Zheng Chu, Mao Yuezhi, Markland Thomas E, Boxer Steven G
Department of Chemistry, Stanford University, Stanford, California 94305, United States.
Department of Chemistry and Biochemistry, San Diego State University, San Diego, California 92182, United States.
J Am Chem Soc. 2025 Feb 19;147(7):6227-6235. doi: 10.1021/jacs.4c18102. Epub 2025 Feb 10.
C-H···O hydrogen bonds are formed in systems ranging from biomolecular complexes to small-molecule structures. Previous work has focused on the blueshifts in the C-H stretching frequency () induced by these hydrogen bonds and their chemical and biological roles. Here, we show that, in contrast, terminal alkyne C-H hydrogen bonds exhibit large redshifts (50-100 cm) upon hydrogen bonding with oxygen-containing solvents. Using spectroscopic and computational approaches, we elucidate and compare the roles of the vibrational Stark effect, bond polarization, and charge transfer in driving the C-H redshift. We show that the redshifts of alkyne's terminal C-H upon the formation of hydrogen bonds correlate with the Lewis basicity of the solvent and are significantly larger than those arising solely from solvent electric fields (vibrational Stark effect), differing from the well-studied redshift of carbonyl vibrations induced by hydrogen bonds. Through a decomposition of vibrational frequency shifts based on DFT calculations using absolutely localized molecular orbitals, we demonstrate that including the effects of bond polarization and charge transfer, in addition to the vibrational Stark effect, results in quantitative agreement between experimentally observed C-H frequency shifts and the theoretically predicted values in various oxygen-containing solvents. Our results highlight the significance of effects beyond pure electrostatics in accounting for the large redshifts in C-H···O hydrogen bonds and exemplify our approach to quantifying the contributions from different physical effects.
从生物分子复合物到小分子结构的系统中都会形成C-H···O氢键。此前的研究工作主要集中在这些氢键所引起的C-H伸缩频率（）蓝移及其化学和生物学作用上。相比之下，本文我们发现，末端炔烃C-H氢键在与含氧溶剂形成氢键时会出现大幅红移（50 - 100厘米）。我们采用光谱学和计算方法，阐明并比较了振动斯塔克效应、键极化和电荷转移在驱动C-H红移中的作用。我们表明，炔烃末端C-H在形成氢键时的红移与溶剂的路易斯碱性相关，且显著大于仅由溶剂电场引起的红移（振动斯塔克效应），这与研究充分的氢键诱导的羰基振动红移不同。通过基于使用绝对定域分子轨道的密度泛函理论计算对振动频率位移进行分解，我们证明，除了振动斯塔克效应外，纳入键极化和电荷转移的影响，会使实验观测到的C-H频率位移与各种含氧溶剂中的理论预测值之间达成定量一致。我们的结果突出了纯静电效应之外的其他效应在解释C-H···O氢键大幅红移中的重要性，并例证了我们量化不同物理效应贡献的方法。
