(1R(*),2S(*),5R(*))-5-tert-Butyl-2-hydroxycyclopentanecarboxylic acid exists in several solid phases, two of which are investigated in this report: a first phase (phase I) obtained by crystallization from common solvents and a second phase (phase II) obtained by heating the first phase above ca. 70 degrees C. The second phase appears to be the stable phase at ambient temperature, and the first phase appears to be a metastable phase. A third phase (phase III), which reverts to phase II on standing at room temperature, is obtained by cooling the melt to room temperature. The rates of rotation of the tert-butyl groups in phases I and II have been measured by CP/MAS NMR techniques. The activation parameters for the tert-butyl group rotation differ markedly between the two phases: phase I, Delta H not equal = 59.0 +/- 2.1 kJ mol(-1), Delta S not equal = 51.6 +/- 8.1 J K-1 mol(-1); and phase II, Delta H not equal = 43.9 +/- 2.5 kJ mol(-1), Delta S not equal = 28.3 +/- 9.3 J K-1 mol(-1). The structure of phase I has been solved by X-ray diffraction techniques, and this assists in understanding the experimental observations.
(1R(*),2S(*),5R(*))-5-叔丁基-2-羟基
环戊烷羧酸存在几种固体相态,其中两种在本报告中进行了研究:第一相(相I)通过从普通溶剂中结晶获得,而第二相(相II)则通过将第一相加热至约70摄氏度以上获得。第二相似乎是环境温度下的稳定相,而第一相则似乎是亚稳态。将熔体冷却至室温会得到第三相(相III),但该相在室温下会逐渐转变为相II。通过CP/MAS NMR技术测定了相I和相II中叔丁基基团的旋转速率。两个相中的叔丁基基团旋转活化参数有显著差异:相I,ΔH≠59.0 ± 2.1 kJ/mol,ΔS≠51.6 ± 8.1 J·K⁻¹·mol⁻¹;相II,ΔH≠43.9 ± 2.5 kJ/mol,ΔS≠28.3 ± 9.3 J·K⁻¹·mol⁻¹。相I的结构已通过X射线衍射技术解决,这有助于理解实验结果。