Racemization barriers of helicenes: A computational study
Racemization barriers of helicenes: A computational study
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DOI：
10.1021/ja950774t
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发表时间：
1996-06-26
影响因子：
15
通讯作者：
Borkent, JH
中科院分区：
文献类型：
--
作者：
Janke, RH;Haufe, G;Borkent, JH
用AM1、MNDO和PM3计算了五螺旋烯对非螺旋烯的外消旋势垒。所有方法得到的C-s过渡态的能量都低于C-2v对称态。AM1计算的载流子与实验值最吻合。结果的可靠性通过从头算方法得到了证实，该方法使用了在GAUSSIAN94包中实现的具有3-21G基集的B3LYP泛函。此外，还用AM1方法计算了12个甲基取代螺旋烯。1-甲基取代的五螺旋烯和六螺旋烯的外消旋势垒至少与次之的未取代螺旋烯一样高。1‘位的第二个甲基进一步增加了势垒，而2 ’位的甲基对外消旋势垒没有严重的影响。
The racemization barriers of pentahelicene up tp nonahelicene have been computed with AM1, MNDO, and PM3. All methods lead to C-s transition states which have lower energy than those with C-2v symmetry. The carriers calculated by AM1 match the experimental values best for all helicenes. The reliability of the results has been confirmed by ab initio methods using the B3LYP functional with the 3-21G basis set as implemented in the GAUSSIAN94 package. Furthermore, 12 methyl-substituted helicenes have been computed with the AM1 method. The racemization barriers of 1-methyl-substituted penta- and hexahelicene are at least as high as that of the next higher unsubstituted helicene. A second methyl group in the 1'-position increases the barrier further, while methyl groups in the 2-position do not have a severe influence on the racemization barrier.