Solvent Effect Upon Dipole Moment and Proton Transfer Equilibrium in Ortho Mannich Bases

Abstract

The dipole moments of ortho Mannich bases containing intramolecular OH...N hydrogen bonds were determined in solvents of various electric permittivity. The dipole moment of 2-(N8N-diethy1aminomethy1)-3,4,6-trich10ropheno1 does not depend on the solvent polarity and simultaneously no contribution of the proton transfer form was detected in ultraviolet-visible spectra. The dipole moments of 2-(N8N-diethy1aminomathy1)-3,4,5,6-tetrach1oropheno1 and 2-(N,N-diethylaminomethyl)-4-nitronaphtol-l increase distinctly with the solvent polarity. The dipole moment enhancement can be quantitatively correlated with the displacement of the OH...N * O-...H-N+ equilibrium towards tho more polar proton transfer form. The solvent influence on the free energy of the proton transfer process, bGpT, is discussed in terms of various effects.

Mannich Bases as Model Compounds for Intramolecular Hydrogen Bonding II [1]. Structure and Properties in Solution

“…From that it follows that in solutions of such Mannich bases no aggregation of the zwitterionic structures occurs. The in¯uence of the solvents electric permittivity increase on dipole moments has been studied as well [20]. For a compound with a ÁpK a of 2.72, no such dependence was found up to a permittivity of 10.…”

“…6-(N,N-diethylaminomethyl)-2,3,4,5-tetrachlorophenol (ÁpK a 3.04) does not show any association over the whole concentration range (up to 4 Á 10 À2 mol Á dm À3 ) in benzene solutions at room temperature. About 9% of the ionic form were found in benzene at room temperature [20]. An increase of the temperature within the range of 283±328 K leads to a decrease of the polarity of the hydrogen bond from 1.95 to 1.63 D caused by a decrease of the amount of ionic forms [21].…”

“…For example, the amount of ionic species of 6-(dimethylaminomethyl)-2,3,4,5-tetrachlorophenol in CCl 4 at room temperature calculated from this equation is 6% which is in accordance with the results discussed in Refs. [20,21,51]. The IR results [3] show a pronounced increase of the Á#(OH) values for Mannich bases in CCl 4 at room temperature at ÁpK a %4.…”

Internal and External Implications of the Structure of Hydrogen Bonded Complexes . Ii. Mndo‐pm3 Studies on the Structure of the 4‐methylpyridine Complex With Pentachlorophenol

“…The MOPAC.5 package with implemented by Szafran et al Comparison of structural parameters of the hydrogen bond in II and I (in parentheses) calculated for the planar conformations (#J = 0) [16], or the electronic spectra of the system [17]. The increase of the permittivity to 2.238, simulating the system transfer from the gas phase to typical nonpolar solvent (CC14) results in a significant decrease in AWf difference between PT and HB states, but only HB forms will exist in such solution.…”

Gas Phase Computational Study of Diclofenac Adsorption on Chitosan Materials

“…However one should realize, that in general, solvent presence can strongly affect the geometry of the investigated systems, their energetics, electronic properties and-what is of great importance-the characteristics of the created hydrogen bonds between the subunits of the investigated molecular complexes [32][33][34][35][36][37]. The numerous evidences of the modification of molecular spectroscopic properties, NMR chemical shifts, weak intra-and intermolecular interactions or proton transfer processes can be found for instance in older as well as more recent works by Sobczyk et al and Limbach et al [37][38][39][40][41][42][43]. Therefore, it can be crucial to include the solvent effects in computational studies in order to obtain quantitative correspondence to the experimental results.…”