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Ab initio valence bond method is employed to quantitatively study the concepts of ionic resonance energy and ionicity of a chemical bond in the cases of hydrides XH(X=Li,Be,B,C,N,O,F) and fluorides XF(X=Li,Be,B),By establishing the relationship between resonance and stability,and comparing the calculated ionicities with Pauling‘s earlier estimations in the above diatomic molecules,the merits of Pauling‘s classical resonance theory were demonstrated at the ab initio level. 相似文献
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脉冲相位的不稳定性是导致二维谱中的t1噪声的原因之一.本文从理论上和实验上对脉冲相位不稳定性所引起的t1噪声进行了研究.从角动量算符Ix,Iy和Iz推导中发现,由于磁化矢量在P型和N型DQF-COSY实验的脉冲梯度场中进动方向的内在差异,一部分脉冲相位误差在P型DQF-COSY实验会被重聚掉,在N型DQF-COSY实验中却会被加重.因此P型DQF-COSY实验的t1噪声比N型小.理论推导还得到t1噪声在P型和N型中的理论比值为√3:√11.以上理论结果得到我们实验结果的支持. 相似文献
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A scheme has been proposed to classify valence bond(VB) wave functions for the calculations of ground and excited states,according to the symmetry properties of one-electron orbitals which are involved in the construction of VB wave functions.This scheme is illustrated by the examples of BeH and BH.Ab initio VB computations of these two test molecules in combination with the present classification scheme give reliable results.For example,calculation results show that the state C2∑ of BeH is stable,with the bonding energy 0.87 eV and bond length 0.238nm,which are in good agreement with those obtained by Gerratt et al.The bonding features of ground and low-lying excited states of BeH and BH are discussed. 相似文献
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酸碱存在下水溶性铑膦配合物的NMR表征及氢甲酰化性能研究 总被引:1,自引:0,他引:1
31P(1H)NMR和1HNMR研究表明,当NaOH加入到水溶性铑膦配合物HRh(CO)·(TPPTS)3[TPPTS:P(m-C6H4SO3Na)3]后,可观察到有少量的OTPPTS[OTPPTS:O=P(m-C6H4SO3Na)3]出现,但配合物的特征谱峰即使在高浓度的NaOH存在下也基本保持不变,表明NaOH对配合物分子结构的影响较小;当吡啶加入到HRh(CO)(TPPTS)3中,31P(1H)NMR谱图中出现游离配体TPPTS的31P谱峰及若干结构未知的新水溶性配合物的31P谱峰,表明吡啶分子将与配合物分子中的配体TPPTS发生配体交换反应.在HRh(CO)(TPPTS)3中分别加入一定量的HCl,HNO3,H2SO4和H3PO4等无机酸时,随着酸量的增加,配合物的31P物种含量逐渐下降,而OTPPTS量明显上升,直至配合物31P物种完全消失;高浓度乙酸对配合物结构的影响与上述无机酸类似.HRh(CO)(TPPTS)3的1-己烯氢甲酰化催化反应结果表明,碱存在下可获得较高的正异构醛比值,但催化活性降低;酸存在下所得产物正异构醛比值相对较低且呈淡黄色. 相似文献
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高分辨NMR研究金属盐对水溶性铑膦配合物分子结构的影响 总被引:1,自引:0,他引:1
用高分辨NMR研究了NaCl、NiSO4、CuSO4、Fe2(SO4)3和Cr2(SO4)3对水溶性铑膦配合物HRh(CO)(TPPTS)3[TPPTS;P(m-C6H4SO3Na)3]分子结构的影响.31P(1H)和1HNMR谱显示,于室温下在HRh(CO)(TPPTS)3中加入的NaCl或NiSO4对配合物的特征31P(1H)和1HNMR谱峰无明显影响;当加入CuSO4后,配合物的Rh-H质子峰强度弱化明显,进而消失,且原配合物的特征磷谱峰强度减弱,新生成的磷物种谱峰逐渐成为磷谱的主要物种.当加入Fe2(SO4)3或Cr2(SO4)3后,三价金属离子的强顺磁性使NMR灵敏度下降,谱峰宽化,该2种盐均易与水溶性铑膦配合物产生强烈的相互作用,易使配合物特征谱峰消失.实验结果表明,上述金属盐对配合物结构破坏性大小的顺序为;Fe2(SO4)3>Cr2(SO4)3>CuSO4》NiSO4~NaCl. 相似文献
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The investigation on chemical reaction mechanism is one of the major activities and goals of the theoretical and computational chemistry. There have been considerable advances in recent years in developing high level methods to obtain accurate potential energy surface of small sys-tems, which provides not only detailed information on the reaction path (energetic, geometric, and electronic properties) but also good starting points for the prediction of thermodynamic as well as kinetic properties… 相似文献