Kim J H, Hubig S M, Lindeman S V, Kochi J K
Department of Chemistry, University of Houston, Houston, Texas 77204-5641, USA.
J Am Chem Soc. 2001 Jan 10;123(1):87-95. doi: 10.1021/ja001939n.
The solid-state [4+2] cycloaddition of anthracene to bis(N-ethylimino)-1,4-dithiin occurs via a unique single-phase topochemical reaction in the intermolecular (1:1) charge-transfer crystal. The thermal heteromolecular solid-state condensation involves the entire crystal, and this rare crystalline event follows topochemical control during the entire cycloaddition. As a result, a new crystalline modification of the Diels-Alder product is formed with a crystal-packing similar to that of the starting charge-transfer crystal but very different from that of the (thermodynamically favored) product modification obtained from solution-phase crystallization. Such a single-phase transformation is readily monitored by X-ray crystallography at various conversion stages, and the temporal changes in crystallographic parameters are correlated with temperature-dependent (solid-state) kinetic data that are obtained by 1H NMR spectroscopy at various reaction times. Thus, an acceleration of the solid-state reaction over time is found which results from a progressive lowering of the activation barrier for cycloaddition in a single crystal as it slowly and homogeneously converts from the reactant to the product lattice.
蒽与双（N - 乙基亚氨基）-1,4 - 二硫因的固态[4 + 2]环加成反应是通过分子间（1:1）电荷转移晶体中的独特单相拓扑化学反应发生的。热异分子固态缩合涉及整个晶体，并且这种罕见的晶体事件在整个环加成过程中遵循拓扑化学控制。结果，形成了一种新的狄尔斯 - 阿尔德产物的晶体变体，其晶体堆积类似于起始电荷转移晶体，但与从溶液相结晶获得的（热力学有利的）产物变体非常不同。通过X射线晶体学在各个转化阶段很容易监测这种单相转变，并且晶体学参数的时间变化与通过1H NMR光谱在不同反应时间获得的温度依赖性（固态）动力学数据相关。因此，发现固态反应随时间加速，这是由于单晶中环加成的活化能垒随着它从反应物晶格缓慢且均匀地转变为产物晶格而逐渐降低所致。
