation of the nitrogen moiety of titanium nitrogen complexes 1 to a palladium complex was realized, and the non‐substituted anilines could be synthesized from ArX and N₂ in the presence of the palladium catalyst. Furthermore, amide could be synthesized from ArX, CO, and N₂ using the palladium catalyst.     

Emission from the afterglow of an ozonizer discharge through nitrogen

The afterglow produced from an ozonizer discharge of nitrogen showed a well developed second positive system and some emission bands from the first negative system in the virtual absence of other N₂ emissions. The NO_γ system was also observed but the NO_β system could not be detected. These observations are interpreted on the assumption that N₂ (A ³∑_u⁺) and vibrationally excited N₂ (X ¹∑_g⁺) are the principal energy carriers responsible for the excitation of the afterglow.     

UV spectral changes from rotational and inversion processes at the nitrogen center in aniline molecules

The decoupling of electrons by nuclear distortion and its influence on the UV spectrum are studied using CNDO/S calculations on aniline type molecules. Spectral changes with respect to the rotational angle of the amine group and the degree of hybridization at the nitrogen atom are investigated. The experimental spectrum is discussed on the basis of calculations performed for a variety of nuclear conformations. In particular, changes of the second (charge transfer) band are considered. INDO calculations of potential curves of aniline for the two degrees of freedom yield barriers of 1.2 kcal/ mole for the nitrogen inversion and of 7.5 kcal/mole for the internal amine rotation at the hybridization angle = 39.35°.     

Unimolecular dissociation of aniline molecular ion: A theoretical study

The potential energy surface (PES) for dissociation of aniline ion was determined using density functional theory molecular orbital calculations at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level. On the basis of the PES obtained, kinetic analysis was performed by Rice–Ramsperger–Kassel–Marcus (RRKM) calculations. The RRKM dissociation rate constants agreed well with previous experimental data. The most favorable channel was formation of the cyclopentadiene ion by loss of HNC, occurring through consecutive ring opening and re-closure to a five-membered ring. Loss of H could compete with the HNC loss at high energy, which occurred by direct cleavage of an N–H bond or through ring expansion.     

Emission spectrum of electron excited solid nitrogen

We report a new emission band in solid nitrogen between 1490 Å and 2320 Å, due to the de-excitation of the a′¹Σ^?_u molecular level and on the temperature dependence of some structures, in particular the ²D → ⁴S atomic nitrogen transition and the Vegard Kaplan bands.     

Two-dimensional molecular organization of pyridinecarboxylic acids adsorbed on graphite

Pyridinecarboxylic acids 3-9 are adsorbed from solution onto graphite to produce well-ordered adlayers that can be imaged by scanning tunneling microscopy. Hydrogen bonds involving the carboxyl groups and the nitrogen atom of the pyridyl ring play key roles in controlling the observed two-dimensional (2D) organization. Pyridinecarboxylic acids have a strong tendency to associate to form hydrogen-bonded chains and cyclic oligomers, which then pack to produce sheets. The preference for sheets ensures that molecular organization in 2D and 3D typically shows a significant degree of homology. Together, our observations highlight the potential of engineering similarly ordered 2D and 3D structures built from simple compounds that combine an inherent affinity for surfaces with an ability to engage in strong coplanar intermolecular interactions.     

Modelling the voltammetry of adsorbed enzymes and molecular catalysts

When redox enzymes are attached to electrodes and undergo direct electron transfer, their voltammetric responses exhibit diverse shapes that, if analysed correctly, may inform about various aspects of the catalytic mechanism. Here we review the models that have been proposed to interpret these signals in relation to the thermodynamics and kinetics of interfacial and intramolecular electron transfer and active site chemistry. We list the corresponding equations in forms that are ready to use for fitting, and the commands that run these fits in the open source software QSoas. We relate these models to those that have been used for characterizing small synthetic redox catalysts diffusing in solution.     

CVD synthesis of nitrogen doped carbon nanotubes using ferrocene/aniline mixtures

Nitrogen doped carbon nanotubes (N-CNTs) have been synthesized by the chemical vapour deposition (CVD) floating catalyst method using either 4-ferrocenylaniline or mixtures of varying concentrations of ferrocene/aniline together with toluene as added carbon source. The N-CNTs produced are less stable (thermal gravimetric analysis measurements), less graphitic and more disordered (transmission electron microscope measurements) than their undoped counterparts. The ratio of the Raman D- and G-band intensities increase with the nitrogen concentration used during the CNT growth. Furthermore, the transmission electron microscope (TEM) studies reveal that the CNTs are multi-walled (MW), and that the diameters of the N-MWCNTs can be controlled by systematically varying the concentrations of the nitrogen source. The TEM analysis also revealed that when ferrocenylaniline and ferrocene/aniline reactions are compared at similar Fe/N ratios, higher N doping levels are achieved (ca. 2-5×) when ferrocenylaniline is the catalyst.     

Thermal and FTIR spectroscopic analysis of the interactions of aniline adsorbed on to MCM-41 mesoporous material

The adsorption of aniline on Na-AlMCM-41 synthesized by us has been characterized by infrared spectroscopy, temperature programmed desorption (TPD), and differential thermal analysis methods. Aniline would be mostly bound to the mesostructure through weak pi interactions. On the mesostructure containing adsorbed water, the co-adsorption of aniline could occur by weak hydrogen bonding through surface water molecules. For water, two possible modes of adsorption have been identified. Different associations between aniline and hydrated and nonhydrated mesostructures have been evaluated in order to favor the posterior in situ polymerization of adsorbed aniline.     

Effect of substituting oxygen for terminal nitrogen in aniline oligomers: a DFT comparison of hydroxyl and amino terminated aniline trimers

Quantum mechanical density functional theory (DFT) calculations are reported for N,N'-bis(4'-hydroxyphenyl)-1,4-quinonediimine [henceforth referred to as the hydroxyl terminated trimer], a derivative of previously investigated aniline trimers. Calculations are also reported on all isomers, common oxidations states, and hydrochloride salts of this material. The significance of replacing terminal amino groups by hydroxyl groups is detailed. The hydroxyl terminated trimer has a calculated electron affinity larger than that of the corresponding amino terminated aniline trimer N,N'-bis(4'-aminophenyl)-1,4-quinonediimine. The electron affinity of the anti conformer of the hydroxyl terminated emeraldine base trimer is 0.059767 hartrees (37.5 kcal mol(-1)), whereas that of the amino terminated form is 0.052728 (33.1 kcal mol(-1)). The electron affinity of the anti conformer of the hydroxyl terminated emeraldine dihydrochloride salt trimer is 0.130546 hartrees (81.9 kcal mol(-1)), whereas that of the amino terminated dihydrochloride salt is only 0.118972 (74.7 kcal mol(-1)). Because previous work has suggested that a larger electron affinity in the salt form leads to improved effectiveness in the role of corrosion inhibitor, these high-level calculations suggest a new and superior material for this application.     

An unexpected reaction of 2-(cyclopent-2-enyl)aniline hydrochloride with dimethyldioxirane

An unusual direction of the reaction of 2-(cyclopent-2-enyl)aniline hydrochloride with dimethyldioxirane was found: the formation of two isomeric products,viz., 3- and 6-chloro-2-(cyclopent-2-enyl)anilines, was observed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1654–1655, August, 1998.     

On the heat capacity of adsorbed phases using molecular simulation

The heat capacities of argon, ammonia, and methanol on carbon black at 87.3, 240, and 300 K, respectively, have been investigated. The carbon black surface has been modeled with and without carbonyl groups. Part of this investigation is a decomposition of the heat capacity into its contributions from the different interaction potentials of an adsorption system. All systems show a spectrum of heat capacity versus loading, and this behavior depends on the carbonyl configuration present on the surface. For methanol and ammonia the variation of the heat capacity between the two for the same carbonyl configurations is greater than the variation in the heat of adsorption. Heat capacities of methanol and ammonia are generally dominated by fluid-fluid interactions due to the strong association of fluid particles through hydrogen bonding. The difference in the heat capacity behavior of the two fluids is an indicator of their different clustering behaviors on the carbon black surface. The presence of carbonyl groups reduces the fluid-fluid contributions to the heat capacity. This is due to the compensation of fluid-fluid interactions with fluid-functional group interactions. At 87.3 K a first layer transition to a solidlike state is present for argon and results in a large peak in the heat capacity on a bare surface. The presence of functional groups greatly reduces this peak in the heat capacity by disrupting the packing of argon on the surface and preventing a transition to a solidlike state.     

Molecular aniline clusters. II. The low-lying electronic excited states

The lowest electronically excited states of the aniline dimer and trimer related to the lowest π(?)←π transition of the monomer are investigated by applying time-dependent coupled cluster theory, primarily at the level of the (spin-component-scaled) CC2 model. Minimum energy structures in the vicinity of the Franck-Condon points were determined on the individual potential energy surfaces. For the dimer we find an excimer and a head-to-tail configuration (with the monomers substantially displaced relative to the ground state minimum) for the lowest (dark) and second lowest (bright) states, respectively. The excitation is delocalized on both chromophores for both of these states. For the trimer three distinct minima with quite different hydrogen-bonding arrangements are found for the three lowest states. In strong contrast to the dimer the excitation here is clearly localized on the individual aniline chromophores for each of these three states. One of the three geometries is rather similar to the ground state minimum, while the two others are rather different and thus have presumably quite small Franck-Condon factors. It can be expected that only the electronic origin of the first conformer can eventually be detected in the absorption spectrum of the trimer, provided that it is separated by high-enough barriers from other, energetically lower configurations.