A theoretical analysis of enantiomerization in aromatic amides
A theoretical analysis of enantiomerization in aromatic amides
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DOI：
10.1021/jp013127z
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发表时间：
2002-03-21
影响因子：
2.9
通讯作者：
Sordo, TL
中科院分区：
文献类型：
--
作者：
Campomanes, P;Menéndez, MI;Sordo, TL
在MP2-FC/6-311+G（d，p）//B3 LYP/6-31+ G（d，p）理论水平上，研究了苯甲酰胺（B）、N，N-二甲基苯甲酰胺（DB）、1-萘甲酰胺（N）和N，N-二甲基-1-萘甲酰胺（DN）在气相和溶液中的对映体生成机理.采用可极化连续介质模型--联合原子Hartree-Fock（PCM-UAHF）模型考虑了溶剂（DMSO、氯仿）的影响。发现了两种不同的机理，第一种是通过Ar-CO键的旋转和氮原子的反转进行的，第二种是Ar-CO和C-N的协同旋转。溶剂效应主要破坏具有协同旋转的过渡态（TS），这是由于这些结构中酰胺共轭的损失。用DMSO和氯仿作溶剂的结果表明，对于苯甲酰胺，通过反转的机理比通过协同旋转的机理分别有利14.1和13.2 kcal mol（-1）。当引入第二个环时，这种差异就会减小（对于N，分别为11.3和10.7 kcal mol（-1）），并且当N上的氢原子被甲基取代时甚至更高，使得对于DB，通过转化的途径分别为，5.5和4.8 kcal mol（-1）比Ar-CO和C-N协同旋转更有利，而对于DN，这一差异减小到1.1和0.6 kcal mol（-1），这使得两种机制在这种情况下实际上是竞争性的。
The mechanisms for enantiomerization in benzamide (B), N,N-dimethylbenzamide (DB), 1-naphthamide (N), and N,N-dimethyl-1-naphthamide (DN) were investigated both in the gas phase and in solution at the MP2-FC/6-311+G(d,p)//B3LYP/6-31+G(d,p) theory level. The effect of solvent (DMSO, chloroform) was taken into account by using the polarizable continuum model-united atom Hartree-Fock (PCM-UAHF) model. Two different kinds of mechanisms were found. The first kind proceeds through rotation about the Ar-CO bond and inversion at the nitrogen atom, while the second one consists of concerted Ar-CO and C-N rotations. Solvent effect destabilizes mostly the transition states (TSs) with concerted rotations owing to the loss of amide conjugation in these structures. According to our results using DMSO and chloroform as solvents, for benzamide, the mechanism through inversion is, respectively, 14.1 and 13.2 kcal mol(-1) more favorable than that through concerted rotations. This difference diminishes when a second ring is introduced (11.3 and 10.7 kcal mol(-1), respectively, for N) and even more when the hydrogen atoms on N are substituted by methyl groups so that for DB the route through inversion is, respectively, 5.5 and 4.8 kcal mol(-1) more favorable than that through concerted Ar-CO and C-N rotations and for DN this difference reduces to 1.1 and 0.6 kcal mol(-1), respectively, rendering both mechanisms practically competitive in this case.