Page 94 - Mechanism and Theory in Organic Chemistry

Thermochemistry 83

Table 2.10 (Continued)

Ring (o) AH," So

SOURCE: S. W. Benson, F. R. Cruickshank, D. M. Golden, G. R. Haugen, H. E. O'Neal, A. S.
Rodgers, R. Shaw, and R. Walsh, Chm. Rev., 69,279 (1969). Reproduced by permission of the Ameri-
can Chemical Society.

large number of compounds listed with their estimated and observed enthalpies
and entropies of formation.

Entropy
In this section we have so far emphasized only the AH0 and AH; of the reaction
components. This is because the entropy change in many reactions is small and
can often be neglected in comparison to the enthalpy change. When So's are of
interest, they too can be estimated by Benson's additivity rules. In order to cal-
culate So for a molecule, the group So contributions are added together just as
they are for AH;, but now a correction for the overall rotational symmetry (o) of
the molecule must be added. The correction is - R In a, where o is the product