Isolated and solvated chiroptical behavior in conformationally flexible butanamines
Isolated and solvated chiroptical behavior in conformationally flexible butanamines
复制标题
构象柔性丁胺中的分离和溶剂化手性光学行为
DOI：
10.1002/chir.23570
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发表时间：
2023
期刊：
影响因子：
2
通讯作者：
Vaccaro, Patrick H.
中科院分区：
文献类型：
--
作者：
Lemler, Paul M.;Craft, Clayton L.;Pollok, Corina H.;Regan, Thomas P.;Vaccaro, Patrick H.
在分离和溶剂化条件下研究了两种高柔性脂肪胺（2 R）-3-甲基-2-丁胺（R-MBA）和（2 R）-（3，3）-二甲基-2-丁胺（R-DMBA）的非共振光学活性，以考察构象异构的作用和外来扰动的影响.在六种溶剂中测量的旋光色散（ORD）在320-590 nm区域内呈现均匀的负旋光功率，随着周围环境的介电常数减小，手旋光响应的长波长幅度几乎单调增长。R-MBA [−11.031（98）和−2.29（11）]和R-DMBA [−9.434（72）和−1.350（48）]的环境气相样品在355和633 nm处提取的固有比旋度αλT（单位：deg dm−1[g/mL]−1），最好用高极性（但低极化率）的反直觉溶剂（如乙腈和甲醇）重现。试图定量解释观测到的光谱特征依赖于密度泛函理论（B3 LYP，cam-B3 LYP和色散校正类似物）和耦合簇理论（CCSD）的线性响应框架，并部署了可极化连续模型（PCM）的变体来解释隐式溶剂化的影响。在确定几个低位平衡几何形状的基础上（9个用于R-MBA，3个用于R-DMBA），系综平均的ORD曲线在T = 300 K时通过独立构象分析计算，这使得能够通过从相应的相对内能或自由能值导出的玻尔兹曼加权布居分数来组合针对每个异构体的优化结构预测的响应性质，后者来源于复合CBS‐APNO和G4分析。尽管对于分离的（气相）物质实现了理论和实验之间的合理雅阁，但溶液相结果不太令人满意，并且随着溶剂极性的增加而逐渐降解。这些趋势归因于溶剂介导的过渡态结构参数和能量指标的变化，这些过渡态分离和puperimentally隔离了由基础电子势能面支持的平衡构象，导致势垒位置的位移和/或势垒高度的降低，从而损害了独立构象的基本前提。
The nonresonant optical activity of two highly flexible aliphatic amines, (2R)‐3‐methyl‐2‐butanamine (R‐MBA) and (2R)‐(3,3)‐dimethyl‐2‐butanamine (R‐DMBA), has been probed under isolated and solvated conditions to examine the roles of conformational isomerism and to explore the influence of extrinsic perturbations. The optical rotatory dispersion (ORD) measured in six solvents presented uniformly negative rotatory powers over the 320–590 nm region, with the long‐wavelength magnitude of chiroptical response growing nearly monotonically as the dielectric constant of the surroundings diminished. The intrinsic specific optical rotation, αλT (in deg dm−1[g/mL]−1), extracted for ambient vapor‐phase samples ofR‐MBA [−11.031(98) and −2.29 (11)] andR‐DMBA [−9.434 (72) and −1.350 (48)] at 355 and 633 nm were best reproduced by counterintuitive solvents of high polarity (yet low polarizability) like acetonitrile and methanol. Attempts to interpret observed spectral signatures quantitatively relied on the linear‐response frameworks of density‐functional theory (B3LYP, cam‐B3LYP, and dispersion‐corrected analogs) and coupled‐cluster theory (CCSD), with variants of the polarizable continuum model (PCM) deployed to account for the effects of implicit solvation. Building on the identification of several low‐lying equilibrium geometries (nine forR‐MBA and three forR‐DMBA), ensemble‐averaged ORD profiles were calculated atT= 300 K by means of the independent‐conformer ansatz, which enabled response properties predicted for the optimized structure of each isomer to be combined through Boltzmann‐weighted population fractions derived from corresponding relative internal‐energy or free‐energy values, the latter of which stemmed from composite CBS‐APNO and G4 analyses. Although reasonable accord between theory and experiment was realized for the isolated (vapor‐phase) species, the solution‐phase results were less satisfactory and tended to degrade progressively as the solvent polarity increased. These trends were attributed to solvent‐mediated changes in structural parameters and energy metrics for the transition states that separate and putatively isolate the equilibrium conformations supported by the ground electronic potential‐energy surface, with the resulting displacement of barrier locations and/or decrease of barrier heights compromising the underlying premise of the independent‐conformer ansatz.