以NMR探討2-異丙基酚､乙醯苯胺及一些具有立體障礙的醇類經由氫鍵所產生的自結合現象

Abstract

摘要 本論文主要利用高解析度核磁共振光譜儀偵測稀釋溶液OH或NH之觀測位移 。這些隨濃度變化的化學位移的數據經由圖解法處理後可以分別求出單體位移 ，雙體位移 與雙體結合常數K。另外，利用雙體結合常數K隨溫度變化的關係，藉由van’t Hoff理論作圖可以求得各系統之標準結合熵( )和標準結合焓( )。 研究內容分為三部分。第一部份為：探討2-異丙基酚 (2-isopropylphenol，簡稱2-IPP) 在四氯化碳 (carbon tetrachloride)、丙酮-d6 ([2H6]acetone) 、氰甲烷-d3 ([2H3]acetonitrile) 以及二甲亞楓-d6 ([2H6]dimethylsulfoxide，DMSO-d6)等溶劑中經由氫鍵所形成的分子自結合 (molecular self-association) 行為。實驗結果顯示，2-IPP在丙酮-d6，氰甲烷-d3及DMSO-d6等溶劑中OH的化學位移不會隨濃度的增加而變化，此結果與在四氯化碳中所觀察到的現象相反。我們亦發現2-IPP在四氯化碳這類非極性溶劑中自結合較為重要。相反的在丙酮-d6､氰甲烷-d3及DMSO-d6等極性溶劑中反而溶質與溶劑間的異結合較為重要。 第二部分為：探討乙醯苯胺 (acetanilide) 經由N–H與 O=C所形成的氫鍵而造成的分子自結合（雙體）現象。所採用的溶劑有： 氯仿-d1 ([2H1]chloroform) 、丙酮-d6 ([2H6]acetone) 、氰甲烷-d3 ([2H3]acetonitrile) 及二甲亞楓-d6 ([2H6]dimethylsulfoxide，DMSO-d6)等四種溶劑。此四種系統分別在268至348 K溫度下進行實驗。經由NMR偵測乙醯苯胺在這些溶液中NH之觀測位移 。實驗結果顯示在此四個系統中單體位移、雙體位移和雙體結合常數K皆隨溫度的升高而減少。究其原因為乙醯苯胺在這些系統的雙體自結合過程皆為放熱反應。 第三部分為：討論三種具有立體障礙的脂肪族醇類 (aliphatic alcohols)，在非極性溶劑中經由氫鍵所形成的分子自結合（雙體）現象。所採用的系統有：2,4-二甲基-3-戊醇(2,4-dimethyl-3-pentanol) 或 3-甲基-3-戊醇 (3-methyl-3-pentanol)在環己烷-d6 ([2H12]cyclohexane)、四氯化碳與氯仿-d1 ([2H1]chloroform)溶液中等六個系統，以及2,3,4-三甲基-3-戊醇 (2,3,4-trimethyl-3-pentanol)在四氯化碳溶液中共七個系統。結果顯示標準結合焓( )的絕對值隨主鏈取代基的增加而下降，亦即3-甲基-3-戊醇＞2,4-二甲基-3-戊醇＞2,3,4-三甲基-3-戊醇。2,4-二甲基-3-戊醇與2,3,4-三甲基-3-戊醇在溶液中的的雙體結合常數K，標準結合焓以及標準結合焓的絕對值隨介電常數的增加而下降，亦即氯仿-d1＜四氯化碳＜環己烷-d12。

Abstract The self-association (dimerization) due to hydrogen bonding for some alcohols with bulky side chains, 2-isopropylphenol and acetanilide were investigated by nuclear magnetic resonance spectroscopy. The dilution shift data of OH or NH proton were measured and employed to determine the monomer shift, dimer shift and dimerization constant with the help of a graphic method. The enthalpy and entropy of dimerization were determined via a van’t Hoff plot from the temperature variation of the dimerization constant. This study includes three parts. Chapter 3 deals with the self-association of 2-isopropylphenol through hydrogen bonding in carbon tetrachloride, [2H6]acetone, [2H3]acetonitrile and [2H6]dimethyl sulphoxide. The proton dilution shifts of the hydroxyl group of 2-isopropylphenol in [2H6]acetone, [2H3]acetonitrile and [2H6]dimethyl sulphoxide do not change with increasing concentration, as opposed to in carbon tetrachloride From the concentration variation of the shift data, we conclude that the self-association of 2-isopropylphenol is more important in inert solvents while the hetero-association is more important in polar solvents. Chapter 4 deals with the study of the self-association of acetanilide through hydrogen bonding between N–H and O=C in the solvents [2H1]chloroform, [2H6]acetone, [2H3]acetonitrile and [2H6]dimethyl sulphoxide. We observed that the monomer and dimer shifts and dimerization constants all decrease with temperature in all these systems. Chapter 5 deals with the self-association (dimerization) due to hydrogen bonding for some alcohols with bulky side chains. The systems studied include 2,4-dimethyl-3-pentanol or 3-methyl-3-pentanol in [2H12]cyclohexane, carbon tetrachloride or [2H1]chloroform, and 2,3,4-trimethyl-3-pentanol in carbon tetrachloride. Experimental results indicate that the value of of 3-methyl-3-pentanol, 2,4-dimethyl-3-pentanol and 2,3,4-trimethyl-3-pentanol in carbon tetrachloride decrease when increasing the aliphatic substituents on the pentanol group. The dimerization constants, the values of - and - of the self-association of 3-methyl-3-pentanol and 2,4-dimethyl-3-pentanol reduce with increasing dielectric constants of the solvent, that is, [2H12]cyclohexane > carbon tetrachloride > [2H1]chloroform.