Double relaxation times, dipole moments, energy parameters and molecular structures of some aprotic polar molecules from relaxation phenomena

The real epsilon (ij)' and imaginary epsilon (ij)" parts of complex dielect ric constant epsilon (ij)* of some aprotic polar molecules Ci) like dimethy lsulphoxide (DMSO) : N, N-diethylformamide (DEF) : N, N-dimethylformamide ( DMF) and N,N-dimethylacetamide (DMA) in benzene (i) for different weight fr actions w(j)'s of solutes are located at different temperatures under nearl y 10 GHz electric field together with the static and infinite frequency die lectric constants epsilon (oij) and epsilon (infinity ij). All the molecule s show the double relaxation times tau (1), and tau (2) for rotations of th eir flexible parts and the whole molecules by the single frequency measurem ent technique. The tau (1) in agreement with reported tau signifies that a part of the: molecule is rotating under 10 GHz electric field. It is also s upported by energy parameters DeltaH(tau), DeltaS(tau) and DeltaF(tau) meas ured from In (tau T) against 1/T curves for DMSO. The relative contribution s c(1) and c(2) towards dielectric relaxations for tau (1) and tau (2) are ascertained from Frohlich's equations and graphical technique. The correspo nding dipole moments mu (2) and mu (1) of the whole and the flexible part o f the molecule are obtained from tau (2) and tau (1) and the slope beta of high frequency conductivity sigma (ij) against w(j) in order to compare wit h the measured static mu (s) and reported mu 's. mu (1)'s are found to agre e with mu (j) and static mu (s) The molecular conformational structures are obtained by mu (cal) from mu (s)/mu (theo) by considering mesomeric and in ductive effects of the substituent polar groups. mu (theo)'s are obtained f rom available bond moments and bond angles. The comp arisen of ail the mu ' s shows little dependence on electric field frequency. (C) 2000 Elsevier Sc ience B.V. All rights reserved.