13C,19F and77Se NMR study of vicinal (E)-fluoro(organylseleno)olefins and [(E)-fluoroalkenyl]diorganylselenonium salts

Abstract

13C, 19F and 77Se NMR spectra of the (E)-fluoro(organylseleno)olefins R1(F)CαCβR2(SeR3) and the [(E)-fluoroalkenyl]diorganylselenonium salts R1(F)CαCβR2(Se+R3R4) X− were measured and assigned. The 13C, 19F and 77Se NMR chemical shifts, the 1JF,C and 2JF,C−β couplings, the vicinal 3JSe,F couplings, some selected 13C, 13C and 77Se, 13C couplings and the 19F, 13C couplings to the groups R1– R4 are discussed in relation to the structure of the compounds investigated. 1JF,C increases with deshielding of the 13C-α atoms of the fluoro(organylseleno)olefins and the fluoroalkenyldiorganylselenonium salts, i.e. both quantities are influenced by the same electronic effects. Linear Hammett correlations of para-substituted phenylseleno derivatives (R=MeO, Me, Ph, H, Cl, COOH, COOEt, CN; R1=R2=Et) between δ(13C-α), δ(13C-β), δ(19F), δ(77Se) and 3JSe,F, respectively, and σp values, and linear correlations between the experimental quantities δ(77Se)/δ(19F), δ(77Se)/3JSe,F and δ(19F)/3JSe,F (each with a positive slope) show that close relations exist (i) between the NMR chemical shifts within the FCCSe moiety and (ii) between the NMR chemical shifts (77Se, 19F) and the couplings 3JSe,F by alteration of the electron density in this structural element. The vicinal 3JSe,F coupling constant across the CC double bond (trans-coupling) is sensitive to structural alterations (<1 to 68.5 Hz). In the case of 1,1-difluorovinylphenyl selenide, F2CCHSePh, the 3JSe,F coupling constants obey the relation 3Jtrans > 3Jcis (40.8, 3.2 Hz). Copyright © 1999 John Wiley & Sons, Ltd.