摘要
Density functional theory (DFT) has been used to determine the equilibrium geometries, IR, total energies and NMR chemical shifts of various kinds of lactides. According to the calculations, besides L-lactide and D-lactide, three kinds of meso-lactides have been obtained: meso-i-lactide, meso-alpha-lactide and meso-beta-lactide. The latter two are enantiomers. It indicates that meso-i-lactide with a symmetrical center is a transition state connecting meso-alpha-lactide and meso-p-lactide, with activation energy only about 6.77 U/mol. It is assumed that meso-lactide prepared by previous experiments may be a racemate of meso-a-lactide and meso-beta-lactide. The energy of L(or D)-lactide is predicted to be about 4.83 kJ/mol lower than meso-alpha(or beta)-lactide. Time-dependent DFT calculations show that the strongest absorption peaks Of L(or D)-lactide and tneso-alpha(or beta)-lactide are at about 155 and 158 nm, respectively.
- 出版日期2007-8-20
- 单位河南大学