GEMINAL SUBSTITUENT EFFECTS .9. STANDARD ENTHALPIES OF FORMATION AND STRAIN FREE INCREMENTS OF BRANCHED ESTERS AND ETHERS

The standard enthapies of combustion Delta(c)H((liq.))degrees of the b ranched esters 1,2 and ethers 3 were measured calorimetrically. The en thalpies of vaporisation Delta(v)H degrees of 1-3 were obtained from t he temperature function of the vapor pressure in a flow system. The fo llowing results are obtained from these data: Delta(f)H((liq.))degrees Delta(v)H degrees for 1a: -556.1+/-1.6, 44.39+/-0.16; 1b: -587.4+/-1. 6, 44.49+/-0.39; 1c: -609.5+/-1.2, 50.57+/-0.51; 1d: -614.7+/-1.5, 48. 39+/-0.18; 1e: -616.4+/-1.0, 50.39+/-0.34; 2a: -, 51.73+/-0.23; 2b: -6 05.7+/-2.7, 60.04+/-0.63; 2c: -554.5+/-1.3, -; 2d: -581.8+/-1.5, 42.81 +/-0.34; 2e: -624.78+/-0.98, 50.84+/-0.57; 3a: -409.1+/-2.0, 40.94+/-0 .30; 3b: -428.34+/-0.90, 46.14+/-0.25; 3c: -406.7+/-1.5, 44.90+/-0.50; 3d: -, 53.13+/-0.19 kJ mol(-1). From Delta(f)H((gas))degrees of 1-3 a nd a critical choice from known data were derived new values of group increments for the estimation of standard enthalpies of formation of e sters CO2 [2C] -327.05, CH3[CO2]-42.05, CH2[CO2, C]-17.40, CH[CO2, 2C] -7.40, C[CO2, 3C] 4.51, CH30 [O] -42.05, CH20[O, C] -33.76, CH0[O, 2C ] - 31.30, C-0[O, 3C] -20.20 and of ethers O[2C] -99.23, CH3[O] -42.05 , CH2[O, C] -33.06, CH[O, 2C] - 25.64, C[O, 3C] -18.16, Ph[O] 72.02 kJ mol(-1).