G. Buemi
Apr 15, 1989
Citations
0
Influential Citations
14
Citations
Journal
Bulletin of the Chemical Society of Japan
Abstract
AM1 and MNDO methods have been used for optimizing the molecular geometry of all the possible conformations of thieno[3,4-b]thiophene-2-carboxylic acid (1), of its methyl ester (2) and of acetic thieno[3,4-b]thiophene-2-carboxylic anhydride (3). Both methods give comparable results for the thieno[3,4-b]thiophene framework but rather different bond angles for the substituent group of 3. In any case, an equilibrium between two (1,2) or more (3) conformations is conceivable. Although the most stable conformations are predicted to be planar, the rotation of the substituent group implies only low energy increase (rotation barriers are calculated to be about 2 kcal mol−1) which allows wide oscillations. The π→π* electronic transitions do not differ appreciably from those of the parent thieno[3,4-b]thiophene molecule and are better accounted for by the conformations having remarkable rotation around the C7–C9 bond.