The crystal structure of 3,5-bistrifluoromethylhydrocinnamic acid [systematic name: 3-[3,5-bis(trifluoromethyl)phenyl]propanoic acid], C11H8F6O2, has been determined and described. The structure was subject to the Hirshfeld surface-analysis and CE-B3LYP interaction-energies calculations. The title compound crystallises in the monoclinic P21/c space group with one molecule in the asymmetric unit. The propanoic acid side chain of the studied molecule has a bent conformation. The key supramolecular motif in the crystal structure is a centrosymmetric O–H∙∙∙O hydrogen-bonded dimer (R22(8) in the graph set notation). According to CE-B3LYP, the molecules involved in this motif exhibit the strongest pairwise interaction total energy (Etot = −67.9 kJ/mol). On the other hand, there are seven other interacting molecular pairs with significant Etot values in the range of −17 to −28 kJ/mol. In these, the energy is dominated by the dispersive contribution. A survey of the Cambridge Structural Database revealed that in other 3-phenylpropanoic acid structures, the middle dihedral angle of the propanoic acid side chain is always in the trans conformation. This contrasts the current structure where this dihedral angle is in the gauche conformation. According to the Density Functional Theory calculations in the gas phase (at the B3LYP/aug-cc-pvDZ level), the presence of the two CF3 groups (strong electron-withdrawing character) increases the population of the gauche conformers by a substituent electronic effect, and this may be a minor factor contributing to the appearance of this conformation observed in the solid state.

中文翻译：

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3,5-双三氟甲基氢化肉桂酸的结构分析

3,5-双三氟甲基氢化肉桂酸[系统名称：3-[3,5-双(三氟甲基)苯基]丙酸]，C11H8F6O2的晶体结构已被测定和描述。该结构经过 Hirshfeld 表面分析和 CE-B3LYP 相互作用能计算。标题化合物在单斜晶系 P21/c 空间群中结晶，不对称单元中有一个分子。所研究分子的丙酸侧链具有弯曲构象。晶体结构中的关键超分子基序是中心对称的 O–H∙∙∙O 氢键二聚体（图形集符号中的 R22(8)）。根据CE-B3LYP，参与该基序的分子表现出最强的成对相互作用总能量（Etot = -67.9 kJ/mol）。另一方面，还有其他七个相互作用的分子对，其显着的 Etot 值在 -17 至 -28 kJ/mol 范围内。其中，能量以色散贡献为主。剑桥结构数据库的调查显示，在其他3-苯基丙酸结构中，丙酸侧链的中间二面角始终处于反式构象。这与当前的结构形成对比，其中该二面角处于左构象中。根据气相密度泛函理论计算（在 B3LYP/aug-cc-pvDZ 水平），两个 CF3 基团（强吸电子特性）的存在通过取代基电子效应增加了 gauche 构象异构体的数量，这可能是导致在固态中观察到的这种构象出现的一个次要因素。