Nature of the carbonium ion. I. The .pi.-route to a norbornyl cation from a thiocyanate-isothiocyanate isomerization

Abstract

Nmr single resonance spectra were obtained on Varían HA 100 ( ) and A56-50 (18F) spectrometers. ( 19), 19F(!H), and i9p(i»F) double-resonance experiments were performed on a Varían HA-60 instrument operating at 56.4 and 60.0 MHz. Octafluorocyclobutane, CCLF, CF2CICF2CI, and C6H5CF3 were used as lock signals for the 18F experiments. The necessary irradiating field for the heteronuclear decoupling experiments was provided by a NMR Specialties Model SD-60B heteronuclear spin decoupler. All of the benzotrifluorides 5 were obtained from Columbia Organic Chemicals., -DifluorotoIuene was prepared from benzaldehyde and SF4.16 , , -DifluorochlorotoIuene. In a three-necked, 250-ml flask equipped with a thermometer, gas inlet tube, and reflux condenser was placed 30 ml of , -difluorotoluene and 50 mg of azobisisobutyronitrile. The flask was then heated to 70°while chlorine gas was bubbled through the reaction mixture. The reaction was followed by 18F nmr and by testing the effluent gas for HC1 and was found to be over in about 90 min. The product was then distilled: bp 140°, 61°(50 mm); nmr (CC13) multiplet 5 7.5, 19F 49.36.2,3,4,5,6-Pentafluorobenzyl Fluoride. The apparatus consisted of a 250-ml, three-necked flask equipped with an addition funnel, a motor-driven stirrer, and an exit tube leading to a Dry Ice trap connected to a vacuum pump. The apparatus was flushed with dry nitrogen and then 48 g (0.2 mol) of finely powdered HgF2 was placed in the flask and 10 g (0.04 mol) pentafiuorobenzyl bromide (Penninsular Chem Research) was placed in the funnel.After evacuation of the flask the bromide was then added dropwise to the rapidly stirred mercuric fluoride over a period of 15 min. The product which collected in the Dry Ice trap was then filtered from a few grams of NaF, yield 1.8 g (45%). The nmr spectrum is given in Table IV.Decafluorobenzhydrol was obtained from Imperial Smelters Ltd. Tris(pentafluorophenyI)carbinol was a gift from Professor R.