Geminal Substituent Effects. VIII. Enthalpies of Formation od Acetals

Article abstract of DOI:10.1002/prac.19953370122

The standard enthalpies of combustion ΔH^o_c(1 or c) of the α-phenyl-substituted acetals (1) and diacetals (2) were measured calorimetrically.The enthalpies of vaporisation or sublimation ΔH_vap or ΔH_sub of 1-2 were obtained from the temperature function of the vapor pressure measured in a flow system, and the standard enthalpies of formation are obtained thereof: ΔH⁰_f (l or c) and ΔH^o_f (g) (in kJ mol^-1 for 1a= -308.40+/-0.52(1), -248.94+/-0.88; 1b= -343.48+/-0.72(1), -288.5+/-1.5; 1c= -267.4+/-1.3(1), -205.3+/-1.3; 1d = -343.8+/-2.1 (c), -261.9+/-2.2; 1e = -397.02+/-0.86 ( c), -311.3+/-1.2; 1f = -414.52+/-0.80 (1), -350.68+/-0.86; 2a = -564.8+/-2.4 (c), -467.1+/-2.5; 2b = -547.6+/-1.6 (c), -414.9+/-2.7; 2c = -717.1+/-7.5 (c), -587.0+/-8.0.The results are combined into values of two strain free group increments CH<20, C_Ph> = -59.7 and C<20, C_Ph, C> = -71.3 kJ mol^-1; and compared to the aliphatic series of acetals.