Substituenteneffekte auf die C–C‐Bindungsstärke, 8. Standardbildungsenthalpien und Spannungsenthalpien von 1,1,2,2‐Tetraethylethylenglykol‐dimethylether und D,L ‐1,2‐Dimethyl‐1,2‐diphenylethylenglykol‐dimethylether

Effects of Substituents on the Strength of C ‐ C Bonds, 8 1 . ‐ Heats of Formation and Strain of 1,1,2,2‐Tetraethylethylene Glycol Dimethyl Ether and D,L .‐1,2‐Dimethyl‐l,2‐diphenylethylene Glycol Dimethyl Ether The heats of combustion of the title compounds 1 and 2 were measured calorimetrically with the result (kcal mol ‐1 , s. d. in parentheses) Δ H ° c = − 1880.1 (± 0.6) and − 2373.3 (± 1.4). The heat of vaporisation of 1 Δ H v = 14.3 (± 0.3) and the heat of sublimation of 2 Δ H sub = 27.2 (± 0.5) were derived from their temperature dependance of the vapor pressure. The latter were determined between 30 and 80°C using a flow method. The resulting standard heats of formation Δ H ° t (g) = −122.4 (± 0.7) and −43.8 (±1.5) for 1 and 2 correspond to a strain enthalpy ( s ) of 15.9 and 8.0 kcal mol ‐1 , respectively. The steric strain of the dimethoxyethanes 1 and 2 is about one fourth lower than the strain of the corresponding dimethylethanes 3 and 4 bearing the same substituents. Thus, a methoxy group causes less steric stress than a methyl group.