Department of Chemistry, Graduate School of Science , Hiroshima University , 1-3-1 Kagamiyama , Higashi-Hiroshima 739-8526 , Japan.
J Org Chem. 2019 Nov 1;84(21):13483-13489. doi: 10.1021/acs.joc.9b01730. Epub 2019 Sep 6.
X-ray crystallography of an acetoxy-protected bisresorcinarene and biscavitands possessing phosphonate and dialkylsilyl bridges revealed that the bisresorcinarene and the biscavitands adopt helical forms in the solid state. Helical conformations were also found in solution. The helix-helix interconversions of the biscavitands occurred with high activation barriers of more than 50 kJ mol. The activation parameters of the helix-helix interconversions were determined using exchange spectroscopy (EXSY). The positive activation enthalpies and the negative activation entropies suggest that the transition states of the helix-helix interconversion process are most likely more strained and symmetric than the ground states. The compensatory enthalpy-entropy correlation is found in the series of activation parameters, giving rise to a compensation temperature of 254 K.
X 射线晶体学研究表明，一种带有乙酰氧基保护基的双杯芳烃和双杯吡咯烷同时具有膦酸酯和二烷基硅桥，在固态中采用螺旋形式。在溶液中也发现了螺旋构象。双杯吡咯烷的螺旋-螺旋互变伴随着超过 50 kJ mol 的高活化能垒。使用交换光谱（EXSY）确定了双杯吡咯烷的螺旋-螺旋互变的活化参数。正的活化焓和负的活化熵表明，螺旋-螺旋互变过程的过渡态比基态更紧张和对称。在一系列活化参数中发现了补偿焓熵相关性，导致补偿温度为 254 K。
