單重態環狀Nitrenium ions 以及其它等電子物種 ( Carbenes , Borenide anions ) 和H2O以及CH3OH分子的氣相反應之理論計算研究

Abstract

本論文藉由理論計算的方法，在B3LYP/6-31+G* 的計算層級下，探討環狀nitrenium ions、carbens以及borenide anions 與H2O以及CH3OH分子在氣相中的反應，探討各種可能的反應路徑，反應位向與能障的變化，並探討各系統所帶形式電荷不同所造成的影響。此外 ，並加入BVWN/6-31+G* 的計算層級下所得到的數據，作為B3LYP層級結果的對照。本文共分為以下二個部分進行研究：

第一部分 探討H2O在室溫下和環狀nitrenium ions、carbenes以及borenide anions反應的理論計算研究，計算結果發現主要的產物都是熱力學穩定的醇類衍生物。其中nitrenium ions以及carbenes都是以 insertion 反應為主要的反應路徑；而borenide anions雖然有進行insertion反應的可能性，但是主要的反應機制是經由abstraction反應抓走proton ( H+ )，形成中間產物H-BmR + OH—，而可能更進一步形成醇類衍生物。

第二部分 針對室溫下環狀nitrenium ions、carbenes以及borenide anions和CH3OH的反應作一系列的計算，探討所有可能的反應路徑。計算的結果發現， nitrenium ions和CH3OH可能進行C-H 鍵的insertion反應，形成熱力學穩定的醇類衍生物；也有可能經由O-H鍵的insertion反應，形成穩定的醚類衍生物。而主要反應機制是C-H 鍵的insertion反應。 Carbenes和 CH3OH的反應路徑，同樣具有C-H鍵以及O-H鍵的 insertion反應的二種可能性，但卻是以O-H鍵的反應為主要的反應機制。 而borenide anions和CH3OH的反應路徑，經由一系列計算的結果，並未發現O-H鍵insertion反應可能性，但是依然可以經由C-H 鍵的insertion反應，形成穩定的醇類衍生物。除此之外，我們發現borenide anions具有使C-O bond斷鍵的能力。反應過程中，B原子可以當成親核試劑，去攻擊CH3 group的C原子，造成C-O bond 的斷鍵；另外，B原子也可以當作親電子試劑，接受O原子上的lone pair 電子，形成B-O鍵，同時造成C-O bond的斷裂。但所有的反應路徑中，仍然是以C-H 鍵的insertion反應為主要的反應機制。This thesis deals with the calculation of the reaction of singlet cyclic nitrenium ions and isoelectronic analogues (carbenes, borenide anions) with H2O and CH3OH by density functional theory at B3LYP/6-31+G* level. This structures were then reoptimized with BVWN/6-31+G* level for comparison with the B3LYP results. There are two major sections for the reactions we studied and they are rendered here.

Section 1 We study the reaction of H2O with nitrenium ions, carbenes and borenide anions in gas phase. The result of the major products of the reactions are alcohol derivatives. It is apparent that all the reactions are thermodynamically exothermic. The main mechanisms of nitrenium ions and carbenes systems are O-H bond insertions, but those of borenide anions are abstraction reactions. Borenide anions will abstract the proton in water to form stable intermediates H-BmR and OH—, and then undergo toward forming alcohol derivatives.

Section 2 The reactions of CH3OH with nitrenium ions, carbenes and borenide anions are studied in this section. According to our results, nitrenium ions may undergo C-H bond insertions toward forming alcohol derivatives, or undergo O-H bond insertions toward forming ether derivatives. The main mechanisms of carbenes system are C-H bond insertions.

Similarly, carbenes may undergo C-H bond or O-H bond insertions, but the main mechanism is O-H bond insertion. In borenide anions system, there is no O-H bond insertion mechanism. In addition to C-H bond insertions, borenide anions can break the C-O bond in CH3OH. The B atom may act as a nucleophilic agent to attack the C atom in CH3OH，and then break the C-O bond . Or, the B atom may act as an electronphilic agent to accept the lone pair electrons on the O atom to form B-O bond and simultaneously break the C-O bond. However, in the reaction of borenide anions with methanol, C-H bond insertions are calculated to be the major process in the whole possible pathways.