HS-SPME-GC-MS/MS联用分析莲蓉馅料的特征挥发性香气成分

采用顶空固相微萃取气相色谱串联质谱法（HS-SPME-GC-MS/MS）对5种莲蓉馅料的挥发性物质进行研究,共检测到醇类（7.07%~9.72%）2种,醛类（18.38%~36.45%）7种,酯类（9.97%~23.88%）6种,吡嗪类（19.07%~29.38%）4种,烷烃类（1.31%~5.29%）3种,呋喃类（1.53%~4.88%）2种,酮类（2.78%~3.62%）2种,萜类（0%~10.82%）1种,噻吩类（0.04%~0.31%）1种,其他类（11.11%~16.21%）1种。通过PLS-DA模型与方差分析法筛选出不同莲蓉馅料的主要差异物质为糠醛、E,E-2,4-癸二烯醛、(±)-3-蒈烯-2,5-二酮、苯甲醛、正壬醛、2,6-二甲基吡嗪、3-甲基苯甲醛和十四烷。根据相对香气活度值（ROAV）评判莲蓉馅料的主要挥发性风味物质,其贡献程度大小依次为E,E-2,4-癸二烯醛、辛酸乙酯、2-乙酰基噻吩、正壬醛、己醛、乙酸苯乙酯和苯乙醇。综合不同莲蓉馅料挥发性成分的主要差异物质和风味贡献程度分析得出,E,E-2,4-癸二烯醛、正壬醛和苯甲醛的相对含量是影响莲蓉馅料呈香的主要因素。该研究结果揭示了莲蓉馅料的风味轮廓,为其品质评价与标准化生产提供理论依据。     

A theoretical study of the tautomerism kinetics of 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one in the gas phase: NBO population and NICS analysis

The tautomerization reactions of the 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one studied by means of M06-2x and CBS-QB3 theoretical methods. The measured energy profiles are complemented with kinetic rate coefficients calculations using transition state theory (TST). In line with the optimized tautomers geometries using the CBS-QB3 method, the natural bond orbital (NBO) analysis reveals that the stabilization energies of non-bonding LP(e)_S8 to the σ*_N2–C3 antibonding orbitals increase from tautomers 1 to 2. Furthermore, the delocalization energies of LP(e)_S8→σ*_N2–C3 could explain the increase of LP(e)_S8 non-bonding orbitals occupancies in the tautomers 1 and 2 (2?>?1). The increase of LP(e)_S8→σ*_N2–C3 delocalizations could fairly explicate the kinetics of tautomeric pathways 1 and 2 (k_2?>?k₁). Moreover, the HOMO–LUMO energy gap is increased parallel with the decreasing of activation energy barriers. NBO results also show that the kinetics of these processes controlled using LP→σ* resonance energies. Furthermore, nucleus-independent chemical shift (NICS) indices show the calculated reaction and energy barriers are involved by changes in aromaticity characters as well as electron transfer from LP(e)_S8 to σ*_N2–C3 orbitals, thus these reactions are controlled from both thermodynamic and kinetic viewpoints by the changes aromaticity characters.     

Evaluation of the aromatic structure of coal tar pitch by solid and solution state n.m.r.

Rapid magic angle spinning has been used to obtain sideband-free high field ¹³C n.m.r. spectra of coal tar pitches in the solid state. However, the unfavourable cross-polarization and ¹H relaxation characteristics make it difficult to accurately estimate concentrations of quaternary aromatic carbon using the dipolar dephasing method. The concentrations of bridgehead aromatic carbon in the whole pitch and toluene-insoluble fraction investigated were deduced using a combination of solid and solution state n.m.r. and elemental analyses.     

The role of aromaticity and the pi-conjugated framework in multiporphyrinic systems as single-molecule switches

A systematic analysis of electron-transport characteristics for monomer, dimer, and tetramer multiporphyrinic systems is presented, to provide a thorough understanding of the structural dependence of electron transport related to the aromatic nature of the contact structure. Theoretical investigation shows that the electron-transport characteristics can be controlled by manipulating the pi-conjugated framework in the multiporphyrinic systems through the arrangement of the inner hydrogen atoms. The designed pi-conjugated framework assigns the distinct aromaticity on the contact structure, and the large aromatic nature of the contact structure increases conductivity. The feature emerging from this study is that the aromaticity and pi-conjugated framework are important factors that control the electron-transport characteristics in molecular-scale electronic devices, such as single-molecule switches.     

POLYCYCLIC AROMATIC HYDROCARBON BOWLS,BASKETS, BALLS,AND TUBES: CHALLENGING TARGETS FOR CHEMICAL SYNTHESIS

The number of unique chemical substances registered by the Chemical Abstracts Service passed the 50 million mark in September 2009. The vast majority of these substances were brought into existence by chemical synthesis, a human activity that has grown immensely powerful and continues to advance at an ever-accelerating pace. It would not be unreasonable for the average layman to assume that chemists must now be able to synthesize everything imaginable; however, that Utopian level of success has not been achieved. Some molecular targets remain beyond the reach of chemical synthesis by present day methods. When fullerenes and carbon nanotubes were discovered near the end of the 20th century, for example, scientists quickly recognized that chemical methods to synthesize such large, curved, polycyclic aromatic structures simply did not exist. Since that time, progress has been made on the development of methods for this purpose, and the present article recounts some of the advances along those lines that have been made in the author’s laboratory.     

Structural and Molecular Orbital Studies of Si-Phenyl Silaanthracenes

The Si-phenyl derivatives of 1-, 2-, 9- silaanthracenes have been subjected to theoretical analysis with density functional theory (B3LYP/6-31G(d)) to obtain their molecular orbital properties. 2-silaanthracene has been found to be thermodynamically the most stable derivative among the trio. Moreover, the effects of the position of the Si substitution and phenyl attachment on the aromaticity of the parent anthracene have been investigated by NICS calculations at ring centers. The structures have been found to be less aromatic with respect to their unsubstituted counterparts.     

The Synthesis of Energetic Compound on 4,4′‐((2,4,6‐trinitro‐1,3‐phenylene)bis(oxy)) bis(1,3‐dinitrobenzene)(ZXC‐5): Thermally Stable Explosive with Outstanding Properties

The novel, thermally stable explosive 4,4′‐((2,4,6‐trinitro‐1,3‐phenylene)bis(oxy))bis(1,3‐dinitrobenzene) (Be referred to as ZXC‐ 5 in our laboratory) has been reported. ZXC‐5 can be synthesized by a simple synthetic method (The total synthesis of ZXC‐ 5 requires only two steps and the total yield of ZXC‐ 5 is more than 89 %) and shows the superior detonation performances (detonation pressure, detonation velocity, sensitivity toward mechanical stimuli, and temperature of decomposition). The structure of ZXC‐5 was characterized by multinuclear (¹H, ¹³C) NMR and mass spectrometry. The structure in the crystalline state was confirmed by low‐temperature single‐crystal X‐ray diffraction. From the calculated standard molar enthalpy of formation and the measured densities, the detonation properties were predicted by using the EXPLO5 V6.01 thermochemical computer code. The sensitivity of ZXC‐ 5 towards impact, electrostatic discharge, and friction were also measured.     

Carbonization of petroleum feedstocks II: Chemical constitution of feedstock asphaltenes and mesophase development

The characterization of the asphaltene fractions of a range of petroleum feedstocks by FT-IR, ¹H and ¹³C NMR spectroscopy indicated distinct differences in the molecular structure of the asphaltenes. Some of these differences could be related to the variations in the size of the principal optical texture of the semi-cokes produced by carbonization. The principal optical texture size was observed to increase steadily with the increasing hydrogen aromaticity of the asphaltenes over the whole range of the feedstocks used. There was no consistent correlation, however, between the carbon aromaticity of the asphaltenes and the optical texture size. The correlation between the hydrogen aromaticity and the principal optical texture size was attributed to structural differences among the asphaltenes that are critically important for the mesophase development.     

C40H2各种可能异构体芳香性的研究

用键共振能(BRE)和拓扑共振能(TRE)方法,对由从富勒烯C_(40)(D_(5d))产生的富勒烯氢化物C_(40)H_2H所有可能异构体的芳香性进行了研究。研究了氢原子加成位置和芳香性之间的关系。计算结果表明,氢原子的加成位置与C_(40)(D_(5d))中各键的键共振能直接有关。在C_(40)(D_(5d))中C3类碳原子具有最大的反应活性。大部分C_(40)H_2异构体的芳香性高于C_(40)。用拓扑共振能方法得到的C_(40)H_2异构体的稳定性顺序与AM1和PM3半经验方法得到的稳定性顺序是一致的,用键共振能和拓扑共振能方法同样地能预测富勒烯氢化物的稳定性。     

异质富勒烯C26BN各种可能异构体的芳香性和动力学稳定性研究

用拓扑共振能（TRE）和百分拓扑共振能（%TRE）方法,对由富勒烯C₂₈（T_d）产生的C₂₆BN各种可能异构体和它们阴离子的芳香性进行了研究。探讨了C₂₆BN异构体稳定性与杂原子取代位置间的关系。最后,用最小键共振能（min BRE）方法对C₂₈（T_d）和C₂₆BN分子离子的动力学稳定性进行了研究。研究结果表明C₂₈（T_d）和C₂₆BN在中性状态下,因TRE为负值被预测为具有反芳香性。Min BRE方法研究结果证明了C₂₈（T_d）和C₂₆BN的动力学不稳定性与分子中具有较高反芳香性键直接有关。TRE和min BRE方法研究结果表明,C₂₈^4-和C₂₆BN^4-各异构体不仅具有较高的芳香性而且也有较高的动力学稳定性。