Acetic acid dimer, dipole moment

The agreement between calculated and observed values of Table 20 is comparable to that obtained in Table 17 for the select solvents, except for water and alcohols. The latter solvents self-associate through H bonds to form very polar clusters giving rise to much larger (b values than might be anticipated from the permanent dipole moments of the monomers. Evidently, the formation of cyclic acetic acid dimer does not produce such an effect so that this hydroxylic solvent has normal values of both 0(c ) and fi—very similar to those for the aprotic derivatives methyl and ethyl acetates. 

Acetanilide, electrophilic aromatic substitution of, 939-940 Acetate ion, bond lengths in, 43 electrostatic potential map of, 43, 53, 56, 757 resonance in, 43 Acetk acid, bond angles in, 755 bond lengths in, 755 dimer of, 755 dipole moment of, 39 electrostatic potential map of, 53, 55... 

The most stable structure of the smallest hydration compound of acetic acid monomer, as well as the acetic acid water dimer, has a four-membered head-on ring with the smallest dipole moment. To verify the existence of it, the infrared spectra experiment data were collected in the dilute CCU/HAc and CCI4/H2O ratios condition. The hydroxyl (O-H) stretching vibrations in molecules of water, acetic acid, and the dimer are distinguished, for the dissolved species are isolated from each other by surrounded solvent molecules CCI4. The calculated and measured vibration frequencies are almost lain in line with 0.872 scaling. 

For the application system involving acetic acid in Chapter 9, the above representation in Eq. (2.3) is not accurate enough. The reason is that acetic acid can exhibit association leading to dimerization in the vapor phase. Hayden and O Connell used the virial equation of state tmncated after the second term. They developed a correlation for the second virial coefficient of polar, nonpolar, and associating species based on the critical temperamre and pressure, the dipole moment, and the mean radius of gyration. Association of like and unlike molecules is described with the adjustable association parameter. Pure component and binary values for the association parameter are available in the Aspen Physical Property System. For detail calculations in the vapor phase, please refer to the above Hayden and O Connell paper and also to Aspen Physical Property System. ... 

Acetic acid vapor contains a proportion of planar, hydrogen-bonded dimers (23). The apparent dipole moment of molecules in pure gaseous acetic acid increases with increasing temperature. Suggest an interpretation of the latter observation. 

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