Vicinal fluorine–fluorine coupling constants in perfluoropropyl groups

The geminal fluorines in XCF2–CF2Y groups are magnetically inequivalent. The fluorines comprise an AA′XX′ spin which should show non-first-order NMR spectra, but usually appear deceptively simple with little indication of vicinal coupling. Detailed analysis of the spectra of perfluorobutyric acid (1) and 2,2,3,3,4,4,4-heptafluorobutanol (2) are reported. The 3J(AX) and 3J(AX′) range between 4 and 9 Hz and are of opposite sign.