Density functional study of 4-pyrone and 2-pyrone

Density functional (B3LYP) calculations using 6-31G* have been made to estimate the bond lengths and angles for 4-pyrone and 2-pyrone. The predicted bond lengths and angles for 4-pyrone are in excellent agreement with experimental results. However for 2-pyrone, two bond angles are in very poor agreement with the experimental results. Results of MP2 calculations are in good agreement with B3LYP results. Here again the two bond angles for 2-pyrone are very poorly predicted. To confirm this the calculations have been repeated with much larger 6-311+G (d,p) basis set. This again does not change our conclusion. The calculated dipole moments and C-13 NMR chemical shifts for 4-pyrone and 2-pyrone are in good agreement with experimental results.