Tautomeric Equilibria in Solutions of 2-Phenacylbenzimidazoles

Table 2

Content of the K form (%) (solutions in DMSO-d₆).

Compound	Substituent R	[K] (%)
2a	p-OCH3	49.2 (49.5); 50 [4]; 52 [5]
2b	p-CH3	32.0 (33.6)
2c	m-CH3	23.1 (24.2)
2d	H	21.9; 20 [4]; 21[5, 7]
2e	p-F	21.9
2f	p-Cl	13.0; 12 [5]
2g	p-Br	15.3
2h	m-F	13.0
2i	p-NO2	3.9; 2 [4]; 4 [5]; 0 [8]

Based on integrals of the H10 signals (present paper). Literature data collected from DMSO-d₆ solutions. Values in parentheses are based on integrals of the substituent protons (CH₃, 3.91 ppm for 2a (form K) and 3.87ppm for 2a (form O), 2.51 ppm for 2b (form K) and 2.37 ppm for 2b (form O), 2.51 ppm for 2c (form K) and 2.40 ppm for 2c (form O)).