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21.
用从头算对丙烯和甲苯2个超共轭体系进行计算,结果表明甲基上氢原子参与超共轭时,其碳氢键键长增大,氢上集居数减少,丙烯、甲苯的甲基旋转势垒为7.61及0.096 kJ/mol.超共轭基作用相当于一带有孤对电子参与共轭之杂原子,超共轭体系不同构型稳定性可用M=sum from i=1 to 3(sinθ_i[sin(θ_i-α)+sinα])来表征。 相似文献
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Key aspects of the microenvironment surrounding the Fe center in the nitrosyl adduct of iron phthalocyanine, [Fe(Pc)(NO)], have been elucidated from the analysis of the Fe K-edge extended X-ray absorption fine structure (EXAFS) of the material adsorbed on the surface of a high area carbon electrode recorded in situ, in 0.5 M H(2)SO(4). Statistical best fits to the EXAFS data place the Fe center in a five-coordinated square pyramidal configuration shifted away from the Pc plane toward the axially bound NO bent at an angle of ca. 40 degrees with respect to the normal to the Pc plane. This environment is analogous to that of Fe in the nitrosyl adduct of crystalline [Fe(TPP)], where TPP = meso-tetraphenylporphyrinato(2-), determined from X-ray diffraction. 相似文献
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Abstract —Using semi-empirical analytic formulas for the transmitted and scattered ultraviolet spectral irradiance at the ground (Green, A. E. S., T. Sawada and E. P. Shettle, Photochem. Photobiol. 19 , 251–259, 1974), we calculate erythema dose rates and daily erythema doses. Results are illustrated graphically, and for the purpose of photobiological applications are given in terms of approximate analytic forms, with parameters presented in tabular form. The relative erythema data assembled by W. W. Coblentz and R. Stair (U.S. Bureau of Standards J. Res. 12 , 13–14, 1934), as fit by an analytic form, is taken as a standard spectrum in our calculations. Other forms of erythema spectra are also compared. 相似文献
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Yiming Mo Yanfei Guan Pritha Verma Jiang Guo Mike E. Fortunato Zhaohong Lu Connor W. Coley Klavs F. Jensen 《Chemical science》2021,12(4):1469
With recent advances in the computer-aided synthesis planning (CASP) powered by data science and machine learning, modern CASP programs can rapidly identify thousands of potential pathways for a given target molecule. However, the lack of a holistic pathway evaluation mechanism makes it challenging to systematically prioritize strategic pathways except for using some simple heuristics. Herein, we introduce a data-driven approach to evaluate the relative strategic levels of retrosynthesis pathways using a dynamic tree-structured long short-term memory (tree-LSTM) model. We first curated a retrosynthesis pathway database, containing 238k patent-extracted pathways along with ∼55 M artificial pathways generated from an open-source CASP program, ASKCOS. The tree-LSTM model was trained to differentiate patent-extracted and artificial pathways with the same target molecule in order to learn the strategic relationship among single-step reactions within the patent-extracted pathways. The model achieved a top-1 ranking accuracy of 79.1% to recognize patent-extracted pathways. In addition, the trained tree-LSTM model learned to encode pathway-level information into a representative latent vector, which can facilitate clustering similar pathways to help illustrate strategically diverse pathways generated from CASP programs.Tree-structured long short-term memory neural model learns to understand the retrosynthesis design strategies from patent-extracted retrosynthetic pathway data. 相似文献
26.
Protonation of acylferrocenes (FeCOR) in FSO3H-SO2CIF(SO2) solution was studied by PMR spectroscopy. The site of protonation is found to be at the carbonyl oxygen atom. Temperature dependent PMR spectra of protonated acylferrocenes FeCROH+ (R = CH3, C2H5, C6H5, OCH3) were observed indicating intermolecular hydrogen exchange with the acid solvent system. In addition the PMR spectra of acylferrocenes in FSO3 H-SO2 CIF(SO2) were found to be dependent upon the acid concentration. 相似文献
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结晶聚合物中间层理论与实验佐证 总被引:3,自引:0,他引:3
概述了Flory和Yoon由晶格模型出发,从理论上证明了结晶聚合物中间层的存在以及近年来许多学者采用多种实验技术确认中间层存在的事实。 相似文献
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本文研究了二茂钛含氟长链有机酸衍生物(1~3)和具有环状结构的新型二茂钛全氟有机酸(4~7)的电子轰击质谱(EIMS)和负离子化学电离质谱(NICIMS)。在EI谱中出现弱的或不出现M~+,1~7均以CpTiF_2离子为基峰。高质量区的主要特征碎片离子有[M-·cp]~+、[M-R]~+(1~3)和氟重排离子。在低质量区出现一系列二茂钛及茂钛氟重排离子。 1、4~7的NICI(CH_4)质谱中,4、5出现强的M~-离子峰,1出现[M-1]-离子峰,有两个钛的环状结构化合物6和7出现双电荷M~=离子峰,而不出现M~-。 相似文献