The infrared absorption of electrochemically synthesized polyaniline is measured in situ during the electrochemical redox processes in non aqeous electrolytes with Fourier Transform (FTIR) technique. The first oxidation process is associated with a strong increase in the background absorption in addition to vibrational changes due to the benzenoid-semiquinoid transition in the ring structure and loss of protons bound to the nitrogen atoms. In the second oxidation process intercalation of anions occurs, the background absorption decreases and quinoid ring bands appear. From these results and neutron activation analysis of anions in the polymer we derived a structural model of polyaniline, which explains the changes in the two redox processes.