Theoretical study of weak intermolecular and intramolecular interactions


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CH/n (CH/O, CH/X) 水素結合による解釈

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Theoretical study of weak intermolecular and intramolecular interactions

  1. 1. アノマー効果再訪 CH/ n (CH/O, CH/X) 水素結合による解釈 高橋 修,山崎勝義(広大) 河野雄次,上田一義(横国大) 末澤裕子(文科省),西尾元宏( CHPI 研)
  2. 2. Anomeric effect of glucosides
  3. 3. Anomeric effect of six-member heterocyclic compounds X, Y = O, S; Z = O, halogens, etc.
  4. 4. Generalized anomeric effect
  5. 5. Theory of the anomeric effect <ul><li>The equatorial conformation is unstable due to the dipolar interaction (well explains the solvent effect ). </li></ul><ul><li>(2) The axial conformation is stabilized by the donation of lone pair electrons to the  * orbital of the C-X bond ( shortening of the CH 2 -O bond in gauche or axial conformers) </li></ul><ul><li>  Radom, Hehre, Pople, J. Am. Chem. Soc . 1971 , 93 , 289 </li></ul>
  6. 6. Our hypothesis <ul><li>The CH/ n ( CH/O, CH/halogen , etc.) hydrogen bond is important </li></ul>
  7. 7. Computational method <ul><li>MP2/6-311++G(d,p)//MP2/6-31G(d) </li></ul><ul><li>Vibrational frequencies were calculated using the analytical second derivatives at the same level of the geometry optimization for each conformer. </li></ul><ul><li>Using these results, the thermal energy corrections were added to the total Gibbs energy at 298.15 K and 1 atmosphere of pressure. </li></ul><ul><li>NBO: B3LYP/3-21G* by NBO 3.1 program </li></ul><ul><li>13 C chemical shifts: B3LYP/6-31G*//B3LYP/6-311++G** relative to TMS </li></ul>
  8. 8. Difference in the Gibbs energy between ax and eq conformers G eq – G ax (  G eq-ax ) of 2-substituted oxanes 1 and 1,3-dioxanes 2
  9. 9. Bond lengths d O -C 2 and d C 2 - Z in 1
  10. 10. Bond lengths d O-C 2 and d C 2 -O and  d ax-eq in 2-methoxy oxane, glucose and glycosides
  11. 11. Non-bond distances between axial hydrogens H 4ax and H 6ax vs. Z, calculated for 2-substituted oxanes
  12. 12. Conformation of simple aliphatic molecules (5-member CH/O hydrogen bond)
  13. 13. NBO charges of the axial and equatorial conformers of in 2-methoxy oxane
  14. 14. Differences in the NBO charges between the axial and equatorial conformers of the relevant atoms in 2-substituted oxanes
  15. 15. Calculated 13 C NMR chemical shifts and the difference between the axial and equatorial conformers for C 4 and C 6 in 2-substituted oxanes (  -effect )
  16. 16. CH/O 水素結合による解釈 Eliel, J. Org. Chem . 1968 , 33 , 3754
  17. 17.  -Anomers of glycosides Lichtenthaler, Liebig Ann. Chem. 1990 , 1001
  18. 18.  -Anomers of glycosides Horton, J. Org. Chem . 1965 , 30 , 3387
  19. 19. Conclusions <ul><li>Ab initio MO calculations have revealed that the Gibbs energy of the axial conformer in 1 and 2 is smaller than that of the corresponding equatorial conformer, when Z is an electron-withdrawing group. </li></ul><ul><li>The non-bonded distance between the 2-substituent and an axial C-H has been shown shorter than the van der Waals distance , suggesting the importance of 5-member CH/ n hydrogen bonds. </li></ul><ul><li>Analysis of the natural bonding orbital (NBO) charge of the relevant protons and carbons have revealed an appreciable difference between the conformers: more positive for H and more negative for C in the axial conformer than in the corresponding equatorial conformer. </li></ul><ul><li>The CH/ n (CH/O, CH/X) hydrogen bond has been suggested to be an important factor in stabilizing the axial conformations of these compounds. This mechanism is compatible with the solvent effect . </li></ul>