C-13 CHEMICAL-SHIFTS OF THE POLYPROPYLENE MODEL COMPOUNDS 3,5-DIMETHYLHEPTANE AND 3,5,7-TRIMETHYLNONANE

13C-NMR chemical shifts are calculated for the stereoisomers of the polypropylene model compounds 3, 5-dimethylheptane (A) and 3, 5, 7-trimethylnonane (B). Differences in the chemical shifts of the same carbon atom in the various stereoisomers are attributed to stereosequence-dependent differences in the frequency with which the given carbon atom is involved in 3 bond gauche or γ interactions with other carbon atoms. The Suter-Flory RIS model of polypropylene is employed in the evaluation of the number of γ interactions involving each of the carbon atoms in A and B. The calculated 13C chemical shifts are compared to the observed values and those calculated previously for 3, 5, 7, 9, 11, 13, 15-heptamethylheptadecane. This comparison permits an assessment of the utility of A and B as model compounds for polypropylene. © 1979, American Chemical Society. All rights reserved.