Microwave and Computational Study of Pivalic Sulfuric Anhydride and the Pivalic Acid Monomer: Mechanistic Insights into the RCOOH + SO 3 Reaction
Microwave and Computational Study of Pivalic Sulfuric Anhydride and the Pivalic Acid Monomer: Mechanistic Insights into the RCOOH + SO 3 Reaction
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新戊酸酐和新戊酸单体的微波和计算研究：RCOOH SO 3 反应的机理见解
DOI：
10.1021/acs.jpca.2c04904
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Leopold, Kenneth R.
中科院分区：
文献类型：
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作者：
Love, Nathan;Carpenter, Casey A.;Huff, Anna K.;Douglas, Christopher J.;Leopold, Kenneth R.
新戊酸酐 (CH3)3CCOOSO2OH (PivSA) 的微波光谱已通过旋转光谱法观察到。该化合物是通过 SO3 与 (CH3)3CCOOH（新戊酸）在超音速喷射中反应形成的，其方式类似于之前观察到的其他羧酸。计算分析表明，该反应最好描述为与叔丁基旋转 60° 相结合的周环过程。产品形成可以通过顺序（两步）或协调（一步）途径发生。前者涉及叔丁基通过 0.11 kcal/mol 势垒的内旋转，然后进行连接各部分的周环反应。后者经过一个二阶鞍点，其中内旋转和周环反应同时发生。这条路径在能量上是最有利的，因为鞍点结构的零点校正能量比假定的 (CH3)3CCOOH-SO3 前体复合物低 0.16 kcal/mol。报道了涉及一系列羧酸的额外计算工作，探讨了 RCOOH 反应物的气相酸度和碱度对反应能量的影响。这些计算以及先前对乙酸和三氟乙酸衍生物的实验和理论研究表明，羰基氧的碱性，而不是 COOH 质子的酸性，是该反应的重要驱动因素。作为标题分子实验工作的前身，记录了新戊酸单体母体和 OD 形式的微波光谱，并在此进行了报告。还描述了 SO3 的便捷合成。
The microwave spectrum of pivalic sulfuric anhydride, (CH3)3CCOOSO2OH (PivSA), has been observed by rotational spectroscopy. The compound was formed by the reaction of SO3with (CH3)3CCOOH (pivalic acid) in a supersonic jet in a manner analogous to that previously observed with other carboxylic acids. Computational analysis indicates that the reaction is best described as a pericyclic process coupled with a 60° rotation of thet-butyl group. Product formation can occur through either a sequential (two-step) or a concerted (one-step) pathway. The former involves an internal rotation of thet-butyl group through a 0.11 kcal/mol barrier followed by the pericyclic reaction that joins the moieties. The latter passes through a second-order saddle point in which the internal rotation and pericyclic reaction occur simultaneously. This path is the most energetically favorable, as the zero-point corrected energy at the saddle point structure is 0.16 kcal/mol below that of a putative (CH3)3CCOOH–SO3precursor complex. Additional computational work involving a series of carboxylic acids is reported, which explores the effects of gas-phase acidity and basicity of the RCOOH reactant on reaction energetics. These calculations, together with prior experimental and theoretical studies of the acetic and trifluoroacetic derivatives, demonstrate that the basicity of the carbonyl oxygen, not the acidity of the COOH proton, is the important driving factor for the reaction. As a precursor to the experimental work on the title molecule, microwave spectra of the parent and OD forms of the pivalic acid monomer were recorded and are reported here as well. A convenient synthesis of SO3is also described.