共查询到20条相似文献，搜索用时 265 毫秒
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李宝宗 《实验室研究与探索》2010,29(4)
构象分析是阐明分子结构的最重要手段之一,理论计算能够给出分子构象异构的一般信息。采用HF/6-31G*、B3LYP/6-31G*、BHHLYP/6-31G*和MP2/6-31G*方法,对3种联吡咯构造异构体进行了构象分析。采用BHHLYP/6-31++G**方法进行势能面上稳定点和过渡态的计算。结果表明,气相中6个联吡咯能量极小构象体能量差最大达14.56kJ/mol,转化能垒最大达10.19kJ/mol。采用自洽反应场极化连续模型溶剂理论,探讨了水溶剂对优势构象异构体的几何结构和能量的影响。结果表明,水相中6个联吡咯能量极小构象体的能量差最大达9.40kJ/mol,转化能垒最大达11.68kJ/mol。这种系统化研究有助于理解联吡咯各构造异构体之间构象能量与几何结构的关系。 相似文献
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利用密度泛函方法(B3LYP、B3PW91、B3P86、PBE0)结合6-311G**基组和完全基组(CBS-Q)方法计算了15种巯基化合物的键离解能。结果表明,CBS-Q和B3P86是计算巯基化合物键离解能的可靠方法。为了检验非局域BLYP方法是否适合研究巯基化合物的键离解能以及B3P86方法是否对基组敏感,利用BLYP/6-31+G*方法和B3P86方法结合6-31+G*、6-31+G**和6-311+G**基组,计算了7种巯基化合物的键离解能,并将所得结果与实验结果进行了比较,研究发现B3P86方法对基组不敏感。考虑到CBS-Q方法的计算成本和B3P86计算的可靠性,B3P86方法结合适中的或较大的基组可以准确计算巯基化合物中C-SH键的离解能。 相似文献
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利用密度泛函理论方法(B3LYP、B3PW91、B3P86),使用6-31G**和6-311G**基组计算了13个取代氯化苯化合物的键离解能。结果表明,使用的计算方法和基组对计算C-Cl键离解能影响很大,且B3P86/6-311G**方法是计算含C-Cl键的取代氯苯化合物键离解能的最可信的方法。进一步讨论了取代基效应对取代氯苯化合物C-Cl键离解能的影响,结果表明取代基效应对取代氯苯化合物C-Cl键离解能的影响非常小。 相似文献
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采用B3LYP/6-311++G**方法和基组对外电场下CH4分子的性质进行了一系列的研究,包括分子的基态结构、电偶极矩、总能量、HOMO能级、LUMO能级、能隙Eg、红外与拉曼光谱性质和C-H键的解离特性.结果表明：随着加在C-H键轴方向的外电场增加,CH4分子中的C-H键长明显变长,能隙随着外电场的增加而减小;外电场对分子的红外与拉曼振动频率和振动强度都有重大影响.CH4分子的红外和拉曼光谱在外电场下都发生了重叠谱线的分裂和红移现象.随着外加电场的增强,分子中C-H键的势能曲线发生变化,势阱深度随外电场强度的增大而减小直至消失,分子趋向于解离. 相似文献
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用杂化密度泛函B3P86方法配合6-311G**和6-31 G**两个基组计算出离解掉硝基苯,3-胺基-硝基苯,4-胺基-硝基苯,1,3-二硝基苯,1,4-二硝基苯,2-甲基-硝基苯,4-甲基-硝基苯和1,3,5-三硝基苯中的二氧化氮自由基的键离解能,并将计算的键离解能值与实验值进行比较.研究发现,B3P86/6-311G**方法能计算出满意的键离解能. 相似文献
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在6-311G基组水平上,用B3LYP、HF和MP2三种方法对4-(2-氯苯基)-6-甲基-5-乙氧羰基-3,4-二氢嘧啶-2-酮进行了几何全优化,并对其电荷分布、前线分子轨道、成键情况以及自然键轨道(NBO)进行了分析.计算结果表明:HF方法得到的分子构型与实验值最为接近,标题化合物中嘧啶环为船式构象.标题化合物的稳定性较差,可能具有很好的生物活性.嘧啶环中2个氮原子的孤对电子都与相邻键有强的相互作用. 相似文献
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采用还原胺化法将苏氨酸成功转变成了其氮二甲基衍生物,通过1H-NMR和13C-NMR证实了其结构,采用量子化学方法在DFT-B3LYP/6-31G*水平上计算了该化合物的反应热、电荷分布和前线轨道能级。 相似文献
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采用B3LYP/6-31++G**方法对5-氯-6-苯基-2H-哒嗪-3-酮分子进行结构优化及频率计算,获得红外光谱、拉曼光谱、电子吸收光谱和不同温度下的热力学性质.结果显示,该分子的哒嗪环和苯基环不在同一个平面上,有-175.5°的二面角存在,整个分子不具有对称性;该分子的气态热容、熵、焓等热力学性质与温度之间存在很好的函数关系式. 相似文献
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采用不同方法、在不同基组水平上系统地对（NH3）2缔合体进行构型优化和结合能计算,并和实验值做详细比较。（1）对于弱氢键体系（NH3）2,B3LYP和HF计算结果不可靠;（2）适合（NH3）2体系的最好计算方案是MP2／6．311＋＋G＊＊（如果基组不低于6-31＋＋G＊＊水平,计算结果也可取）,但是必须做BSSE校正。（3）基组中不加弥散函数只能得到一种环状构型,加入弥散函数可以得到两种构型。（4）对于弱相互作用体系,在选用计算方法和基组前应该做充分的方法验证。 相似文献
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《海外英语》2007,(5):10-11
Many college freshmen arrive woefully unprepared to do college work, and as disadvantaged populations continue to grow, the share of the American work force that has made it through college is expected to plummet. Many experts blame that educational failure not just on high schools but also on colleges. School & College, a special report by The Chronicle, looks at efforts to fix the system. What reforms would better prepare students for college? What should schools and colleges be doing differently? How should state and federal officials help? 相似文献
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罗艳萍 《读与写:教育教学刊》2008,5(6)
The communication of people partially is the communication of cultures. Culture has a direct effect on international commercial activities in all aspects. Different conceptions about time, space, equality, law and the like, lead people to deal with things in different ways. So to know cultures of the counterpart is to facil-itate our enterprises so as to have a smooth and successful communication in commercial activity. 相似文献
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《海外英语》2007,(4):36
There are numbers of crossroads on our long and unpredictable life journey where we totally have no idea about which direction to choose. No matter what our decision is, we should not turn back, but face the music and go ahead instead. I am this kind of girl who always does try without regretting, one example is how I dealt with my love. 相似文献
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Migration occurs behind a variety of reasons and has a great effect on the whole world. People may migrate in order to improve their economic situation, or in order to escape civil strife, persecution, and environmental disasters. The impact of migration is complex, bringing both benefits anddisadvantages. This paper briefly talks about the causes of migration, the allocation of benefits, and the ways in which individual countries and the international community deal with this important subject. 相似文献
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Richard Denner 《海外英语》2007,(4):14-15
Rosco and I wait for the fishermen to return.I sit at a wooden bench near the store at Mt.Baker Resort and watch the clouds change shape. Rosco has my belt around his neck and an eight foot tow chain hooked to a tree. Dogs must be on a leash. Ducks and rabbits are loose. 相似文献
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Given a graph G,a subgraph C is called a clique of G if C is a complete subgraph of G maximal under inclusion and |C|≥2. A clique-transversal set S of G is a set of vertices of G such that S meets all cliques of G. The clique-transversal number, denoted as TC (G), is the minimum cardinality of a clique-transversal set in G. The clique-graph of G, denoted as K (G), is the graph obtained by taking the cliques of G as vertices, and two vertices are adjacent if and only if the corresponding cliques in G have nonempty intersection. Let F be a class of graphs G such that F={G|K(G) is a tree}. In this paper the graphs in F having independent clique-transversal sets are shown and thus TC (G)/|G|≤1/2 for all G ∈ F. 相似文献
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Sister Carrie is one of the most controversial characters in American literature.Thought as a "fallen woman" firstly,she was defined as a "new woman" by some critics later. However, by digging into the motivaton behind the whole process of Carrie's "success", the relationship between Carrie and her creator (the author), the social conditions of then American, it can be found that Carrie has never been free-standing on her thought and she has never found her real-sdf even after becoming a famous actress. In a society dominated by mass consumerism Carrie is only an adherent of her own desires. She also is a representative of all those country girls flooded into cities, a symbol and a sacrifice of the urbanization of America in a time countryside was overcome by cities. 相似文献