The present study deals with the problem of the structural prediction of polypeptides starting from the amino acid sequence. To date it is still a problem in the field of protein folding and still needs to be solved, although it has been deeply investigated over the years. To predict the structure of a protein, is necessary to determine the backbone dihedral angles φ and ψ and, as reported from previous studies, the informations to fold a polypeptide chain in its three dimensional structure are contained in the amino acid sequence. To date, the type of informations contained in the sequence still need to be revealed. In this regard, the present study aims to furnish a theoretical method that allows the calculation of backbone dihedral angles, specifically the dihedral angles φ, starting from the amino acid sequence, attempting to furnish a possible explanation of the informations to fold a polypeptide, according to the amino acid sequence. The chemical interactions among the side chains of the amino acid residues were supposed to be the informations required to fold the polypeptide: these allow the development of mechanical forces which induce the twistings necessary to fold the polypeptide. This approach, already reported in literature and deepen in this study, showed are wrong. The method thus, aims to be a useful tool to investigate partially the structure of a polypeptide chain (since concerns only φ), predicting it starting from the amino acid sequence. It may represent a good starting point for future computational developments that focus on the prediction of protein structures starting from the amino acid sequence.