Density functional study on the reaction mechanism of proton transfer in 2-pyridone: effect of hydration and self-association

The proton-transfer mechanism in the isolated, mono, dehydrated forms and dimers of 2-pyridone and the effect of hydration or self-assistance on the transition state structures corresponding to proton transfer from the keto form to the enol form have been investigated using B3LYP and BH-LYP hybrid density functional methods at the 6-311++G (2d, 2p) basis set level. The barrier heights for both H2O-assisted and self-assisted reactions are significantly lower than that of the bare tautomerization reaction from 2-pyridone to 2-hydroxypyridine, implying the importance of the superior catalytic effect of H2O and (H2O)2 and the important role of 2-pyridone itself for the intramolecular proton transfer. Long-range solvent effects have also been taken into account by using the continuum model (Onsager model and polarizable continuum model (PCM)) of water. The tautomerization energies and the potential energy barriers are increased both for the water-assisted and for the self-assisted reaction because of the bulk solvent, which imply that the tautomerization of PY becomes less favorable in the polar solvent.     

Structure and vibrational frequencies of 2-butanimine

The conformational behavior and structural stability of 2-butanimine were investigated by utilizing ab initio calculations with 6-311++G** basis set at HF, MP2, B3LYP and BLYP levels. The vibrational frequencies of 2-butanimine were computed. Complete vibrational assignments were made on the basis of normal coordinate calculations for stable conformer of the molecule. HF results without scaled quantum mechanical (SQM) force field procedure considered are in bad agreement with experimental values. Of the two DFT methods, BLYP reproduces the observed fundamental frequencies most satisfactorily with the mean absolute deviation of the non-CH stretching modes less than 21.3 cm(-1). The results indicate that BLYP calculation is a very promising approach for understanding the observed spectral features.     

南四湖水中多环芳烃的分析及分布研究

采用固相萃取结合气相色谱-质谱(GC-MS)方法对南四湖水中13种多环芳烃进行了分析。南四湖水中检出的多环芳烃以二环、三环为主,检出的6种多环芳烃中相对含量较高的是菲、芴和苊,多环芳烃总浓度范围为0.004~3.53μg/L。入湖河口各点浓度比湖内点位低,上级湖的入湖河口含量高于下级湖的入湖河口,且湖内各点位多环芳烃的含量按湖水流向逐渐降低。     

Density functional theory study of the hydrogen bonding interaction of 1:1 complexes of serine with water

The hydrogen bonding of 1:1 complexes formed between serine and water molecules were completely investigated in the present study employing ab initio and Density Functional Theory (DFT) methods at varied basis set levels from 6‐31g to 6‐311++g (2d,2p). For comparison, we also used the second‐order Moller–Plesset Perturbation (MP2) method at the 6‐31+g(d) level. Twelve reasonable geometries on the potential energy hypersurface of serine and water system were considered with the global minimum, 10 of which are cyclic double‐hydrogen bonded structures and the other two are one‐hydrogen bonded structures. The optimized geometric parameters and interaction energies for various isomers at different levels were estimated. The infrared spectrum frequencies, IR intensities, and the vibrational frequency shifts are reported. Finally, the solvent effects on the geometries of the serine–water complexes were also investigated using self‐consistent reaction‐field (SCRF) calculations at the B3LYP/6‐311++g(d,p) level. The results indicate that the polarity of the solvent played an important role in the structures and relative stabilities of different isomers. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Density functional theory study of vibrational spectra of acridine and phenazine

Density functional theory (DFT) calculations using Becke's exchange in conjunction with Lee-Yang-Parr's correlation functionals (BLYP), Becke's three-parameter hybrid DFT/HF method using Lee-Yang-Parr's correlation functionals (B3LYP) and ab initio Hartree-Fock (HF) method have been carried out to investigate the structure and vibrational spectra of acridine and phenazine. Structural parameters obtained by B3LYP/6-31G* geometry optimization are in good agreement with available experimental data. The raw BLYP non-CH stretching frequencies approximate the experimental results much better than the HF results with the mean absolute deviation about 16 cm(-1). The scaled B3LYP frequencies are more reliable than that of the BLYP and HF methods with the mean absolute deviation about 17 cm(-1). On the basis of the comparison between calculated and experimental results, assignments of fundamental vibrational modes are examined. Also the structure and vibrational frequencies are compared with those of anthracene, pyridine and benzene to study the similarities and differences.     

Density functional theory study of the interaction between formamide and uracil

The hydrogen bonding of complexes formed between the formamide and uracil molecule has been fully investigated in the present study using the density functional theory (DFT) method at varied basis set levels from 6‐31G to 6‐311++G(d,p). Eight stable cyclic structures with two hydrogen bonds involved in the interaction are found on the potential energy surface (PES). The four structures are seven‐membered rings; the others are eight‐membered rings. The eight‐membered ring is preferred over the seven‐membered one by analyzing the hydrogen bond lengths and the interaction energies. The infrared (IR) spectrum frequencies, IR intensities, and the vibrational frequency shifts are reported. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Diastereoselective Synthesis of Monofluorocyclohexenes through Photocatalyzed Cascade Cyclization of gem-Difluoroalkenes and α,β-Unsaturated Carbonyl Compounds

Monofluoroalkenes are nonhydrolyzable mimetics of amides. Previous work focused on the synthesis of non-cyclic monofluoroalkenes. However, diastereoselective synthesis of monofluorocyclohexenes from non-cyclic substrates is challenging. Herein, we report the first photocatalyzed cascade cyclization reactions of readily available α,β-unsaturated carbonyl compounds and gem-difluoroalkenes for the synthesis of highly functionalized monofluorocyclohexenes. The reaction shows broad substrate scope with high diastereoselectivity (>30 examples, up to 86 % yield, >20 : 1 dr). The post-reaction transformations of the products demonstrate the synthetic potential of this methodology.     

Model smoke stream adsorption over cellulose acetate stick with three-dimensional temperature gradient by combining in-situ DRIFTS with infrared thermal imaging

Cellulose - Understanding the adsorption of the smoke stream (SR) on cigarette filter—cellulose acetate stick with different temperatures is beneficial for controlling chemical emissions and...     

Synthesis of Cyclic Vinylidene Complexes and Azavinylidene Complexes by Formal [4+2] Cyclization Reactions

Reactions of the hydrido‐butenylcarbyne complex [OsHCl₂(≡CC(PPh₃)=CHEt)(PPh₃)₂]BF₄ ( 1 ) with nitriles RC≡N (R=2‐cyclopropyl‐2‐oxopropyl, 3‐amino‐2‐oxobutyl) lead to six‐membered cyclic vinylidene complexes 3 and azavinylidene complexes 4 , that is, iso‐osmapyridiniums. Treatment of 1 with excess 2‐formylbenzonitrile at reflux temperature in CHCl₃ in the presence of air produces a fused osmapyridinium 8 , which is first oxidized to the tricyclic iso‐osmapyridinium derivative 7 , then to iso‐osmapyridinium 9 , which contains a fused naphthalenone fragment. The conversion of iso‐osmapyridinium 9 (with a vinylidene segment) to the iso‐osmapyridinium compounds 10 and 11 (with azavinylidene segments) was achieved in the presence of a hydrogen halide, such as HCl or HI. The molecular structures of the complexes synthesized were confirmed by X‐ray studies. Moreover, the aromatic stabilization energy and nucleus‐independent chemical‐shift values of the osmapyridiniums and the strain in the iso‐osmapyridinium rings were investigated by DFT calculations.     

A generalized Shimura correspondence for newforms

We associate a set of half integral weight forms to an integral weight newform of odd level. We prove an explicit identity relating the central values of the twist L-functions of the newform to the Fourier coefficients of the half integral weight forms.