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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Conformational Studies of an N-Acylated Hindered Amine Light Stabilizer
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Conformational Studies of an N-Acylated Hindered Amine Light Stabilizer

机译：N-酰化受阻胺光稳定剂的构象研究

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摘要

The low-energy conformations of a commercial, N-acylated, hindered amine light stabilizer, Tinuvin 440, are examined both theoretically and experimentally. Candidate structures are determined from an empirical force-field search algorithm and re-optimized using a variety of semiempirical and first-principles quantum chemical methods. The global minimum is robustly predicted to have a twist-boat configuration with the substituted N in its six-membered heterocycle not one of the "flagpole" substituents. First-principles Hartree-Fock, post-Hartree-Fock, and density functional theory calculations agree well on the relative stabilities of different conformers, while force-field and semiempirical methods prove unreliable. The present study disagrees with earlier semiempirical results and contradicts their implication that the oxidation and photostabilization behavior of Tinuvin 440 are strongly influenced by a trans-annular, intramolecular hydrogen bond. An alternative boat conformation containing such a bond is predicted by first-principles methods to lie at least 3.4 kcal/mol above the global minimum. NMR and IR spectral data confirm that intramolecular hydrogen bonding plays a negligible role at room temperature and are consistent with the theoretically predicted ground state.
机译：在理论上和实验上都对商用N-酰化受阻胺光稳定剂Tinuvin 440的低能构象进行了研究。候选结构是根据经验力场搜索算法确定的，并使用多种半经验和第一原理量子化学方法进行了重新优化。强有力地预测了该全局最小值具有双态，其六元杂环中具有取代的N而不是“旗杆”取代基之一。第一性原理Hartree-Fock，后Hartree-Fock和密度泛函理论计算在不同构象异构体的相对稳定性上非常吻合，而力场和半经验方法证明是不可靠的。本研究与较早的半经验结果不同，并且与它们的含义相反，即Tinuvin 440的氧化和光稳定行为受到跨环分子内氢键的强烈影响。通过第一性原理方法预测，包含这种键的另一种舟形结构至少比整体最小值高3.4 kcal / mol。 NMR和IR光谱数据证实分子内氢键在室温下起的作用可忽略不计，并且与理论上预测的基态一致。

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