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Signs of coupling constants in fluorinated cyclobutenes

1969; Elsevier BV; Volume: 1; Issue: 4 Linguagem: Inglês

10.1016/0022-2364(69)90078-x

1557-8968

Richard A. Newmark, G. Apai, R.O Michael,

Molecular Spectroscopy and Structure

The signs of all the fluorine-fluorine and hydrogen-fluorine coupling constants have been determined by homonuclear nuclear magnetic resonance spin tickling experiments in 1-ethoxy-2-chlorotetrafluorocyclobutene (II), 1,4-dichloro-3,3,4-trifluorocyclobutene (III), 3-chloro-3,4,4-trifluorocyclobutene (IV), 3-iodo3,4,4-trifluorocyclobutene (V), 1,4,4-trifluorocyclobutene (VII), 1-chloropentafluorocyclobutene (IX) and 1,2,4,4-tetrafluorocyclobuten-3-one ethylene ketal (X). Chemical shift calculations on III, IV, and V using electric field theory show that the cis vicinal JFF is negative and the trans JFF is positive in the CFX-CF2 fragment of the cyclobutene ring, for X = CI and X = I. Vicinal JFF across saturated bonds are negative in III and IV and positive in VII relative to the cross ring coupling. The vicinal and cross ring JFF between the vinylic and allylic fluorines is positive, and the cis coupling between the vinylic fluorines is negative in these cyclobutenes.