Hydrogen Bonds On The Acid-base Ionization Constants Of The Impact Theory

Hydrogen bonding plays a critical role in a wide range of chemical and biological phenomena. The hydrogen bonds not only affect the structure and stability of molecular and biomolecular complexes, but also influent many chemical, physical, and biological processes. Bring the hydrogen-bonded theory to the acid-base scale as the new subject which has attracted considerable attention over the years. The theoretical study of the organic's pKa value is can supply the experiment test method, it also disclosures the phenomenon and the essence of ionization more and more. So, it will be very interesting and guiding meanings subject. And it is expected to make some theoretical studies of the organic's pKa value, as to make up for the experiment shortage.In this paper we first studied the hydrogen-bonded complexes, used thehigh-level ab initio approaches to study the cysteine-formamide complexes. The optimized geometric parameters, interaction energies and the infrared spectrum frequencies, IR intensities are investigated. Next, in the nonpolar solvent (dimethyl sulfoxide) we used the different methds (involve the B3LYP, MP2 and HF methods) and the polarizable continuum model (PCM) to study the pKa value of the organics which have different functional groups. We want to know which method adapts to sudy the pKa. In the last chapter, we used the cluster-continuun model which base on the hydrogen bond to study the pKa, at the some time, discussed the optimal number and the position of the solvent molecule.This paper studied the structure, frequency and IR spectrum of the cysteine-formamide complexes, next we found the HF method is fit to study the pKa value. The number and the position of the solvent molecule in the cluster also can affect the organic's pKa value.We discussed the the theoretical method and model to studied the organic's pKa value, it has meaning to guide the experimentations and further theoreticalstudy in the future.