臺灣博碩士論文加值系統

在有機金屬的研究中碳氟鍵的活化一直是個令人感興趣的題目,特別是氟取代丙基的碳氟鍵，其展現了不同於在氟取代甲基、乙基中的反應性。氟取代甲基與乙基中被活化的碳氟鍵是α位置的碳氟鍵，但是在氟取代丙基中活化的位置卻是β位置的碳氟鍵。本文中我們試圖在超高真空的環境下,分別以部分氟取代丙基碘（CF3CF2CH2I、CHF2CF2CH2I、CF3CH2CH2I）及全氟取代丙基碘（n-C3F7I、i-C3F7I）為前趨物，在Cu(111)表面上產生氟取代丙基（CF3CF2CH2(ad)、CHF2CF2CH2(ad)、CF3CH2CH2(ad)、 n-C3F7(ad)、i-C3F7(ad)），並利用程溫脫附反應（Temperature-Programmed Desorption，TPD）進行此課題的研究。首先，在針對部分氟取代丙基之β消去反應動力學的研究中我們發現由於互疊構型作用力eclipsed interaction）之影響使得CF3CF2CH2(ad)（200 K）、CHF2CF2CH2(ad) （190 K）兩物種都能在相當低的溫度下行β消去反應。但此二者行β消去反應的活化能又有些微的不同，根據Gellman 等人所提出之過渡態電荷分佈模型（Cβ+δ…H−δ…M+δ），我們認為此些微之能差便是由於Cβ上之甲基的陰電性不同造成過渡態Cβ之正電荷不穩定的結果。接著比較β-F 以及β-H 消去之反應速率，實驗結果顯示β-F 消去反應之速率遠較β-H 消去反應快。將β-H 消去反應之過渡態電荷分佈模型套用到β-F 消去反
應（Cβ+δ…F−δ…M+δ），我們發現此活化能的差異乃是起因於Fluoride-like 的過渡態較為穩定，即β-F 消去反應較β-H 消去反應有較低的活化能、較高的III反應速率。最後的部分是關於全氟取代丙基的研究，本研究中我們對兩種全氟取代丙基的同分異構物進行TPD 反應、PIR 的研究並配合DFT 計算以推測出此二物種在表面之吸附構型的差異。TPD 的結果顯示n-C3F7(ad)在340 K時Cu-C 鍵斷裂形成radical（n-C3F7．）脫附，至於i-C3F7(ad)則是行β-F 消去反應生成CF3CF=CF2 脫附。此結果意味著i-C3F7(ad)的Cu-C 鍵能較n-C3F7(ad)高，反應在構型上的差異便是i-C3F7(ad)的Cu-C 鍵長較短。DFT 計算IR 光譜結果亦印證了此推測。此外，由於i-C3F7(ad)擁有較多的β-F 使得i-C3F7(ad)受前指數因子影響β-F 消去反應會較其他路徑更具優勢。

In organometallic study, activation of C-F bond is an interesting subject, especially in fluoro-substituted propyl groups, because of their different reactivityn from fluoro-substituted methyl and ethyl groups. In this thesis, fluorinated propyl groups were studied on a Cu(111) surface under ultrahigh vacuum (UHV)
conditions. We have examined the kinetics of the β-elimination reaction in CF3CF2CH2-Cu, CHF2CF2CH2-Cu, and CF3CH2CH2-Cu. These species all
decompose via β-elimination to give CF3CF=CH2, CHF2CF=CH2, and CF3CH=CH2. The first two species undergo β-fluoride elimination and the third
one undergoes β-hydride elimination. The difference in activation energies between the first two accounts for the charge separation (R-Cβ+δ…F−δ…M+δ) in the transition state proposed by Gellman. The activation energies for β-hydride
elimination (CF3CH2CH2-Cu) and β-fluoride elimination (CF3CF2CH2-Cu) was also compared. The activation energy for β-fluoride elimination is found to be lower than that of β-hydride elimination. In the studies of reaction pathways for perfluoropropyl groups (n-C3F7-Cu and i-C3F7-Cu) on Cu(111), we discovered novel chemistry in TPD. n-C3F7-Cu undergoes Cu-C homolytic cleavage (radical desorption) at 340 K, whereas i-C3F7-Cu eliminates the β-fluorine at 365 K. By
changing the Cu-C bond length in the i-C3F7-5Cu models their IR spectra was calculated. We discover that the IR of i-C3F7-5Cu with shorter Cu-C bond (1.728Å) is more similar to the experimental IR spectra. That demonstrates the bond strength of Cu-C bond of i-C3F7-Cu is too strong to undergo Cu-C homolytic cleavage at 340 K. Hence, β-F decomposition becomes the favorite pathway to i-C3F7-Cu because there are more β-F atoms available in this moiety.

Chapter 1 Introduction……………………………………………………. 1
Chapter 2 Experiments……………………………………………………. 3
Chapter 3 Results
3.1 TPD spectra of CF3CF2CH2I, CHF2CF2CH2I, and CF3CH2CH2I
on Cu(111)……………………………………………………… 5
3.2 Novel Reaction pathway for Perfluoropropyl iodide on Cu(111). 12
3.3 IR Spectra of CF3CF2CH2I and CHF2CF2CH2I on Cu(111)……. 19
3.4 IR Spectra of CF3CH2CH2I on Cu(111)………………………… 23
3.5 IR Spectra of CF3CF2CF2I on Cu(111)…………………………. 26
3.6 IR Spectra of CF3CFICF3 on Cu(111)………………………….. 30
3.7 DFT Computation for IR spectra……………………………….. 32
Chapter 4 Discussion
4.1 β-F elimination in Fluoropropyl Groups on Cu(111)…………... 39
4.2 β-F elimination vs. β-H elimination……………………………. 41
4.3 Reaction Pathways of n-C3F7 and i-C3F7……………………….. 43
Chapter 5 Conclusions…………………………………………………….. 45
References ………………………………………………………………….. 47

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