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  • The effective angular correlation geff

    2018-10-26

    The effective angular correlation (geff) between molecules is calculated using the modified form of Equation (5) (Undre et al., 2008). geff has been used to study the orientation of electric dipoles in binary mixtures. The Kirkwood equation for the mixture may be expressed aswhere geff is the effective Kirkwood correlation factor for a binary mixture, with фA and фB as the volume fractions of liquids A and B, respectively. The calculated values of geff using Equation (6) for all the systems at different concentrations are given in Tables 1–6 The geff value for pure amides is less than to unity, indicating the antiparallel orientation of dipoles and for alcohols, the geff values are higher than unity which is observed in the present study suggesting that the parallel alignment of the electric dipoles Patil et al. (1999). For mixtures, the geff values higher than one for different percentages of alcohols with amides increase with alcohol concentration recorded in the present study confirming the intermolecular association exists between alcohols and amides is significant Pieruceini and Saija (2004). The information related to solute–solvent interaction may be obtained by excess properties (Tabellout et al., 1990) related to the permittivity and relaxation times in the mixture. The excess permittivity εE is defined aswhere X is the Deacetylase Inhibitor Cocktail fraction and suffix m, A, B represent mixture, solute and solvent. The excess static dielectric constant may provide qualitative information about multimer formation in the mixtures as follows: Similarly, the excess inverse relaxation time is defined aswhere is the excess inverse relaxation time which represents the average broadening of dielectric spectra. The information regarding the dynamics of solute-solvent interaction from this excess property is as follows: The variation of excess permittivity (εE) with volume percentage of alcohols in amides is shown in Fig. 2. For lower alcohol region, positive deviations (εE) is noticed and are shown in Fig. 2, and this may be due to the amide molecules which may dissociate the alcohol molecules resulting in more monomeric species of alcohols and increase the total number of dipoles. In the increasing concentrations of alcohol, a negative (εE) deviation is noticed. This indicates the formation of multimer through hydrogen bonding, which leads to a decrease in total number of dipoles in the systems studied. This observation is in agreement with the results of Pawar and Mehrotra (2002) for DMF with chlorobenzene mixtures. The variation of excess inverse relaxation time ((1/τ)E) with volume percentage of alcohols in amides are shown in Fig. 3. The (1/τ)E of these system are positive in the lower alcohol region. This indicates a fast rotation of the dipoles. This may be due to formation of monomeric structures in this system. In the alcohol rich region these (1/τ)E values are negative. This suggest that the formation of multimer through hydrogen bonding, resulting in a slow rotation of dipoles. Similar results were reported by Helambe et al. (2000), for n-nitriles-methanol systems. It also follows from Figs. 2–3 that the NMA-alcohol systems have higher εE and lower (1/τ)E values than that of DMA-alcohol systems because of the inductive effect of the methyl group of amides increases in the order methyl to dimethyl, and the electron contribution of the methyl group to the CO group is significantly greater than that from the dimethyl group. Also the 1-decanol-amide systems have lower εE and higher (1/τ)E negative values than that of 1-butanol-amide, 1-pentanol-amide, 1-hexanol-amide 1-heptanol-amide and 1-octanol-amide systems, revealing that the tendency of complex formation is stronger in 1-decanol than that of 1-butanol. Because of steric hindrance, it is likely that long chain alcohols will have greater probability of complex formation due to head tail linkage, whereas for relatively smaller alcohols, the tendency is weakened due to switching mechanism prevalent in alcohol system (Dash et al., 2000). Therefore, one would expect that the strongest intermolecular hydrogen bonds would be formed between the CO group of NMA and the OH proton of 1-decanol and the weakest between the CO group of NMA and OH proton of 1-butanol and similar results are obtained in case of DMA-alcohols systems (Sivagurunathan et al., 2005c). This is reflected in the dielectric constant, the relaxation time, the Kirkwood correlation factor, and inverse relaxation time values.