Yvon Lambert

Distributions electroniques et effets chimiques: XXVIII. Etude théorique et expérimentale du tricyclo[4.4.0.03,8] decane (“twistane”)

Abstract The atomization energy, Δ E a *, of tricyclo[4.4.0.0 3,8 ]decane (“twistane”) in its hypothetical vibrationless state at 0 K has been calculated from the equation ϵ ij = ϵ ij 0 + a ij Δ q i + a ji Δ q j , which gives the energy contribution of the bond ij in terms of the variations in net atomic charges Δ q i and Δ q j with respect to the populations of atoms i and j of a reference bond with energy ϵ ij 0 . Using theoretical a ij 0 coefficients we obtain Δ E a * (twistane) = 2679.0 kcal mol −1 . The comparison with its structural isomer adamantane reveals a gain in stability (1.53 kcal mol −1 ) for the 16 CH bonds in twistane and a loss in stability of its carbon skeleton (10.69 kcal mol −1 ) due to lower electron populations of the carbon atoms in twistane. Assuming similar vibrational energies for twistane and adamantane, the calculated enthalpy of formation is Δ H f 0 (gas, 298.15) = −21.6 kcal mol −1 for twistane, with an estimated error of ⩽ 0.3 kcal mol −1 . The measured heat of combustion is −1451.3 kcal mol −1 for twistane. Moreover, sublimation pressures measured by the Knudsen effusion method between 0.9 and 26°C give an enthalpy of sublimation of 14.1 kcal mol −1 . Finally, the experimental enthalpy of formation of twistane amounts to Δ H f 0 (gas, 298.15) = −21.6 ± 0.4 kcal mol −1 .