甲醯胺及其衍生物的分子內和分子間及與水氨分子間的氫原子轉移理論計算研究

Theoretical Study of Intra- and Inter- molecular Hydrogen Transfer of Formamide and Its Derivatives Together with Water/Ammonia Molecules

郭進祥(Guo Jin Xiang)

指導教授 ： 何嘉仁

國立臺灣師範大學/理學院/化學系/博士(2000年)

摘要

中 文 摘 要
本論文藉由ab initio 及DFT理論計算的方法，探討甲醯胺及其衍生物在有無催化劑時，分子內氫原子轉移的各項性質，及質子化甲醯胺、氨分子衍生物之分子間質子轉移理論研究。分別敘述如下：
第一部份 包含第2、3、4單元，研究具有peptide bond型態HNC=O的最小分子甲醯胺及其以CH3、OH、OCH3取代之衍生物的分子內氫原子轉移的性質，以作為較複雜系統的基本模型。甲醯胺分子中有氮上的氫原子經過四環過渡狀態和碳上的氫原子經過三環過渡狀態轉移至氧原子上兩種路徑(FN和FC)，FN的能障較低，FC的能障較高。FN路徑有碳和氮二個位置的氫可被取代，在碳上的取代都使能障下降，在氮上則有取代基效應，即推電子基(CH3)使能障下降，拉電子基(OH、OCH3)使能障上升。FC路徑氮上有二個氫原子可被取代，與氧同一邊的Z位置和與氧不同一邊的E位置，Z位置取代都使能障下降，無取代基效應，E位置有取代基效應。甲醯胺分子旁邊有H2O、NH3可幫助使氫原子轉移能障下降。
第二部份 第5單元研究質子化甲醯胺與H2O或另一個甲醯胺的分子間質子轉移。質子在不同距離的分子之間轉移，距離越大，質子轉移能障越高。若兩個甲醯胺分子以碳鏈(-CH2-)相聯，並未因碳鏈數增加而使質子轉移能障升高。若二個相當長距離的甲醯胺之間有H2O當作質子攜帶者，則幫助質子轉移，使能障降低。
第三部份 附錄A研究質子在兩個氨分子及其氟、甲基取代衍生物分子間轉移的性質，由於主題與前兩個部份較不同，所以置於附錄中。本單元藉由 ab initio 理論計算的方法，探討質子在兩個NH2A、NH2B ( A , B = H , F , CH3) 分子間轉移的性質。在MP2/6-31G(d)層級得到A = H , B = F及A = H , B = CH3的質子化雙聚體系統中，質子是靠在質子化能較大的一邊，質子轉移曲線因兩邊質子化能相差較大是單位能井。A與B相同分別為H , F , CH3質子轉移曲線則是雙位能井。未取代時 ( A , B = H )質子恰在兩個氮原子的連線上，即 d(NRNLHm) = 0o，氟原子取代時 d = 19.3o，甲基取代時 d = 0.5o質子轉移時兩個氮原子間的距離分別由2.731、2.708及2.735 Å 縮小至2.614、2.593及2.614 Å。其質子轉移的能障分別是1.10、2.30及1.13 kcal/mol。拉電子基(F)及推電子基(CH3)都使能障升高，F的取代使能障升高較多。

關鍵字

甲醯胺 ； 分子內 ； 分子間 ； 氫原子轉移 ； 氨分子 ； 質子轉移 ； 能障 ； 取代基效應

並列摘要

Abstract
This dissertation deals with the properties of intramolecular hydrogen transfer of formamide and its derivatives with or without catalyst and intermolecular proton transfer between protonated formamides, and between ammonia derivatives by ab initio and DFT methods. The descriptions are as following：
Part 1 In section 2, 3 and 4 of the dissertation, the properties of intramolecular hydrogen transfer of formamide, the smallest molecular involving HNCO peptide bond, and its CH3 , OH , OCH3 substituted derivatives are studied as a basic model for more complicated systems. There are two possible pathways of hydrogen transfer in formamide, namely FN and FC. The process of transfering a hygrogen from a nitrogen atom to the carbonyl oxygen of formamide with the four member ring transition state is denoted as path FN , while the similar process from the carbon atom with the three member ring transition state is denoted as path FC . Path FN has lower barrier than path FC. There are two possible substitution sites in path FN , carbon and nitrogen. The carbon-site substituents all could reduce the barriers while the nitrogen ones show substitution effect, i.e. the electron-releasing substituent ( CH3 ) would decrease the energy barrier, while the electron-withdrawing substituent ( OH, OCH3 ) would increase. In path FC, there are also two possible substitution sites, Z form ( substituent on the same side as carbonyl oxygen ) and E form ( substituent on the opposite side ). Z form all has lower barriers, but E form show substitution effect. The catalytic effect can be achieved by adding H2O or NH3 molecule to the formamides .
Part 2 Intermolecular proton transfer of protonated Formamide with H2O or the other formamide was investigated in section 5. Proton transfers between two moleculars of several fix O-O distances causes different energy barriers. The larger O-O distance, the higher is the energy barrier. If two formamide moleculars were connected with carbon chain ( -CH2-), the increase of the number of carbon chain would not proportionally increase the proton transfer energy barrier. In case that the distance between two formamide moleculars was too large, the existance of a H2O as a proton carrier would decrease the energy barrier.
Part 3 The properties of proton transfer between two ammonias or between two fluoro-, methyl-substituted ammonia-derivatives were investigated in appendix A. Ab initio theoretical method was performed to calculate the proton transfer property of ( NH2AHNH2B)+ complex ion ( where A, B = H, F, and CH3 ). In the complex ions where A = H, B = F and A = H, B = CH3 , the proton resides on the site of the NH2X unit ( X = A or B ) whichever has greater proton affinity. The potential profile thus becomes a single well. However, if A = B, either H, F, or CH3 , there exists two minima and a double well potential forms in the process of proton transfer of the complexes. In ( NH3HNH3)+ the proton resides on the line connecting the two N atoms, that is d(NRNLHm) = 0o，whereas in (NH2FHNH2F)+ , d = 19.3 o , and d = 0.5 o in (NH2CH3HNH2CH3)+ ion. The distanse of the two N atoms shrinks during the process of proton transfer, such as 2.731, 2.708, and 2.735 Å for A, B = H, F, and CH3, respectively, to 2.614, 2.593, and 2.614 Å. The barriers for proton transfer are 1.10, 2.30, and 1.13 kcal/mol for A, B = H, F, CH3, respectively. Proton transfer proceeds with greater difficulty in fluoro-substituted complex than in the non-substituted and methyl-substituted complexes.

並列關鍵字

ab initio ； DFT ； CH3、OH、OCH3

參考文獻

ARRAY(0xa22b574)