Perfluorinated carboxylic acids (PFCAs) are a class of persistent environmental Pollutants Commercially available PFCAs are Mixtures of linear and branched isomers, possibly with impurities Different isomers have different physical and chemical properties and toxicities. However, little is known about the properties and the finer details of the Structures of the individual branched isomers. Full geometry optimizations for the linear n-alkane (C-6-C-27) PFCAs indicated that all have helical structures. The helical angle increases slightly with increasing chain length, from 16.3 degrees In C6F13COOH to 17 0 degrees in C27F55COOH. This Study predicts F-19 NMR parameters for 69 linear and branched isomers of the perfluoro carboxylic acids C6F13COOH, C7F15COOH, and C8F17COOH. B3LYP-GIAO/6-31++G(d,p)//B3LYP/6-31G(d,p) Was used for the NMR calculations with analysis of the chemical shifts by the natural bond orbital method. The predictions of the F-19 chemical shifts revealed the differences among the CF3, CF2, and CF groups. In general, the absolute values for the chemical shifts for the CF3 group are smaller than 90 ppm, for the CF larger than 160 ppm, and for the CF2 between 110 and 130 ppm. The chemical shifts of the branched isomers are smaller in magnitude than the linear ones. The decrease is correlated with the steric hindrance of the CF3 groups, the more hindered the CF3, the greater the decrease in the F-19 chemical shifts. The predicted F-19 chemical shifts are similar to those For analogous perfluoro compounds with other terminal functional groups such as -SO3H or -SO3NH2CH2CH3.