論文藉由ab initio理論計算的方法，以探討Thiohydroxamic acid分子
內質子轉移時的各項性質，及Hydroxamic acid與水分子間的質子轉移研
究。分別敘述如下：
第一單元 研究硫污酸中最簡單的分子形式Thioformohydroxamic acid
(S-HA)，並與其相似物Formohydroxamic acid(H-HA)做比較。研究結果
發現S-HA主要有5種異構物，以thiol form且具分子內氫鍵的S2Z最為
穩定。5種異構物之間的轉換，是由氮上的質子或氧上的質子轉移所構
成，總共有3條分子內質子轉移的路徑，分別會經過三環、四環和五環
的過渡結構，其能障的大小為三環＞四環＞五環，但比H-HA的能障來的
小，而過渡態的相對應角度大小的不同是造成能障較小的原因。由分子
內質子轉移位能曲線及陰離子的穩定程度可判斷S-HA在氣態的狀態下
應是N上的氫解離(N-acid)，與H-HA結果相同。另外探討推電子基(CH3)
和拉電子基(F)對H-HA做分子內質子轉移的影響，分別將接在
thiocarbonyl上的H取代成CH3和F，研究的結果發現取代基確實對質
子的親和力、質子轉移的能障有決定性的影響，當有推電子取代基時，
各路徑的活化能均降低;有拉電子取代基時，各路徑的活化能均上升。
第二單元 研究Formohydroxamic acid(FA)與水分子間的質子轉移，先
將FA的羰基質子化，然後分別將一分子的水擺在這個FA的三個官能基
(羰基，胺基，羥基)附近。接下來再加入一個水分子來探討，由
(H2OH．‥FA．‥OH2)+。為起始點，羰基當作質子接受者(proton acceptor)，而
胺基或羥基當做質子給予者(proton donor)，結果發現這兩個質子的轉移
並非是同步轉移的，而是會經由(H2O．‥FAH‥OH2)+的中間體，因此是
屬於逐步(Stepwise)轉移的過程。而至於是由胺基N上或羥基O上的質
子容易轉移給水，FA與水之間的距離是一個重要的因素。而在這個與
水分子的質子轉移過程與純粹分子內的質子轉移來比較，能障有明顯的
下降，代表水分子具有催化的作用。若將兩個水之間的距離拉長，使在
中間的質子化FA可以在兩個水分子間自由的移動，我們發現這個帶有
質子的FA分別與左、右的水分子作用，造成兩個低點的產生，而在這
中間移動則需跨越一個能障，這能障隨兩個水分子距離的增加而急遽增
加，然而FA與水分子的質子轉移能障卻和這兩個水分子的距離改變並
無多大關係。

This dissertation deals with the properties of intramolecular proton transfer of thiohydroxamic acid and intermolecular proton transfer of hydroxamic acid with water by ab initio methods. The descriptions are as followes:
Section 1: Thioformohydroxamic acid (S-HA), the simplest form of thiohydroxamic acid (SHAs), is investigated and its structure compared with the counterparts, formohydroxamic acid (H-HA). S-HA is found to have five tautomers, among which the S2Z, a thiol form with intra-molecular hydrogen bonding, is the most stable. The intramolecular-proton transfer is initiated by the proton connected on the nitrogen or oxygen. There are three possible pathways of the transfer; each of which has the transition structure containing either 3-, or 4-, or 5- member ring. The magnitudes of the energy barrier among them are 3-> 4-> 5- member ring but are all smaller than the corresponding transfer processes in H-HA. According to the potential energy surface of intramolecular proton transfer and the stability of the corresponding anion, we concluded that S-HA is an N-acid in the gas phase, similar result as that in H-HA. Besides, we also study the substitution effect to the intramolecular-proton transfer. The presence of the methyl substituent decreases the barrier, while that of the fluorine substituent increases it.
Section 2: Intermolecular proton transfer between Formohydroxamic acid (FA) and protonated water is also studied. In (H20H...FA...OH2)+ system, the carbonyl oxygen in FA is a proton acceptor, and that of hydrogen in amino or hydroxyl group is a proton donor. The result shows that the movement of these two protons is not simultaneous, but through stepwise processes. The proton on amino group or hydroxyl group easier transfering to the water molecule is determined by the distance between FA and the attached water molecule. Intramolecular proton transfer with the assist of water molecule largely decreases the energy barrier, indicating that water plays an importart role of catalyzation.
If we elongate the distance between the two water molecules, and let protonated FA move freely between the two water molecules, then this protonated FA will interact with the left and right water molecules respectively, to form two local minimums. The energy barrier for the movement of protonated FA is then very much dependent upon the distance between these two water molecules; however, the proton transfer barrier between protonated FA and water is independent of the distance between these two water molecules.