Calculation of the Potential Energy Surface for Intermolecular Amide Hydrogen Bonds Using Semiempirical and Ab Initio Methods
详细信息 查看全文
- 作者：Helgi Adalsteinsson ; Andreas H. Maulitz ; and Thomas C. Bruice
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：August 21, 1996
- 年：1996
- 卷：118
- 期：33
- 页码：7689 - 7693
- 全文大小：224K
- 年卷期：v.118,no.33(August 21, 1996)
- ISSN：1520-5126
文摘
The dependence of hydrogen-bond interaction energiesbetween identical amides (two formamides andtwo N-methylacetamides) on the hydrogen bond length(rO···H), the two hydrogen bond angles(
hars/theta.gif" BORDER=0 >COH and hars/theta.gif" BORDER=0 >NHO), andthe dihedral between the two amides (hars/Phi.gif" BORDER=0 >CNCN) has beenassessed by semiempirical calculations (SAM1 with singlepoint transfers to AM1/SM2.1 aqueous solvation calculations).Ab initio calculations(MP2/6-31+G(d,p)//HF/6-31+G(d,p)) at given values of hars/Phi.gif" BORDER=0 >CNCN andhars/theta.gif" BORDER=0 >COH predict the same change in interaction energies withchanges inhars/theta.gif" BORDER=0 >NHO as the semiempirical calculations. Withformamide, hydrogen-bond interaction energies are independentofthe dihedral angle hars/Phi.gif" BORDER=0 >CNCN when hars/theta.gif" BORDER=0 >COH andhars/theta.gif" BORDER=0 >NHO deviate less than 40
from 180. Mostimportantly, the increasedinteraction energies at hars/theta.gif" BORDER=0 >COH and hars/theta.gif" BORDER=0 >NHO below140 and above 220 are found to be associated with stericinterferencebetween the carbonyl oxygen of the hydrogen-bond acceptor and the amidenitrogen of the hydrogen-bond donor.Comparing formamide and N-methylacetamide, the anglerequirements (hars/theta.gif" BORDER=0 >COH, hars/theta.gif" BORDER=0 >NHO, andhars/Phi.gif" BORDER=0 >CNCN) of favorable hydrogen-bond interaction energies are much more stringent for the latter due tothe steric effects of the methyl substituents.In summary, by both semiempirical SAM1 and ab initioMP2/6-31+G(d,p)//HF/6-31+G(d,p) calculations, thestrengthof amide hydrogen bonding in the absence of steric hindrance isessentially independent of the angles defining thehydrogen bond.
hars/theta.gif" BORDER=0 >COH and hars/theta.gif" BORDER=0 >NHO), andthe dihedral between the two amides (hars/Phi.gif" BORDER=0 >CNCN) has beenassessed by semiempirical calculations (SAM1 with singlepoint transfers to AM1/SM2.1 aqueous solvation calculations).Ab initio calculations(MP2/6-31+G(d,p)//HF/6-31+G(d,p)) at given values of hars/Phi.gif" BORDER=0 >CNCN andhars/theta.gif" BORDER=0 >COH predict the same change in interaction energies withchanges inhars/theta.gif" BORDER=0 >NHO as the semiempirical calculations. Withformamide, hydrogen-bond interaction energies are independentofthe dihedral angle hars/Phi.gif" BORDER=0 >CNCN when hars/theta.gif" BORDER=0 >COH andhars/theta.gif" BORDER=0 >NHO deviate less than 40 from 180. Mostimportantly, the increasedinteraction energies at hars/theta.gif" BORDER=0 >COH and hars/theta.gif" BORDER=0 >NHO below140 and above 220 are found to be associated with stericinterferencebetween the carbonyl oxygen of the hydrogen-bond acceptor and the amidenitrogen of the hydrogen-bond donor.Comparing formamide and N-methylacetamide, the anglerequirements (hars/theta.gif" BORDER=0 >COH, hars/theta.gif" BORDER=0 >NHO, andhars/Phi.gif" BORDER=0 >CNCN) of favorable hydrogen-bond interaction energies are much more stringent for the latter due tothe steric effects of the methyl substituents.In summary, by both semiempirical SAM1 and ab initioMP2/6-31+G(d,p)//HF/6-31+G(d,p) calculations, thestrengthof amide hydrogen bonding in the absence of steric hindrance isessentially independent of the angles defining thehydrogen bond.