If the pK_b value of p-nitroaniline is 13, predict the pK_b value of its ortho isomer?

14.22

The -NO₂ group is an electron withdrawing group and has a weakening effect on the basicity of anilines. Its presence at para position will be more influencing than at meta, but less weakening than at ortho position. This anomaly is due to a complex ortho effect (stearic and electronic reasons). Hence o-nitroaniline is a weaker base and has a higher pK_b value than p-nitroaniline.