The specific position of a group in the molecule has been considered, and a group vector space method has been developed to estimate the normal boiling temperature and enthalpy of vaporization of organic compounds. Expressions for the boiling temperature T-b and enthalpy of vaporization Delta(vap)H(T-b) have been established, and numeric values of relative group parameters have been obtained. The average percent deviations of the estimation of T-b and Delta(vap)H(T-b) are 1.5 and 1.0, respectively, which show that the present method demonstrates significant improvement in the ability to predict the above properties, compared to that of conventional group methods.