McClellan

Values of dipole moment y are listed in the compilation by McClellan (1974). 

McClellan, A. L., Tables of Experimental Dipole Moments, W. H. Freeman, San Francisco (1963-74). 

McClellan A L 1963 Tables of Experimental Dipole Moments vol 1 (New York Freeman)... 

Tables 5.17 and 5.18 contain a selected group of compounds for which the dipole moment is given. An extensive collection of dipole moments (approximately 7000 entries) is contained in A. L. McClellan, Tables of Experimental Dipole Moments, W. H. Freeman, San Francisco, 1963. A critical survey of 500 compounds in the gas phase is given by Nelson, Tide, and Maryott, NSRDS-NBS 10, Washington, D.C., 1967.

In their pioneer work, Brunauer and Emmett adopted the value a (Ar) = 13-8 for the molecular area of argon, by insertion of the liquid density Pi in the standard equation (2.27). The same figure was recommended by McClellan and Harnsberger " as a result of their comprehensive survey of the literature, already referred to. These workers noted that the recorded values of a (based on a (N2) = 16 2 A ) extended over the wide range 10-19 A, and concluded that the area occupied per molecule of argon in the completed monolayer varied from one adsorbent to another. 

McClellan s and Hamsberger s survey, which embraced a considerable variety of solids including carbons, metal oxides and organic polymers such as polythene, arrived at a mean value of 20-2 A, with a standard deviation of 1-6 A. Other more recent results, likewise based on = 16-2 A, ... 

Extrapolation from these two sets of values to C4 gives a (C4H,o) = 40-5 A for n-butane, which may be compared with the figure of 44-4 A (with a standard deviation of 4 A ) given in McClellan and Harnsberger s final list of recommended values and the value of 40 A found by Davis for n-butane on graphitized carbon at 195 K. A contributory factor to the variation in a -values is that the value of c tends to be low, e.g. on CaCOj (p. 251) c for butane is around 25. 

In their review McClellan and Hamsberger arrived at a recommended value of = 43 A with a standard deviation of 3A ... 

Experimental values are collected in the McClellan book (B-63MI40400) and in a review on dipole moments and structure of azoles (71KGS867). Some selected values are reported in Table 3. The old controversy about the dipole moment of pyrazole in solution has been settled by studying its permittivity over a large range of concentrations (75BSF1675). These measurements show that pyrazole forms non-polar cyclic dimers (39) when concentration increases and, in consequence, the permittivity value decreases. 

The dipole moment (A) of a molecule is the first moment of the elec tric charge density of a molecule. Paraffins have dipole moments of zero, while dipole moments of almost all hydrocarbons are small. McClellan lists many dipole moments. The computer method of Dixon and Jurs" is the most useful method for predicting dipole moments. Lyman et al. give other methods of calculation. 

Finally, we would like to express our thanks to the reviewers for their construe tive suggestions and to ACS Books Department staff members Catherine Buzzell and Maureen Rouhi, cover designer Eileen Hoff, and indexer Aubrey McClellan for their meticulous work and cooperation... 

McClellan, A.L. Tables of Experimental Dipole Moments Rahara Enterprises El Cerrito, Calif., 1974 Vol. 2, p 2. 

A. L. MCCLELLAN Editor, Teachers Guide California Research Corporation... 

For methods of determining dipole moments and discussions of their applications, see Exner, O. Dipole Moments in Organic Chemistry, Georg Thieme Publishers Stuttgart, 1975. For tables of dipole moments, see McClellan, A.L. Tables of Experimental Dipole Moments, vol. / W.H. Freeman San Francisco, 1963 vol. 2, Rahara Enterprises El Cerrito, CA, 1974. 

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