The structures of partially self-included forms of para-alkanoyl calix[4]arenes, with different lengths of acyl chain (C4âC16), were compared using X-ray diffraction data. The carbonyl group in the calix[4]arenes fixes the position of the two first carbon atoms in the plane of the phenyl ring and effectively expands the cavity. The accessibility of the cavity to small molecules strongly depends on the length of alkanoyl arm. For short arms (C4âC8), the hostâhost van der Waals interactions are not strong enough and enable easy access by potential guests to the cavity. Long alkanoyl arms compensate the directing effect of the carbonyl group and close the cavity to potential guests. A comparison of para-alkanoyl calix[4]arene with para-alkyl examples allows one to estimate the chain lengths that will enable easy inclusion of potential guests. It was found that the former should be ca. 1.5 times longer than the length of the rigid calixarene fragment.
使用X射线衍射数据比较了具有不同酰基链长度(C4-C16)的半烷酰杯[4]
芳烃的部分自包含形式的结构。杯[4]
芳烃中的羰基固定了苯环平面中前两个碳原子的位置,并有效地扩大了空腔。小分子进入空腔的能力在很大程度上取决于烷酰臂的长度。对于短臂(C4-C8),主-主范德华相互作用不够强,潜在客体可以轻松进入空腔。长烷酰臂可以补偿羰基的定向作用,并使潜在客体无法进入空腔。通过比较半烷酰杯[4]
芳烃和半烷基示例,可以估算出易于容纳潜在客体的链长。研究发现,前者的长度应比刚性杯
芳烃片段的长度长1.5倍左右。