Based on density functional theory and electronegativity equalization principle, a σπ model, which considers the structure of double bond for the first time, is developed. In this model the double bond is partitione...Based on density functional theory and electronegativity equalization principle, a σπ model, which considers the structure of double bond for the first time, is developed. In this model the double bond is partitioned into one σ bond region and four π bond regions. The atom bond electronegativity equalization method plus σπ model(ABEEM σπ ) is then proposed for the calculation of charge distribution and charge polarization in large molecules. It has been shown that the results of charge distribution in large molecules obtained by ABEEM σπ model agree with those obtained by ab initio method very well. In addition, the model can be used to explain the region selectivity of Diels Alder reaction successfully. All these indicate that ABEEM σπ model is reasonable and reliable.展开更多
用密度泛函理论和ONIOM(our own N-layer integrated molecular orbital molecular mechanics)方法研究磷改性的ZSM-5沸石中含磷基团的可能存在形态.计算的反应焓和自由能数据表明P-ZSM-5沸石中以磷进入骨架和在骨架外的形成磷酸根离子...用密度泛函理论和ONIOM(our own N-layer integrated molecular orbital molecular mechanics)方法研究磷改性的ZSM-5沸石中含磷基团的可能存在形态.计算的反应焓和自由能数据表明P-ZSM-5沸石中以磷进入骨架和在骨架外的形成磷酸根离子对是合理的稳定结构.而且,计算结果表明离子对模型F和G更适合在室温下存在,磷进入骨架的酸性结构C?在高温下更稳定,而磷进入骨架的结构C对温度变化不敏感.计算得到的27Al,31P,29Si化学位移、酸性的变化趋势和结构参数与相关实验数据吻合.展开更多
采用组合的量子化学ONIOM(our own n-layered integrated molecule orbit and molecule mechanics)(B3LYP/6-31++G(d,p):UFF)方法,研究了限域在SWBNNT(9,9)内α-丙氨酸的分子结构和手性转变通道.为得到高水平的能量,在ONIOM(B3LYP/6-311...采用组合的量子化学ONIOM(our own n-layered integrated molecule orbit and molecule mechanics)(B3LYP/6-31++G(d,p):UFF)方法,研究了限域在SWBNNT(9,9)内α-丙氨酸的分子结构和手性转变通道.为得到高水平的能量,在ONIOM(B3LYP/6-311++G(3df,3pd):UFF)水平,计算了各个包结物的单点能.分子结构分析表明:与单体α-丙氨酸相比,受限在SWBNNT(9,9)内时,骨架碳氮原子间的键长不同程度地缩短,骨架碳原子的键角及骨架碳氮原子的二面角略有增大.反应路径研究发现:α-丙氨酸分子在SWBNNT(9,9)内的手性转变有两条同单体情况大致相同的反应通道,不存在单体情况的含有羰基H和甲基H协同转移过程的反应通道.手性转变反应过程的势能面计算发现:与单体α-丙氨酸手性转变反应过程的主要能垒相比较,在纸外面的氢从手性碳直接到羰基氧的过渡态产生的能垒,从326.5kJ·mol-1降到319.7kJ·mol-1;氢首先在羧基内转移,而后手性碳的氢在纸面外转移到羰基,这两个过程的能垒从198.0kJ·mol-1和320.3kJ·mol-1降到135.5kJ·mol-1和302.7kJ·mol-1.结果表明:限域在SWBNNT(9,9)内的α-丙氨酸,其手性转变过程中不同的氢转移反应能垒被不同程度地降低.展开更多
文摘Based on density functional theory and electronegativity equalization principle, a σπ model, which considers the structure of double bond for the first time, is developed. In this model the double bond is partitioned into one σ bond region and four π bond regions. The atom bond electronegativity equalization method plus σπ model(ABEEM σπ ) is then proposed for the calculation of charge distribution and charge polarization in large molecules. It has been shown that the results of charge distribution in large molecules obtained by ABEEM σπ model agree with those obtained by ab initio method very well. In addition, the model can be used to explain the region selectivity of Diels Alder reaction successfully. All these indicate that ABEEM σπ model is reasonable and reliable.
文摘用密度泛函理论和ONIOM(our own N-layer integrated molecular orbital molecular mechanics)方法研究磷改性的ZSM-5沸石中含磷基团的可能存在形态.计算的反应焓和自由能数据表明P-ZSM-5沸石中以磷进入骨架和在骨架外的形成磷酸根离子对是合理的稳定结构.而且,计算结果表明离子对模型F和G更适合在室温下存在,磷进入骨架的酸性结构C?在高温下更稳定,而磷进入骨架的结构C对温度变化不敏感.计算得到的27Al,31P,29Si化学位移、酸性的变化趋势和结构参数与相关实验数据吻合.
文摘采用组合的量子化学ONIOM(our own n-layered integrated molecule orbit and molecule mechanics)(B3LYP/6-31++G(d,p):UFF)方法,研究了限域在SWBNNT(9,9)内α-丙氨酸的分子结构和手性转变通道.为得到高水平的能量,在ONIOM(B3LYP/6-311++G(3df,3pd):UFF)水平,计算了各个包结物的单点能.分子结构分析表明:与单体α-丙氨酸相比,受限在SWBNNT(9,9)内时,骨架碳氮原子间的键长不同程度地缩短,骨架碳原子的键角及骨架碳氮原子的二面角略有增大.反应路径研究发现:α-丙氨酸分子在SWBNNT(9,9)内的手性转变有两条同单体情况大致相同的反应通道,不存在单体情况的含有羰基H和甲基H协同转移过程的反应通道.手性转变反应过程的势能面计算发现:与单体α-丙氨酸手性转变反应过程的主要能垒相比较,在纸外面的氢从手性碳直接到羰基氧的过渡态产生的能垒,从326.5kJ·mol-1降到319.7kJ·mol-1;氢首先在羧基内转移,而后手性碳的氢在纸面外转移到羰基,这两个过程的能垒从198.0kJ·mol-1和320.3kJ·mol-1降到135.5kJ·mol-1和302.7kJ·mol-1.结果表明:限域在SWBNNT(9,9)内的α-丙氨酸,其手性转变过程中不同的氢转移反应能垒被不同程度地降低.
