• 作者： 王松茂
• 作者服務機構： 國立清華大學
• 中文摘要： 用NMR法研究2-甲基咪(口坐)(2MIm)及2,4二甲基咪(口坐)(DMIm)在氯仿溶液中之自重合作用以及此等咪(口坐)置換體與二甲基乙醯胺（DMA）間之氫鍵結合。2MIm與DMIm在氯仿溶液中除大多數分子以三重合體存在外，可能同時形成相當量之四重合體。在室溫時之三重合體形成係數為17.0及75.6 1. mole-1。與Im之三重合體形成係數(K3=27.1）相比較，自重合之安定次序為DMIm>Im>2MIm，而由此可推知1-N原子上氫之酸性（供氫度）及分子上甲基之立體障礙效應，為決定2MIm自重台之重要因素。由於二個甲基置換所誘起之3-N原子上之鹽基性（供電子度）優於其立體障礙效應而對於DMIm之自重合有利。 2MIm及DMIm與DMA間之氫鍵結合平衡係數在室溫各為4.29及4.35 l.mole-1。依其氫結合係數大小次序Im>DMIm>2MIm,，可知影響置換基咪(口坐)異分子間氫結合之重要因素為(1)咪(口坐)分子自重合之強度，(2)由於置換基之誘電效應所引起之供氫能力之減低，以及(3)置換基之立體障礙效應。 咪(口坐)分子之1-NH質子與甲醇、苯甲醇之OH質子及與2MIm之NH質子，交換甚快，在室溫時之質子交換活化能經初步估計，各為0.33，0.48及0.33 kcal. mole-1。
• 英文摘要： Self-associations of 2-methyl imidazole (2MIm) and 2,4-dimethyl im-idazole (DMIm) and their hydrogen bonding to N,N-dimethylacetamide(DMA) in chloroform have been investigated by NMR method. There area considerable amount of tetramer formed in addition to the trimer indespite of the fact that methyl group would hinder the self-association.The trimer constants were found to be 17.0 and 75.6 1. mole-1 at room tem-perature for 2MIm and DMIm. The order of the self-association constants,DMIm＞Im>2MIm (K3 for Im=27.1) indicates that the acidity of proton at1-N and steric hinderance play an important role for the self-association of2MIm and that the basicity of 3-N in DMIm favor its self-association. The associate constants for 2MIm and DMIm hydrogen bonding to DMAwere found to be 4.29 and 4.35 1. mole-1 at room temperature for 2MImand DMIM. The order of the hydrogen bonding constant, Im>DMIm＞2MIm, indicates that the magnitude of self-association, the decreasing strengthof proton donation by inductive effect of methyl group, and the stericeffect play important roles for the intermolecular hydrogen bonding associa-tion. The proton exchange between 1-NH proton of Im and OH protons ofmethanol，benzyl alcohol, and NH proton of 2MIm are quite rapid，andtheir activation energies were estimated to be 0.33, 0.48 and 0.33 kcal/moleat room temperature, respectively.
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