Structure of charged cyclohexyldiamines in aqueous solution: a theoretical and experimental study
A J Lopes Jesus1, M Helena S F Teixeira, J S Redinha
1Faculty of Pharmacy, University of Coimbra , 3004-295, Coimbra, Portugal.
Abstract:
The structure of mono- and diprotonated cyclohexyldiamine isomers in aqueous solution is investigated theoretically by the application of the CPCM continuum solvation model combined with the MP2/aug-cc-pVDZ model chemistry. The calculated Gibbs energy of hydration (ΔGhyd) is expressed in different terms with physical meaning: cavity formation, solute conformational variation, and solute-solvent interaction. Significant differences of the ΔGhyd values are found among isomers, which are interpreted based on the analysis of the factors accounting for the stability of the conformers/isomers in the gas and solution phases. Particular attention is given to the role played by the formation of an intramolecular hydrogen bond in the monoprotonated forms and by the Coulombic repulsion between the NH3(+) groups in the diprotonated ones. From the Gibbs energies of the acid/base pairs in the gas phase and respective hydration Gibbs energies, the acidity constants (pKa) are calculated and interpreted. For some isomers, the constants are also determined experimentally by potentiometric titration. A good agreement was found between the calculated and experimental values.
More Related Videos
11:45Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles
Published on: August 22, 2018
09:45Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene
Published on: March 20, 2017
Related Concept Videos
Aromatic Hydrocarbon Cations: Structural Overview
Removing one hydrogen from the intervening CH2 group with both...
Stability of Substituted Cyclohexanes
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
Aromatic Hydrocarbon Anions: Structural Overview
Due to the absence of continuous overlap of p...
Basicity of Heterocyclic Aromatic Amines
Nomenclature of Primary Amines
Aryldiazonium Salts to Azo Dyes: Diazo Coupling
