Fluorine NMR. Spectra of conformationally constrainedGem-difluorocyclohexanes
作者:C. W. Jefford、D. T. Hill、K. C. Ramey
DOI:10.1002/hlca.19700530535
日期:——
3-difluorobicyclo [3.2.1]octane (IV). The Eyring parameters for the ring inversion were obtained for I and III. Representative values for the Arrhenius activation energy (Ea), ΔG‡, ΔH‡, and ΔS‡ are: 11.0, 9.4, 10.4 kcal/mole and 4.5 e.u. for I, and 10.0, 8.3, 9.7 kcal/mole and 8.3 e.u. for III. It appears that the syn-axial methyl-fluorine interaction has a negligible effect on the inversion process. However
测量了3,3-二甲基-(I),3,3,5-三甲基-(II)和3,3,5,5-四甲基-1,1-二氟环己烷的19 F化学位移和双键偶联常数(III)和3,3-二氟双环[3.2.1]辛烷(IV)。对于I和III获得了用于环反转的Eyring参数。Arrhenius活化能(Ea),ΔG ‡,ΔH ‡和ΔS ‡的代表值分别为:I分别为11.0、9.4、10.4 kcal / mol和4.5 eu,以及10.0、8.3、9.7 kcal / mol和8.3欧盟的III。看来,顺式-axial甲基氟相互作用对反演过程的影响可以忽略。但是,synIII中发现的α-轴甲基-甲基相互作用显着提高了转化率。标出了19 F移位的取代基效应。在赤道位置C-3处引入甲基会导致对赤道和轴向氟的屏蔽(+1.8和+ 1.3 ppm)。轴向C-3位置的取代引起赤道和轴向氟的屏蔽(-5.9和-4.9 ppm)。