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首页> 外文期刊>Chemistry: A European journal >Push-Pull Buta-1,2,3-trienes: Exceptionally Low Rotational Barriers of Cumulenic C=C Bonds and Proacetylenic Reactivity
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Push-Pull Buta-1,2,3-trienes: Exceptionally Low Rotational Barriers of Cumulenic C=C Bonds and Proacetylenic Reactivity

机译：推挽式Buta-1,2,3-三烯：极低的Cumulenic C = C键旋转屏障和原炔反应性

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摘要

A variety of asymmetrically donor-acceptor-substituted [3]cumulenes (buta-1,2,3-trienes) were synthesized by developed procedures. The activation barriers to rotation G were measured by variable temperature NMR spectroscopy and found to be as low as 11.8kcalmol(-1), in the range of the barriers for rotation around sterically hindered single bonds. The central CC bond of the push-pull-substituted [3]cumulene moiety is shortened down to 1.22 angstrom as measured by X-ray crystallography, leading to a substantial bond length alternation (BLA) of up to 0.17 angstrom. All the experimental results are supported by DFT calculations. Zwitterionic transition states (TS) of bond rotation confirm the postulated proacetylenic character of donor-acceptor [3]cumulenes. Additional support for the proacetylenic character of these chromophores is provided by their reaction with tetracyanoethene (TCNE) in a cycloaddition-retroelectrocyclization (CA-RE) cascade characteristic of donor-polarized acetylenes.
机译：通过开发的方法合成了多种不对称的供体-受体取代的[3]枯烯（丁二烯，1,2,3-三烯）。旋转G的激活壁垒是通过可变温度NMR光谱测量的，发现在绕位阻单键旋转的壁垒范围内低至11.8kcalmol（-1）。通过X射线晶体学测定，推挽取代的[3]枯烯部分的中央CC键缩短至1.22埃，导致高达0.17埃的实质键长交替（BLA）。 DFT计算支持所有实验结果。键旋转的两性离子跃迁状态（TS）证实了供体-受体[3] cumulenes的假定的炔炔原特性。这些生色团的原炔性质的其他支持是通过它们与供体极化的乙炔的环加成-逆电环化（CA-RE）级联反应中的四氰基乙烯（TCNE）反应提供的。

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