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用改造的重叠模型多重散射X~α自洽场方法计算环芳类化合物[2~3]cyclophanes的电子结构, 分析该类分子中分子轨道通过空间和通过键的相互作用,单键连接桥.双键连接桥对通过键相互作用的影响, 用过渡态理论方法计算分子前线分子轨道的电离能,理论结果与紫外光电子能谙符合较好. 相似文献
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用从头算HF/3-21+G*优化了二氮双环[m,n,l]游离基阳离子(m,n,l≥2~5).分子[4,4,4]和[2,2,2]+,[3,3,3]+,[4,4,4]+游离基阳离子的优势构型有D3对称性,而其它游离基阳离子的优势构型为非对称性.通过比较这些阳离子几何构型,HOMO和NHOMO(即Next HOMO和HOMO-1),和由MNDO计算确定的原子对作用能,表明当二氮双环游离基阳离子的桥链(CH2)n的n≥3时,桥头氮原子通过空间相互作用形成了一个弱的N,N'-三电子σ-键.形成的三电子键强度不随环的扩大而增强.而三电子键强度被两个因素影响:一个是桥头氮原子间的p轨道重叠的取向;另一个是它们相应p轨道成分. 相似文献
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首次报道了N-(2-澳乙基)咔唑和N-乙烯基咏唑的气相Hel紫外光电子能谱(UPS),借助于Gaussian 94采用RHF/6-3lG基组优化几何构型,并用RHF/6-31G基组计算分子轨道及能级.在对咔唑和N-烷基咔唑系列分子UPS电离能变化规律研究的基础上,对这2个分子的UPS谱带给予指认,并讨论其电子结构.结果表明N-(2-溴乙基)咔唑的UPS谱与N-烷基咔唑的不同之处是在10.295,10.540Ve处出现2个Br原子的孤对轨道;N-乙烯基咔唑的UPS谱带与咔唑的相比,电离能变化的特殊性说明乙烯基与咔唑环共平面. 相似文献
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首次系列报道了9-H咔唑及其系列N-取代衍生物的气相HeI紫外光电子能谱,借助于Gauss-94采用RHF/3-21G基组对它们的几何构型进行优化,并用RHF/6-31G基组计算分子轨道及能级,计算的分子轨道特征和能量很好地反映了各谱带的特点和分子间电离能的变化规律.依计算结果,以及同系列分子间谱带及相应电离能的相互比较,对每个分子的UPS谱带给予指认,讨论了N-烷基化对π分子轨道的选择性去稳定化作用,并讨论了分子之间电离能的变化规律,得到一系列有益的结论. 相似文献
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用MP2方法和B3LYP方法,在6-31G(d,p)基组下对复合物环硼氮烷-HCl体系和环硼氮烷-CHCl3体系进行优化,研究了其分子间氢键的本质.计算结果表明,氯仿与环硼氮烷分子之间的相互作用使C-H键长缩短,振动频率增大(蓝移),而HCl与环硼氮烷分子之间的相互作用使H-Cl键长增长,振动频率减小(红移).自然键轨道(NBO)分析表明,影响氢键红移和蓝移主要有3个因素:n(Y)→σ*(X-H)超共轭作用、X-H键轨道再杂化和质子供体电子密度重排.其中,超共轭作用属于键伸长效应,电子密度重排和轨道再杂化属于键收缩效应.环硼氮烷-HCl体系的构型1和2伸长效应处于优势地位导致形成红移氢键;环硼氮烷-CHCl3体系中,由于键收缩效应处于优势地位导致形成蓝移氢键. 相似文献
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首次报道了N-(2-溴乙基)咔唑和N-乙烯基咔唑的气相HeI紫外光电子能谱(UPS),借助于Gaussian94采用RHF/6-31G基组优化几何构型,并用RHF/6-31G^*基组计算分子轨道及能级.在对咔唑和N-烷基咔唑系列分子UPS电离能变化规律研究的基础上,对这2个分子的UPS谱带给予指认,并讨论其电子结构.结果表明N-(2-溴乙基)咔唑的UPS谱与N-烷基咔唑的不同之处是在10.295,10.540eV处出现2个Br原子的孤对轨道;N-乙烯基咔唑的UPS谱带与咔唑的相比,电离能变化的特殊性说明乙烯基与咔唑环共平面。 相似文献
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Ione pair orbital and their interaction in some nitrogen heterocyclic compound series have been interpreted in terms of through-space and through-bond mechanisms through the study of their gas phase ultraviolet photoelectron spectrocopy. The HAM/3 molecular orbital calculations on each molecule of the studied series were also carried out. The order of experimental vertical ionization potentials of the molecules can be not only predicated, but the spacing of through-space and through-bond interactions splitting of the studied compounds are consistent with the results of HAM/3 calculations. 相似文献
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人们知道,原子和分子的气相紫外光电子能谱(UPS)谱带的分离结构是电子能级量子化的反映.谱峰相应的电子结合能(或电离能)是正则(自洽场)分子轨道计算方法给出的本征值(-ε_i),所以UPS是目前用以获得原子或分子能级直接量度的最好技术.就是说:量子化学理论可以提供UPS解译的必要模型,而UPS谱本身反过来又可以检验分子轨道理论的正确性,并作为各种近似分子轨道理论计算中经验参数化(如SPINDO)的基础.因而UPS 相似文献
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The gas-phase conformation of the title compound (1) is discussed in reference to its photoelectron spectrum. The experimental lone-pair/lone-pair splitting (0.51 eV), when compared with that of similar diamines and with the results of three sets of MO calculations (MINDO/3, MNDO and STO-3G), leads to the conclusion that 1 exists in the chair-chair conformation. A remarkable sensitivity of the calculations to slight changes in the geometry is noted, and it is suggested that calculations of this type must include geometry-optimization. The question of through-space vs through-bond inteaction of the nitrogen lone pairs was explored by performing MNDO calculations in which the N-N resonance integrals were set to zero. These calculations indicate that in the chair-chair conformation the N-N interaction is mainly through-space. The 13CNMR and Ni(acac)2-induced 13C shifts of 1 are discussed. 相似文献
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Flemming S Jørgensen Leif Nørskov-Lauritsen Roald Boe Jensen Gustav Sshroll 《Tetrahedron》1981,37(21):3671-3679
The photoelectron (PE) spectrum of cis-1,4,5,8-tetraoxadecalin exhibits in contrast to most polyoxa compounds an extremely well resolved low energy pan due to large ‘through-bond’ interactions between the oxygen lone pairs and the ideally oriented C-C bonds. The ‘through-bond’ interactions of the cis- as well as the unknown trans-1,4,5,8-tetraoxadecalin are discussed based on simple perturbation molecular orbital theory and PRDDO molecular orbital calculations. Additionally the PE spectrum of 2,2'-bis (1,3-dioxolane) is reported. Molecular mechanics (MM1 and MM2) and molecular orbital (PRDDO) calculations of the different conformations of the 1,4,5,8-telraoxadecalin and 2,2'-bis(1,3-dioxolane) systems allow the absence of the trans-1, 4,5,8-tetraoxadecalin, and the cis-trans energy difference in the series decalin, 1,8-dioxadecalin and 1,4,5,8-tetraoxadecalin systems to be explained. 相似文献
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Arulmozhiraja S Coote ML Lu D Salem G Wild SB 《The journal of physical chemistry. A》2011,115(17):4530-4534
This paper presents a combined experimental and theoretical study of the electronic spectrum of the natural adamantane-type polyarsenical Arsenicin A. Experiments reveal that this molecule strongly absorbs UV light in the absence of an obvious chromophore. The observed absorbance is supported by the time-dependent density functional (TD-DFT) calculations with B3LYP, M06-L, and M06-2X functionals combined with the 6-311+G(3df,2pd) basis set, as well as by symmetry-adapted cluster/configuration interaction (SAC-CI) theory. The theoretical investigations reveal that the absorption is facilitated by through-space and through-bond interactions, between the lone pairs on the arsenic and oxygen atoms and the σ-bonding framework of the molecule, that destabilize occupied and stabilize unoccupied molecular orbitals. 相似文献
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Felicíssimo VC Cesar A Luo Y Gel'mukhanov F Agren H 《The journal of physical chemistry. A》2005,109(33):7385-7395
Carbon and oxygen near-edge X-ray absorption fine structure (NEXAFS) spectra of 1,4-cyclohexadiene, p-benzoquinone, norbornadiene, norbornadienone, and cis-cis-[4,4,2]propella-3,8-diene-11,12-dione were calculated by means of Hartree-Fock and hybrid density functional theory using the static-exchange (STEX) approximation. The NEXAFS spectra are used as a probe to identify weak molecular interactions between the two non-conjugated ethylenic pi* orbitals present in these molecules. We show that the X-ray absorption spectrum of 1,4-cyclohexadiene exhibits some particular spectral structures in the discrete energy region that evidence diene through-bond orbital interaction, whereas absorption peaks are identified in the norbornadiene and norbornadienone spectra that indicate effective through-space orbital interactions. The molecular structure of the cis-cis-[4,4,2]propella-3,8-diene-11,12-dione isomer is such that the indirect through-bond or through-space diene orbital interactions are too weak to be assigned by its C1s NEXAFS spectrum. 相似文献
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F. Bernardi F.P. Colonna P. Dembech G. Distefano P. Vivarelli 《Chemical physics letters》1975,36(4):539-541
The UV photoelectron spectrum of [2,2] metacyclo-2,6-pyridinophane has been analyzed on the basis of a perturbational molecular orbital analysis and CNDO/2 calculations. Through space and through bond interactions are shown to be present between the two pyridine rings. In particular a strong interaction has been found between the nitrogen lone pairs and the π systems of the rings. 相似文献
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Photoelectron spectra of malonic, methylmalonic and diethylmalonic acids are reported. The energy splitting of photoelectron bands representing carbonyl oxygen lone pairs is due to a “through-bond” interaction mechanism. The magnitude of the splitting depends upon the α-alkyl substitution because of conformational effects. 相似文献
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Walter M. F. Fabian 《Journal of computational chemistry》1991,12(1):17-35
Tautomeric equilibria (mainly of the lactam-lactim type) for a rather large number of six-membered heterocyclic molecules are calculated by the semiempirical AM1, MNDO-PM3, and MNDO methods. Except for compounds with adjacent pyridine-like lone pairs both AM1 as well as MNDO-PM3 give rather reliable predictions for relative stabilities of the various tautomeric species–comparable to quite high level ab initio calculations. The known errors associated with MNDO in the treatment of heterocyclic tautomerism are thus largely corrected in AM1 as well as MNDO-PM3. For 2-hydroxypyridine-pyrid-2(1H)-one the effect of self-association is less satisfactorily described by MNDO-PM3 than by AM1. MNDO-PM3 calculated relative stabilities of methylated derivatives are, however, in considerably closer agreement with experimental values than those obtained by AM1. Ionization potentials, especially those for lone-pair orbitals, are overestimated by all three semiempirical methods. MNDO-PM3 results for nitrogen lone-pair orbital energies are slightly better than those obtained by the AM1 or MNDO method. 相似文献