The13C NMR, UV and IR absorption spectra of 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-pyridinedicarboxylic acids were recorded and their spectral parameters were assigned. The influence of electronic properties of the substituents on the direction of the chemical shifts is discussed. The influence of substituents in the molecule on λmax and emax of the UV-spectral band is disscused. Analizing13C NMR, UV, and IR absorption spectra it was found that there is a disturbance of mutual electronic interaction of substituents by a steric ortho effect. This effect is reflected in paramagnetism of the carboxyl group, the value of the correlation coefficient, deformation C−O stretching bands, and the decrease in the intensity of the CT band.