Properties of the Reference Compounds

Occasionally one may be interested in calculating thermodynamic properties for a large compound that differs only slightly from one for which data are already known. (This is more likely to occur when dealing with substituted alkanes than with unsubstituted ones.) In such a case, it may save some calculations to begin with the known properties of the reference compound and then make appropriate corrections for the groups that have to be added or subtracted to get to the compound of interest. For example, if one needs for 3-ethyl-4,5-dimethyloctane but knows the value for 3,4,5-trimethyloctane, one simply adds the entropy contribution for an S [ = C-(C)2(H)2] group. 

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