Isomer stability of N6C6H6 cages

Recent theoretical studies have identified carbon-nitrogen cages that are potentially stable high energy density materials (HEDM). One such molecule is an N(6)C(6)H(6) cage in which a six-membered ring of nitrogen is bonded to C(3)H(3) triangles on both sides. This molecule is based on the structure of the most stable N(12) cage, with six carbon atoms substituted into the structure. In the current study, several N(6)C(6)H(6) isomers (including the previously studied cage) are examined by theoretical calculations to determine which is actually the most stable. Stability will be evaluated from two points of view: (1) thermodynamic stability of one isomer versus another and (2) kinetic stability of each isomer as determined by the energetics of bond breaking. Density functional theory (B3LYP), perturbation theory (MP2 and MP4), and coupled-cluster theory (CCSD(T)) are used in this study, along with the correlation-consistent basis sets of Dunning. Trends in thermodynamic and kinetic stability are discussed.     

Regioselective synthesis of 6-amino- and 6-amido-6-deoxypullulans

Hydrophobically modified polysaccharides that contain amine and amide groups possess valuable features for drug delivery and other applications. These chemical groups are known to play a fundamental role in the biological activity of important polysaccharides. Pullulan is known for its non-toxicity and biocompatibility, therefore, we have applied the versatile Staudinger reaction for the synthesis of regioselectively substituted pullulan derivatives containing amine or amide groups with promise for biomedical applications. The synthesis began with the regioselective bromination of pullulan at C-6 with N-bromosuccinimide and triphenylphosphine, providing 6-bromo-6-deoxy-pullulan, which is soluble in a range of organic solvents and therefore is a dynamic intermediate for the synthesis of other pullulan derivatives. Azide displacement of bromide from 6-bromo-6-deoxy-pullulan esters yielded the corresponding 6-azido-6-deoxy-pullulan esters. Staudinger reduction of these azides efficiently and chemoselectively afforded the corresponding amino- or amidopullulans.     

6, 6-Dialkyl- und 6, 6-Polymethylen-fulvene

The electronic, infrared and NMR spectra of 6, 6-dialkyl-fulvenes and of 6, 6-poly-methylene-fulvenes are reported.     

金属原子（离子）-苯配合物的电子转移反应

用密度泛函理论（ＤＦＴ／ＢＬＹＰ）在６－３１Ｇ基组水平上研究了金属原子－苯与离子－苯配合物的气相电子转移过程,得到了Ｍ（Ｌｉ,Ｎａ,Ｍｇ）－Ｃ６Ｈ６和Ｍ＾＋－Ｃ６Ｈ６络合物以及它们之间电子转移过程的先驱络合物的最优几何构型和电子结构。同时,利用线性坐标确定了过滤态的结构,结果表明：ＤＦＴ方法计算得到的单体,即原子（离子）－苯的构型,同ＭＰ２结果较为一致。先驱络合物具有Ｃ６ν对称性,给体与受体间距离     

6A6B, 6A6C,and 6A6D-ditosylates of β-cyclodextrin

Regio-isomers, 6A6B, 6A6C, and 6A6D-ditosylates of β-cyclodextrin prepared by the reaction of β-cyclodextrin with tosyl chloride were easily and effectively separated through reversed phase column chromatography and assigned.     

The tautomerism of 6-hydroxy-, 6-amino- and 6-acylamino-7-azaindolines

The lactam-lactim tautomerism of 6-hydroxy-7-azaindolines and amino-imine tautomerism of 6-amino- and 6-acylamino-7-azaindolines has been studied by IR and UV spectroscopy. It is shown that the lactam-lactim tautomeric equilibrium of 6-hydroxy-7-azaindolines in contrast to the other analogous N-heteroaromatic compounds is not completely shifted for the lactam. The commensurable amounts of both tautomeric forms can be observed in the solutions of 6-hydroxy-7-azaindolines and it is possible to elucidate the influence of the solvent polarity upon the lactam-lactim tautomeric equilibrium. The tautomeric equilibrium of 6-amino- and 6-acylamino-7-azaindolines is practically completely shifted for the amino form, and even acylation with p-toluene-sulfonic acid does not result in a noticeable shift of the tautomeric equilibrium for the amino form in contrast to the other N-heterocyclic amines.     

Preparation of 6-chloro-6-desoxy- and 6-iodo-6-desoxycellulose

Conclusions The reaction of 2,3-di-O-acetylcellulose with N-chloro- or N-iodosuccinimide and triphenylphosphine gave the 6-chloro-6-desoxy- and 6-iodo-6-desoxycellulose acetates with a respective degree of substitution (DS) in halogen of 0.8–1.0 and 0.7. The deacetylation of these compounds gave 6-chloro-6-desoxycellulose (DS 0.8) and 6-iodo-6-desoxycellulose (DS 0.6).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2158–2160, September, 1977.     

Application of algebraic method to the high overtones of C6H6 and C6D6

Both the spectra and infrared transition strengths of C₆H₆ and C₆D₆ for the C? H stretching overtones up to as high as v = 10 are described in high precision with few parameters (six for the spectra and four for the transition strengths) by the Iachello–Oss algebraic model. The Hamiltonian model is solved in the symmetry adapted bases, which are constructed by the symmetrized boson representation (SBR) technique. The results show that the combination of the algebraic method and SBR technique is a powerful method for describing vibrations of large molecules and high overtones. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Electron attachment to MoF6, ReF6, and WF6; reaction of MoF6(-) with ReF6 and reaction of Ar+ with MoF6

Rate constants were measured for electron attachment to MoF(6), ReF(6), and WF(6) in 133 Pa of helium gas using a flowing-afterglow Langmuir-probe apparatus. The experiment is a thorny one because the molecules tend to form oxide impurities on feedline surfaces and because of thermal decomposition of MoF(6) on surfaces as the gas temperature is increased. The electron attachment rate constant for MoF(6) is (2.3+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only MoF(6) (-) is formed in the temperature range of 297-385 K. The rate constant increases with temperature up to the point where decomposition becomes apparent. Electron attachment to ReF(6) occurs with a rate constant of (2.4+/-0.8)x10(-9) cm(3) s(-1) at 297 K; only ReF(6) (-) is produced. MoF(6) (-) reacts with ReF(6) to form ReF(6) (-) on essentially every collision, showing definitively that the electron affinity of ReF(6) is greater than that of MoF(6). A rate constant of (5.0+/-1.3)x10(-10) cm(3) s(-1) was measured for this ion-molecule reaction at 304 K. The reverse reaction is not observed. The reaction of Ar(+) with MoF(6) was found to produce MoF(5) (+)+F, with a rate constant of (1.8+/-0.5)x10(-9) cm(3) s(-1). WF(6) attaches electrons so slowly at room temperature that the attachment rate was below detection level (< or =10(-12) cm(3) s(-1)). By 552 K, the attachment rate constant reaches a value of (2+/-1)x10(-10) cm(3) s(-1).     

Jahn-Teller effect in van der Waals complexes; Ar-C6H6 + and Ar-C6D6 +

The two asymptotically degenerate potential energy surfaces of argon interacting with the X (2)E(1g) ground state benzene(+) cation were calculated ab initio from the interaction energy of the neutral Ar-benzene complex given by Koch et al. [J. Chem. Phys. 111, 198 (1999)] and the difference of the geometry-dependent ionization energies of the complex and the benzene monomer computed by the outer valence Green's function method. Coinciding minima in the two potential surfaces of the ionic complex occur for Ar on the C(6v) symmetry axis of benzene(+) (the z axis) at z(e)=3.506 A. The binding energy D(e) of 520 cm(-1) is only 34% larger than the value for the neutral Ar-benzene complex. The higher one of the two surfaces is similar in shape to the neutral Ar-benzene potential, the lower potential is much flatter in the (x,y) bend direction. Nonadiabatic (Jahn-Teller) coupling was taken into account by transformation of the two adiabatic potentials to a two-by-two matrix of diabatic potentials. This transformation is based on the assumption that the adiabatic states of the Ar-benzene(+) complex geometrically follow the Ar atom. Ab initio calculations of the nonadiabatic coupling matrix element between the adiabatic states with the two-state-averaged CAS-SCF(5,6) method confirmed the validity of this assumption. The bound vibronic states of both Ar-C(6)H(6) (+) and Ar-C(6)D(6) (+) were computed with this two-state diabatic model in a basis of three-dimensional harmonic oscillator functions for the van der Waals modes. The binding energy D(0)=480 cm(-1) of the perdeuterated complex agrees well with the experimental upper bound of 485 cm(-1). The ground and excited vibronic levels and wave functions were used, with a simple model dipole function, to generate a theoretical far-infrared spectrum. Strong absorption lines were found at 10.1 cm(-1) (bend) and 47.9 cm(-1) (stretch) that agree well with measurements. The unusually low bend frequency is related to the flatness of the lower adiabatic potential in the (x,y) direction. The van der Waals bend mode of e(1) symmetry is quadratically Jahn-Teller active and shows a large splitting, with vibronic levels of A(1), E(2), and A(2) symmetry at 1.3, 10.1, and 50.2 cm(-1). The level at 1.3 cm(-1) leads to a strong absorption line as well, which could not be measured because it is too close to the monomer line. The level at 50.2 cm(-1) gives rise to weaker absorption. Several other weak lines in the frequency range of 10 to 60 cm(-1) were found.     

Substituent effects in C6F6-C6H5X stacking interactions

Parallel displaced and sandwich configurations of hexafluorobenzene-substituted benzene dimers are studied by ab initio molecular orbital methods up to the MP2(full)/aug-cc-pVDZ level of theory to reveal how substituents influence pi-pi interactions. Two minimum energy configurations are found, one with the substituent group away from the pi-face of the hexafluorobenzene ring (2a-f) and the other with the substituent group on top of the pi-face of the hexafluorobenzene (3a-f). Higher binding energies are predicted for dimers with the substituent on the pi-face (3a-f). All sandwich dimers (4a-e) are found to be saddle points on the potential energy surfaces. A parallel-displaced minimum energy configuration is also predicted for the parent complex, C6F6-C6H6, which is in contrast to predictions based on quadrupole moments of benzene and hexafuorobenzene. The preference for the parallel displaced, rather than the sandwich configuration, is rationalized based on the smaller interplanar distance in the former. The closeness of contact in the parallel-displaced dimers leads to greater binding energies. The shape of the electron density isosurface of the monomers is suggested to provide a guide for the prediction of how arenes stack with one another. A large difference in binding energy between the C6F6 complex of aniline (3e) and N,N-dimethylaniline (3f) is calculated, and charge-transfer interactions are suggested to play a role in the latter.     

One-pot syntheses of 6-mercaptopurines (6MP) from 4,5-diamino-6-chloro-pyrimidines

A one-pot synthesis of 6-mercaptopurines from 4,5-diamino-6-chloro-pyrimidine, an aldehyde and elemental sulfur is presented. The key advantage of this procedure is that it utilizes the in situ generated H₂S to convert the chloro to a mercapto group.     

C60NH5/6, 6/6异构体的理论研究

用半经验的AM1, PM3及ab initio方法对C60NH两种异构体的结构及光谱进行了理论计算。结果表明, 具有开环结构的C60NH的5/6异构体稳定性要高于具有闭环结构的6/6异构体。计算了两种异构体开环与闭环过程的反应坐标, 发现6/6开环异构体是势能面上的一局部最小点, 而5/6闭环异构体不存在6/6异构体的H可以在两种镜面异构体之间快速翻转, 使其核磁共振谱呈现C2v对称性。通过振动分析确认了所优化的构型确实为势能面的能量最低点, 并得到了C60NH各异构体的红外光谱。     

Ordnungszustände im system polyamid-6 und polyamid-6, 6

Blends of PA-6 and PA-6,6 were studied by DSC for different conditions of crystallization. All samples were characterized by x-ray diffraction. From dilute solution the components crystallize in separate modifications. In the melt both components are compatible. PA-6- and PA-6,6-segments are linked together. During rapid quenching of the melt in the samples of about equal composition of PA-6 and PA-6,6 a modification is formed possibly built by a three-dimensional network of hydrogen bonds between PA-6- and PA-6,6-segments. If the samples of the same composition are annealed at 25 K below the melting temperatures of PA-6 and PA-6,6 for 3 hours in each case a modification appears as in quenched samples in addition to only partially ordered crystallites of PA-6 and PA-6,6. Despite optimal annealing there is no complete separation of the components.     

Efficient conversion of 6-cyanopurines into 6-alkoxyformimidoylpurines

An extremely simple method for the selective synthesis of 9-aryl and 9-alkyl 6-alkoxy or 6-alkoxyformimidoylpurines from the corresponding 6-cyanopurines is described. The reaction is carried out with methanol or ethanol in the presence of DBU. At room temperature, nucleophilic attack by the primary alcohol occurs selectively on the cyano carbon atom, leading to 6-alkoxyformimidoylpurines in good yields. Heating the reaction mixture at a temperature greater than or equal to 78 degrees C leads to nucleophilic substitution of the substituent in the 6-position by the alkoxy group, generating the corresponding 6-alkoxypurines, also in excellent yields. The 6-alkoxyformimidoylpurines were used as intermediates in the synthesis of 6-carboxamidinopurines by reaction with methylamine (for 9-methylpurine 5a) or methyl ammonium chloride (for 9-arylpurines and 5b and 5c).     

Towards hydroxylated nylon 6: oligomers from a protected 6-amino-6-deoxy- -allonate

The first synthesis of linear oligomers (a dimer, tetramer, hexamer and octamer) of fully hydroxylated analogues of nylon 6 by iterative formation of peptide bonds from a protected 6-amino-6-deoxy- -allonate monomer is reported.     

Experimental and theoretical evidence for U(C6H6) and Th(C6H6) complexes

The vibrational spectra of UBz and ThBz have been measured in solid argon. Complementary quantum chemical calculations have allowed the assignments of the vibrational spectra. According to the calculations, AcBz are stable molecules, as well as other species like BzAcBz and BzAc2Bz. Experimentally, there is no evidence for the sandwich compounds BzAcBz and BzAc2Bz due to the limitations in the reagent concentrations.     

In search of benzene-like Sn6(6-): synthesis of Na4CaSn6 with interconnected cyclohexane-like Sn6(6-)

The title compound was synthesized in an attempt to produce stacked benzene-like Sn6(6-) rings separated by alkaline-earth cations in analogy with the recently reported stacks of aromatic cyclopentadienyl-like Sn5(6-) in Na8BaSn6 (in addition to isolated Sn4- anions). The resulting compound, synthesized from a stoichiometric mixture of the elements at high temperature, has the "correct" stoichiometry with six tin atoms and six positive charges. However, the rings of Sn6(6-) are puckered into chair-type cyclohexanes that are interconnected into isolated cylindrical tubes stuffed with Ca2+ between the rings. Such tubes, if fused to each other, form the hexagonal diamond structure. The new compound is electronically balanced according to magnetic and four-probe resistivity measurements. Reported are also the synthesis and properties of Na10EuSn12 and Na10YbSn12 which are isostructural with the known Na10CaSn12.