... 6.3 (d, J = 21.5 Hz, 1H), 7.4 (dd, J1 = 22.0, J2 = 22.0 Hz, 1H), 8.0 (s, 1H) ppm. ... depending on the position and nature of the substituents on the ring.(26) The N– atom involves in the formation of keto–enol tautomerism by exchanging the neighboring hydroxyl proton at C-2 position ...