| Popis: |
The proton chemical shifts for 29 methoxy, dimethylamino and methylthio substituted polycylic aromatics are reported. A strong deshielding effect on α-protons due to peri substitution is always found. This effect appears to increase in going from the nitrogen to the oxygen derivatives and is largest for the sulfur compounds. In 9,10-bis-(methylthio)anthracene where the S-Me is constrained to lie out of the plane of the rings, the peri effect is largest. A combination of charge distribution, ring current and peri effects reproduces the measured aromatic proton chemical shifts with reasonable accuracy. |
