Effect of bulky substituents in the donor and acceptor terminal groups on solvatochromism of Brooker's merocyanine

Comparison of spectral properties of stilbazolium dyes in various solvents has exposed the influence of electrophilic and nucleophilic solvation on their solvatochromism.

Simulation of porphyrin-ethanol solvate shell by DFT method

Theoretical studies on porphyrin-ethanol solvates containing from 1 to 8 ethanol molecules have been carried out by density functional theory (DFT) calculations using hybrid (B3LYP) and meta-GGA (M06-L) functionals. It was established that porphirin molecule can be considered as two centered protones acceptor. Specific solvation is at the base of porphyrin-(EtOH)n interactions and results in a distortion of macrocycle planar structure. The nucleophilic solvation energy of the porphirin pyrrole demonstrates dependence on the number of molecules in the ethanol solvate, being the highest for the first two ethanol molecules and decreasing with ethanol association in the solvation shell. Results obtained by this way are in good agreement with data derived from 1H NMR.

Effects of solvent and structure on the reactivity of 6-substituted nicotinic acids with diazodiphenylmethane in aprotic solvents

The rate constants for the reactions of diazodiphenylmethane (DDM) with 6-substituted nicotinic acids in aprotic solvents at 30?C were determined. The obtained second order rate constants in aprotic solvents, together with literature data for benzoic and nicotinic acids in protic solvents, were used for the calculation of solvent effects, employing the Kamlet-Taft solvatochromic equation (linear solvation energy relationship - LSER) in the form: log k = log k0 + + s?*+ a? + b?. The correlations of the kinetic data were performed by means of multiple linear regression analysis taking appropriate solvent parameters. The sign of the equation coefficients (s, a and b) were in agreement with the postulated reaction mechanism, and the mode of the solvent influences on the reaction rate is discussed based on the correlation results. A similar contribution of the non-specific solvent effect and electrophilic solvation was observed for all acids, while the highest contribution of nucleophilic solvation was influenced by their high acidity. Correlation analysis of the rate data with substituent ?p parameters in an appropriate solvent using the Hammett equation was also performed. The substituent effect on the acid reactivity was higher in aprotic solvents of higher dipolarity/polarizability. The mode of the transmission of the substituent effect is discussed in light of the contribution of solute-solvent interaction on the acid reactivity.

Correlation of the rates of solvolysis of acetyl chloride and α-substituted derivatives

Additional specific rates of solvolysis have been determined for acetyl chloride and diphenylacetyl chloride. These are combined with literature values to carry out correlation analyses, using the extended Grunwald–Winstein equation with incorporation of literature values for solvent nucleophilicity (NT) and solvent ionizing power (YCl). Parallel analysis are carried out using literature values for the specific rates of solvolysis of trimethylacetyl chloride, chloroacetyl chloride, phenylacetyl chloride, and α-methoxy-α-trifluoromethylphenylacetyl chloride (MTPAC). Chloroacetyl chloride and MTPAC react by an addition-elimination pathway, with the addition step rate-determining, over the full range of solvents. Acetyl chloride reacts over the full range of solvents by an ionization pathway, with considerable nucleophilic solvation. The other three substrates can solvolyze with the domination of either mechanism, depending on the properties of the solvent. Reports concerning the use of product selectivity values, kinetic solvent isotope effects, and computational studies as additional probes of the mechanism of solvolysis are discussed.Key words: Grunwald-Winstein equation, acyl chlorides, mechanism of solvolysis, solvent nucleophilicity.