الفهرس 
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Abstract
This thesis includes :1-Study the polarographic and spectrophotometric acidity of one of the mostly biologically important compounds, namely 2-thiouracil (I) and its 5-phenyl azo-substituted derivatives (IIa-f),polarographic runs were carried in buffer solution of wide pH range (pH ~2-12).2-The polarograms of compounds IIa-b revealed the predominance of one reduction wave at the DME in the accessible pH range.3-Study the effect of pH on E1/2 and limiting current il for compound IIa, As disclosed from the plot a linear correlation.4-The diffusion nature of the wave was tested by examining the effect of time and concentration at different pH. The measurement sustains the diffusion-controlled nature of the wave.5-The irreversibility nature of the wave was a scertained from cyclic voltammetry carried at different pH.6-The polarographic behaviour of compounds IIb-d was generally identical with that of the parent compound IIa.7-The m-NO2 (IIe) and p-NO2 (IIf) derivatives displayed additional reduction wave (b) at more negative potential corresponding to reduction of their nitro group.8-The acid dissociation constant (pKa) of compounds (IIa-f) were determined spectrophotometrically.9-Calculated pKa values for compounds IIa-f ranged from 7.2-9.352.10-Linear free energy relationship (LFER) was tested through E1/2 and pKa at different pH with Hammett’s σ constant. plots of E1/2 and pKa & σ reflect reasonable linearity with +P~2.