Conformational analysis of alkylated biuret and triuret: evidence for helicity and helical inversion in oligoisocyanates
Conformational analysis of alkylated biuret and triuret: evidence for helicity and helical inversion in oligoisocyanates
复制标题
烷基化缩二脲和三缩脲的构象分析：低聚异氰酸酯中螺旋性和螺旋反转的证据
作者：
Roth;O’Leary;Wade;Miller;Armstrong;Thoburn
利用核磁共振技术研究了几种低聚异氰酸酯的构象，以研究多异氰酸酯中螺旋的发生和动力学。五乙基二脲和六乙基三脲在溶液中呈螺旋状。对于六乙基三脲，存在对称和不对称螺旋。不仅观察到这些形式的相互转换(DeltaG(SA)（双匕首）= 9.3 +/- 0.4 kcal/mol)，而且还观察到螺旋度的反转(DeltaG（PM)（双匕首）= 9.0 +/- 0.4 kcal/mol）。后一过程的合并模式为一致的、控制的螺旋反转提供了直接证据。
The conformations of several oligoisocyanates have been investigated by NMR in order to study the onset and dynamics of helicity in polyisocyanates. Pentaethylbiuret and hexaethyltriuret were found to adopt turns and helices in solution. For hexaethyltriuret, symmetric and asymmetric helices are present. Not only is an interconversion of these forms observed (DeltaG(SA)(double dagger) = 9.3 +/- 0.4 kcal/mol) but also a reversal of helicity (DeltaG(PM)(double dagger) = 9.0 +/- 0.4 kcal/mol). The coalescence pattern for the latter process provides direct evidence for a concerted, conrotatory helical inversion.