A quantum-mechanical study on the stereochemistry of the isomeric bipyrroles, bifurans, bithiophenes, thienylfurans and biselenophenes

✍ Scribed by V. Galasso; N. Trinajstić

• Book ID: 104204543
• Publisher: Elsevier Science
• Year: 1972
• Tongue: French
• Weight: 656 KB
• Volume: 28
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(01)88965-1

✦ Synopsis

most probable conformational arrangements of isomeric bipyrroks, bifurans, bithiophenes, thienylfurans, and biselenophenes have been investigated using the Extended Hflckel MO approach. The barrier heights between the syn and anti forms decrease sharply on going along the series bifurans bithiophene$ and biselenophenes. The barrier height for the interconversion syn w unti follows the trend : 2.J z 23' > 3,3'. The energy difference between the syn and wrti conformers is small (except in the case of 2,2'-bifuran). Planar syn conformation is predicted more stabk than unri for 2,2'-and 2,3'-isomers (except for 2,3'-biselenophene), while the 3,3'-isomers are predicted to have anti conformation more stable than syn. The tendency to assume a nonplanar conformation at the equilibrium is shown by l,l'-bipyrrole, 2,3'-biselenophene, 3,3'-bithiophene and 3.3'-biselenophene For the two energetically most favourabk conformations of each molecule the charge distribution is calculated using the CNDO/2 method.