利用理論計算方法探討HCNC自由基和 NO之反應機制

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Title:	利用理論計算方法探討HCNC自由基和 NO之反應機制
Authors:	李奇蓁
Contributors:	應用化學研究所
Keywords:	初使法硬軟酸鹼理論
Date:	2010
Issue Date:	2011-10-31 15:08:36 (UTC+8)
Abstract:	本篇我們使用初使法 (Ab initio)來探討Isocyanocarbene (HCNC)與NO的反應機構研究。使用B3LYP/6-311++G(3df,2p)幾何最佳化與單點能量CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311++G(3df,2p)，計算並繪於反應位能曲面圖(PES)。在所有路徑當中，以產生P2 (HCNO + CN)與P3 (HCN + NCO)為兩種主要路徑。前述P2路徑中，反應先進行HCNC 與 NO加成反應，產生IM3，反應過程放熱61.49 kcal/mol，接著跨越12.32 kcal/mol的反應能障 (TSiso1)，而形成中間產物IM2，而IM2則直接產生最終產物P2 (HCNO + CN)，而整體放熱為12.68 kcal/mol。對於P3路徑，中間產物IM3進行另一條反應路徑，跨越21.45kcal/mol的反應能障 (TS2)，形成五員環產生IM7，之後IM7進行開環反應，跨越6.31 kcal/mol的反應能障 (TS5)，而產生IM9，斷C－N鍵，接著跨越53.39 kcal/mol的反應能障 (TS7)，形成最終產物P3 (HCN + NCO)，此路徑共放熱98.63kcal/mol。為了有效地解釋計算結果，我們使用Fukui functions和硬軟酸鹼理論 (HSAB)，而尋找上述可能現象。 The mechanisms of the reaction of the Isocyanocarbene radical (HCNC) with the NO have been investigated by ab initio molecular orbital method. The relevant stationary points and potential energy surfaces (PESs) were calculated by the B3LYP/6-311++G(3df,2p) and CCSD(T)/6-311++G(3df,2p)//B3LYP/6-311G(3df,2p) levels, respectively. Products P2 (HCNO + CN) and P3 (HCN + NCO) are two leading channels with slight energy barriers as compared to the reactants HCNC + NO. In the former path (P2 formation), HCNC and NO undergo bond addition reaction and then produce IM3 with exothermicity of 61.49 kcal/mol. It will then overcome a barrier height of 12.32 kcal/mol (via TSiso1) forming an intermediate, IM2. The IM2 can directly produce the final products P2 (HCNO + CN) via one variational transition state with an overall exothermicity of 12.68 kcal/mol as compared to the reactants HCNC + NO. For the path of P3 formation, however, the IM3 intermediate will proceed another pathway, via TS2 (Ea=21.45 kcal/mol), to form five-membered ring intermediate, IM7, and then open the ring by passing a barrier (via TS5, 6.31 kcal/mol) forming another intermediate, IM9. The IM9 will break its C-N bond (via TS7, 53.39 kcal/mol) and form the final products of P3 (HCN + NCO), with an overall exothermicity of 98.63 kcal/mol. To effetely rationalize the scenario of the calculated results, we also employ the Fukui functions and HSAB theory to seek for the possible explanation of the aforementioned phenomena.
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