A FORTRAN (77) program, includes the NINDO/3-Force method, was applide to calculate the 3N-6 fundamental vibrational frequencies, IR absorption intensities, and the eigenvectors coefficients for the following substituted phenyl derivatives:-PhF, PhCl, PhCN, PhNO2, PhOH, PhSH, PhNO, PhOCH3 , PhCOCH2 ,
PhCH3 1,2-dimethyl, 1,3-dimethyl, and 1,4-dimethylbenzene. Also, a complete normal coordinate analysis was done to each one of the vibrational frequencies and to all the above derivatives. The HINDO/3-Forces method was then extended to include atoms of third row elements and tested with PhCl and PhSH. All calculations
to obtain the 3N-6 fundamental vibrational frequencies was done to displacements from equilibrium configuration around ± 0.001 nm. The eigenvectors were used in calculating the APP values, IR absorption intensities, and in doing the graphical representation of each normal mode. Calculated results compared very well with experimental and other theoretical results. A correlation was found between the symmetric bending vibration of the methyl substituent group and the electronegativity of the atom adjacent to this group. For PhCOCH3 , 1,2-dimethylbenzene, and PHOCH3 derivatives, the symmetric methyl bending vibration was of the values 1324, 1377, and 1401 cm-¹ respectively.