- 作者: 賴怡興
- 作者服務機構: Dept. of Chemistry, National Univ. of Singapore, Kent Ridge, Republic of Singapore
- 中文摘要: Annelation or substitution of the (1,4)-bridged ring of [ 2/sub 2/ ] (1,3)(1,4)cyclophane (4), such as in (8) and (9), respectively, result in two different conformational ground states in each case. Each conformational ground state involves a different destabilizing factor arising from one form of non-bonding interaction. Only the conformers (8b) and (9b) were isolated experimentally. Their corresponding precursors (11) and (23) were also found to be conformationally rigid. Only the conformers (11a) and (23a) were isolated indicating an abrupt change in conformational preference going from the dithia [ 3/sub 2/ ] cyclophanes to the respective [ 2/sub 2/ ] cyclophanes. The selectively methylated [ 2/sub 2/ ] cyclophanes (27), (31 ) and (32) were, however, found to be conformationally mobile. There is an increase of about 10-15kJ/mol in conformational energy barrier going from (4) to (27) or (31). This is consistent with the fact that the presence of the methyl substituents increases the relative conformational ground-state energy more than it would affect the transition-state energy. The conformational barrier of (32) was unexpectedly found to be similar to those of (27) and (31). This could be explained by a decrease in the transition-state energy due to an inward bending of the (1,4)-bridged ring accompanied by a decrease in conformational ground-state energy due to an outward bending of the methyl groups in (32).
- 英文摘要: --
- 中文關鍵字: Cyclophane; Conformational Behavior; Non-Bonding Interaction; Conformational Ground State; Conformational Energy Barrier
- 英文關鍵字: 構形行為;非鍵結交互作用;構形基態;構形位能井