The enthalpies of formation of ethylcyclobutane, methylenecyclobutane, and 1,1-dimethylcyclopropane.
The enthalpies of combusion of ethylcyclobutane, methylenecyclobutane, and 1,1-dimethylcyclopropane were measured by oxygen-bomb combustion calorimetry. The following values are reported for the standard enthalpy of combustion ^hc deg. (298.15 K)/kcalth mol-1 of these compounds in the liquid state: ethylcyclobutane, -(960.11 +/-0.16); Methylenecyclobutane, -(765.95 +/-0.12); 1,1-Dimethylcyclopropane, -(803.86 +/-0.17. The enthalpy of vaporization of methylenecyclobutane was derived from vapor pressure measurements, and enthalpies of vaporization of ethylcyclobutane and 1,1-dimethylcyclopropane were estimated. Values of the enthalpy of formation in the liquid and gaseous states were derived for all three compounds. Ring-strain energy was estimated. Some regularities and irregularities in the accepted values of enthalpies of combustion of the alkylcyclopropanes and alkylcyclobutanes indicate an error in a previous determination of the enthalpy of formation of methylcyclobutane.