Experimental studies of the anomeric effect. Part IV. Conformational equilibria due to ring inversion in tetrahydropyrans substituted at position 2 by the groups ethoxy, 2'-fluoroethoxy, 2',2,'-difluoroethoxy, and 2',2',2'-trifluoroethoxy
作者:Harold Booth、Simon A Readshaw
DOI:10.1016/s0040-4020(01)89776-3
日期:1990.1
Equilibrium constants (K) for ring inversion equilibria in 2-(RO)-tetrahydropyrans (R=Et, CH2CH2,F, CH2CHF2 CH2CF3) have been determined from 13C nmr spectra recorded at 145–160K in CD2Cl2 and CFCl3/CDCl3 (85/15 by volume). Additional values of K were obtained at 250–270K from the acid-catalysed equilibration of is- and trans-2- (RO) -4-methyl tetrahydropyran (R as above). Plots of inK against T-1
由在145-℃记录的13 C nmr光谱确定了2-(RO)-四氢吡喃(R = Et,CH 2 CH 2,F,CH 2 CHF 2 CH 2 CF 3)中环反转平衡的平衡常数(K)。在CD 2 Cl 2和CFCl 3 / CDCl 3中为160K (按体积计为85/15)。K的其他值是在250-270K处通过异-和反-2-(RO)-4-甲基四氢吡喃的酸催化平衡而获得的(如上所述,R)。InK相对于T -1的图给出的R = Et,CH的ΔH° a→e值为-0.26,-0.12,-0.05和0.13 kcal mol -1在CD 2 Cl 2中分别为2 CH 2 F,CH 2 CHF 2和CH 2 CF 3。CFCl 3 / CDCl 3作为溶剂的ΔH° a→e的相应值分别为-0.58,-0.15,-0.07和0.21kcal mol -1。导出的ΔS°值在CD 2 Cl 2中分别为-2.33,-2