Unsaturated Carbonyl Systems with a Terminal Vinylic CF2 Group

-Unsaturated Carbonyl Systems with a Terminal Vinylic CF2 Group 

CH2 = CHCF2H -113 2Jfh = 57, 3Jfh = PhCH =CHCF2H-108 2JFh = 56 

Notice that the CF2 fluorines of the Z-isomer of 4,4-difluoro-2-butene are significantly deshielded relative to those of the F-isomer. This is another probable example of steric deshielding by a proximate, in this case, cw-alkyl group (see Section 2.2.1). 

BENZENOID AROMATICS BEARING A CF2H OR CF2R GROUP 

Although direct phenyl substitution on a CF2H group leads to more than 10 ppm deshielding relative to CH3CH2CF2H, such benzylic  

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