The individual hydrogen bonding energies in N-methylacetamide chains were evaluated at the MP2/6-31+G** level including BSSE correction and at the B3LYP/6-311++G(3df,2pd) level including BSSE and van der Waals correct...The individual hydrogen bonding energies in N-methylacetamide chains were evaluated at the MP2/6-31+G** level including BSSE correction and at the B3LYP/6-311++G(3df,2pd) level including BSSE and van der Waals correction.The calculation results indicate that compared with MP2 results,B3LYP calculations without van der Waals correction underestimate the individual hydrogen bonding energies about 5.4 kJ m ol-1 for both the terminal and central hydrogen bonds,whereas B3LYP calculations with van der Waals correction produce almost the same individual hydrogen bonding energies as MP2 does for those terminal hydrogen bonds,but still underestimate the individual hydrogen bonding energies about 2.5 kJ mol-1 for the hydrogen bonds near the center.Our calculation results show that the individual hydrogen bonding energy becomes more negative (more attractive) as the chain becomes longer and that the hydrogen bonds close to the interior of the chain are stronger than those near the ends.The weakest individual hydrogen bonding energy is about-29.0 kJ m ol-1 found in the dimer,whereas with the growth of the N-methylacetamide chain the individual hydrogen bonding energy was estimated to be as large as-62.5 kJ mol-1 found in the N-methylacetamide decamer,showing that there is a significant hydrogen bond cooperative effect in N-methylacetamide chains.The natural bond orbital analysis indicates that a stronger hydrogen bond corresponds to a larger positive charge for the H atom and a larger negative charge for the O atom in the N-H···O=C bond,corresponds to a stronger second-order stabilization energy between the oxygen lone pair and the N-H antibonding orbital,and corresponds to more charge transfer between the hydrogen bonded donor and acceptor molecules.展开更多
N-methylacetamide（NMA） was used as entrainer in separating acetic acid from water with extractive distillation,and the interaction mechanism in this process was studied by using the density functional theory.The opt...N-methylacetamide（NMA） was used as entrainer in separating acetic acid from water with extractive distillation,and the interaction mechanism in this process was studied by using the density functional theory.The optimization geometries and vibration frequencies of NMA-acetic acid and NMA-water complexes were calculated at the B3LYP/6-311G（d,p） level.After the basis set superposition error（BSSE） correction and the zero point vibration energy（ZPE） correction,the interaction energies for three types of NMA-acetic acid complexes and one type of NMA-water complex were-44.3,-35.5,（-32.4） and-16.0 kJ·mol-1 respectively,which showed that NMA had a great affinity for acetic acid than water.The boiling point of the NMA-acetic acid complex was higher than that of acetic acid so that acetic acid is easily preserved in the liquid phase,which is in agreement with the VLE experiment for NMA+acetic acid+water system that gave a relative volatility of 3.0—4.0.The results of natural bond orbital（NBO） population analysis revealed that there was charge-transfer in the complex formation,and acetic acid acted as electron acceptor during this transformation.展开更多
基金supported by the National Natural Science Foundation of China (20973088, 20633050)the research fund of the Educational Department of Liaoning Province (2007T091)
文摘The individual hydrogen bonding energies in N-methylacetamide chains were evaluated at the MP2/6-31+G** level including BSSE correction and at the B3LYP/6-311++G(3df,2pd) level including BSSE and van der Waals correction.The calculation results indicate that compared with MP2 results,B3LYP calculations without van der Waals correction underestimate the individual hydrogen bonding energies about 5.4 kJ m ol-1 for both the terminal and central hydrogen bonds,whereas B3LYP calculations with van der Waals correction produce almost the same individual hydrogen bonding energies as MP2 does for those terminal hydrogen bonds,but still underestimate the individual hydrogen bonding energies about 2.5 kJ mol-1 for the hydrogen bonds near the center.Our calculation results show that the individual hydrogen bonding energy becomes more negative (more attractive) as the chain becomes longer and that the hydrogen bonds close to the interior of the chain are stronger than those near the ends.The weakest individual hydrogen bonding energy is about-29.0 kJ m ol-1 found in the dimer,whereas with the growth of the N-methylacetamide chain the individual hydrogen bonding energy was estimated to be as large as-62.5 kJ mol-1 found in the N-methylacetamide decamer,showing that there is a significant hydrogen bond cooperative effect in N-methylacetamide chains.The natural bond orbital analysis indicates that a stronger hydrogen bond corresponds to a larger positive charge for the H atom and a larger negative charge for the O atom in the N-H···O=C bond,corresponds to a stronger second-order stabilization energy between the oxygen lone pair and the N-H antibonding orbital,and corresponds to more charge transfer between the hydrogen bonded donor and acceptor molecules.
文摘N-methylacetamide（NMA） was used as entrainer in separating acetic acid from water with extractive distillation,and the interaction mechanism in this process was studied by using the density functional theory.The optimization geometries and vibration frequencies of NMA-acetic acid and NMA-water complexes were calculated at the B3LYP/6-311G（d,p） level.After the basis set superposition error（BSSE） correction and the zero point vibration energy（ZPE） correction,the interaction energies for three types of NMA-acetic acid complexes and one type of NMA-water complex were-44.3,-35.5,（-32.4） and-16.0 kJ·mol-1 respectively,which showed that NMA had a great affinity for acetic acid than water.The boiling point of the NMA-acetic acid complex was higher than that of acetic acid so that acetic acid is easily preserved in the liquid phase,which is in agreement with the VLE experiment for NMA+acetic acid+water system that gave a relative volatility of 3.0—4.0.The results of natural bond orbital（NBO） population analysis revealed that there was charge-transfer in the complex formation,and acetic acid acted as electron acceptor during this transformation.
