Zhang Huan-jun, Cheng Xue-rui, Ren Yu-fen, Zhu Xiang, Yuan Chao-sheng
Guang Pu Xue Yu Guang Pu Fen Xi. 2016 Feb;36(2):408-12.
Cyclobutanol (C₄H₈O) is one of the four-membered ring type molecules, which usually adopts a non-planar equilibrium conformation, and the substituent group OH can adopt two positions relative to the puckered ring, the axial or the equatorial, giving rise to an additional degree of freedom and various molecular conformations. Additionally, temperature is one important thermodynamic parameter that greatly influents the structure and induces the possibility of conformational change or crystal change. As a consequence, there may be a number of phase transitions and molecular conformations for cyclobutanol under different temperature. In this paper, Raman and infrared spectroscopic technique were applied to investigate the vibration modes of cyclobutanol. The results indicate that the main component of the liquid cyclobutanol is equatorial-trans (Eq-t) conformer with a few Eq-g conformers at ambient condition. Then differential scanning calorimetry (DSC) and low temperature Raman spectroscopic were applied to study the phase transition of cyclobutanol during the cooling and heating process. It is observed that the Raman spectra and the intensities of these bands are not significantly changed during the cooling process. The results indicate that there is sill no presence of solidification especially cooling to 140K, which indicates that the cyclobutanol still remains the liquid state and supercooled state is observed during the cooling process. And this supercooled liquid is one metastable state, not in thermodynamic equilibrium. Further cooling to 138 K, the super-cooling liquid cyclobutanol will transform into the glassy state, accompanied with a small change of entropy. During the heating process, as the temperature is raised to 180 K, the Raman peaks became sharper and some new characteristic peaks appeared abruptly and a discontinuous change was observed in bandwidths versus temperature. And these new signatures can be maintained upon to 220 K, and then will disappear as the temperature increasing continuously. This result indicates the one crystal phase transition and a melting transition present at around 180 and 220 K. In addition, it can be observed that the component of Eq-g conformer increases, accompanied with the crystallization during heating at around 180 K. These results were helpful to understand the kinetics of the crystallization process of other small organic molecules.
环丁醇（C₄H₈O）是一种四元环型分子，通常采用非平面平衡构象，取代基OH相对于褶皱环可处于两个位置，即轴向或赤道向，这产生了额外的自由度和各种分子构象。此外，温度是一个重要的热力学参数，它极大地影响结构并引发构象变化或晶体变化的可能性。因此，在不同温度下环丁醇可能存在多种相变和分子构象。本文应用拉曼光谱和红外光谱技术研究环丁醇的振动模式。结果表明，在环境条件下，液态环丁醇的主要成分是赤道 - 反式（Eq - t）构象体，还有少量的Eq - g构象体。然后应用差示扫描量热法（DSC）和低温拉曼光谱研究环丁醇在冷却和加热过程中的相变。观察到在冷却过程中拉曼光谱及其谱带强度没有明显变化。结果表明，尤其冷却到140K时仍未出现凝固现象，这表明环丁醇仍保持液态，在冷却过程中观察到过冷状态。这种过冷液体是一种亚稳态，并非处于热力学平衡状态。进一步冷却到138K时，过冷液态环丁醇将转变为玻璃态，同时伴随着熵的微小变化。在加热过程中，当温度升高到180K时，拉曼峰变得更尖锐，一些新的特征峰突然出现，并且在带宽与温度关系中观察到不连续变化。这些新特征在220K之前都能保持，然后随着温度持续升高而消失。该结果表明在180K左右出现一次晶相转变，在220K左右出现一次熔融转变。此外，可以观察到在180K左右加热过程中伴随着结晶，Eq - g构象体的成分增加。这些结果有助于理解其他小有机分子结晶过程的动力学。
