[3]cumulenes (buta‐1,2,3‐trienes) were synthesized by developed procedures. The activation barriers to rotation ΔG≠ were measured by variable temperature NMR spectroscopy and found to be as low as 11.8 kcal mol−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 Å as measured
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)。旋转的激活壁垒ΔG ≠通过可变温度NMR光谱法测量,发现低至11.8 kcal mol -1在围绕位阻单键旋转的障碍范围内。通过X射线晶体学测定,推挽取代的[3]
异丙苯部分的中央CC键缩短到1.22Å,导致键长交替(B
LA)高达0.17Å。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额外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。