| Summary: | 碩士 === 國立交通大學 === 應用化學系碩博士班 === 99 === The self-association of 2-Acetyl-3,5-dimethylpyrrole (ADP) and Ethyl 3,5-dimethyl-1H-pyrrole-2-carboxylate (EDPC) in various solvents have been studied using infra-red spectra. The molar absorption coefficient of N-H stretching for ADP monomer and ADP dimer are obtained from the equation derived from the concentration dependent integrated absorbance of monomer bands and those of dimer bands, respectively. So does the dimerization constant obtained independently from them. The letter offers an opportunity to check the consistency of the determination.
As for EDPC, the spectra is found that two N-H bands exist in monomer region. This system is a monomer-dimer self-association accompanying a cis-trans inter-conversion in monomer. Our three linear plots respectively for cis, trans monomer and dimer bands are unable to give the molar absorption coefficients of cis and trans monomer N-H stretching εC, εt and cis-trans interconversion constant K1, dimerization constant K2, except for the molar absorption coefficient of dimer band. To overcome this difficulty, we resort to quantum chemical calculation using PBE1PBE/6-311++G** functional to give the ratioεC/εt. The letter enables us to estimate K1 from the ratio of integrated absorbance At/AC. With K1 known, other parameters K2, εC andεt can be solved. The solvent effect on the frequency shift, band width, band intensity and enthalpy of dimerization are also discussed.
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