New molecular devices: In search of a molecular ratchet

被引:149
作者
Kelly, TR [1 ]
Sestelo, JP [1 ]
Tellitu, I [1 ]
机构
[1] Boston Coll, Dept Chem, EF Merkert Chem Ctr, Chestnut Hill, MA 02167 USA
关键词
D O I
10.1021/jo9723218
中图分类号
O62 [有机化学];
学科分类号
070303 ; 081704 ;
摘要
The triptycene-substituted [3]- and [4]helicenes 1 and 2 were examined as possible molecular versions of mechanical ratchets, where the triptycene serves as the ratchet wheel and the helicenes as pawl and spring. The syntheses of 1 and 2b are described. H-1 NMR was employed to examine rotation around the triptycene/helicene single bond; at 20 degrees C rotation is frozen for both 1 and 2b, but the NMR of 1 revealed a plane of symmetry, indicating that 1 cannot function as a unidirectional ratchet. In contrast, NMR revealed that, like a ratchet, triptycyl[4]helicene 2b lacks the symmetry of 1 and has a barrier to rotation of 24.5 kcal/mol, but spin polarization transfer NMR experiments indicated the triptycene in 2b nonetheless rotates equally in both directions. That outcome is rationalized from the standpoint of thermodynamics.
引用
收藏
页码:3655 / 3665
页数:11
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