We discovered a new structure II (sII) hydrate forming agent, allyl alcohol (AA), in the presence of methane (CH4) for the first time, and characterized the crystal structure, guest distribution, and phase equilibria of the (AA+CH4) hydrate. Using solid-state 13C NMR and Raman spectroscopy, the crystal structure of the (AA+CH4) hydrate was confirmed to be a sII hydrate, and the CH4 molecule was found to be encapsulated in both the large and small cages of the sII hydrate. In addition, AA was found to be included in the large cages of the sII hydrate in the Gauche-Gauche form based on the measured- and calculated-NMR spectra. Notably, we investigated the free OH signal of AA in the Raman spectra to determine whether hydrogen bonding occurred between host and guest molecules; however, we could not determine whether the existence of the free OH signal was consistent with this host-guest interaction. To clearly identify the crystal structure and possible host-guest interactions, a high-resolution powder X-ray diffraction (HRPD) pattern of our (AA+CH4) hydrate sample was analyzed using Rietveld analysis with the direct space method. The crystal structure of the (AA+CH4) hydrate was assigned as the cubic Fd3m structure with a lattice constant of 17.1455 Å. In particular, the shortest distance between the AA molecule in the hydrate cages and an oxygen atom in the host water was estimated to be 2.55 Å; thus, we concluded that the hydroxyl group of the AA molecule was hydrogen-bonded to the host water framework. Finally, we measured the phase equilibrium conditions of the binary (AA+CH4) hydrate and found that the equilibrium pressure conditions of the binary (AA+CH4) hydrate were slightly higher than those of the pure CH4 hydrate.

中文翻译：

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烯丙醇和 CH4 形成天然气水合物：光谱和热力学分析

我们首次在甲烷 (CH4) 存在下发现了一种新的结构 II (sII) 水合物形成剂烯丙醇 (AA)，并表征了 (AA+CH4) 的晶体结构、客体分布和相平衡) 水合物。使用固态 13C NMR 和拉曼光谱，(AA+CH4) 水合物的晶体结构被证实为 sII 水合物，并且发现 CH4 分子被包裹在 sII 水合物的大笼和小笼中。此外，根据测量和计算的 NMR 光谱，发现 AA 包含在 Gauche-Gauche 形式的 sII 水合物的大笼中。值得注意的是，我们在拉曼光谱中研究了 AA 的游离 OH 信号，以确定主客体分子之间是否发生氢键；然而，我们无法确定游离 OH 信号的存在是否与这种主客交互一致。为了清楚地确定晶体结构和可能的主客体相互作用，我们使用 Rietveld 分析和直接空间法分析了我们的 (AA+CH4) 水合物样品的高分辨率粉末 X 射线衍射 (HRPD) 图案。(AA+CH4) 水合物的晶体结构被指定为立方 Fd3m 结构，晶格常数为 17.1455 Å。特别是，水合物笼中的 AA 分子与主体水中的氧原子之间的最短距离估计为 2.55 Å；因此，我们得出结论，AA 分子的羟基与主体水骨架形成氢键。最后，