The paper is devoted to the problems of synthesis reaction physics of light elements. In this area, experimental data and models of nuclei interaction processes created on their basis play an important role. Quite accurate experimental data on the interaction cross sections have been accumulated, approximation formulas have been obtained that describe dependences of the cross sections of a number of reactions on nuclear collision energy. However, creation of models that describe in detail the progress of reactions encounters such difficulties as complexity to describe problems with many variables, difficulties of obtaining reliable experimental data on the scale of nuclear interactions. This paper provides an attempt to describe the synthesis processes in the D−D, D−Т, D−3He, Т−Т и 3He−3He reactions based on the possibility to separate interacting nuclei into quasi-free fragments. Three leading fragments in these reactions were revealed. The calculations of the cross sections based on these representations gave interesting results. Areas of action of nuclear forces in these reactions were determined.