NMR investigation of hydrogen bonding and 1,3‐tautomerism in 2‐(2‐hydroxy‐5‐substituted‐aryl) benzimidazoles

Abstract

The 1,3-tautomerism associated with 2-(2-hydroxy-5-substituted-aryl)benzimidazoles was studied in different solvents. The effect of hydrogen bonding involving the hydroxyl group of the 2-aryl ring on the tautomerism was investigated using NMR spectroscopy. The influence of the solvent concentration on 2-(2-hydroxy-5-chloroaryl)benzimidazole was studied in acetone-d6 and DMSO-d6.

Efficient combination of task‐specific ionic liquid and microwave dielectric heating applied to synthesis of a large variety of nitrones

“…It shows that yields (>92% yields) were satisfactory under microwave irradiation conditions. On the other hand, the relatively hindered aldehydes, i.e., 2-naphtylaldehyde, 2,3-dihydroxybenzaldehyde, and 2-hydroxy-5-methoxybenzaldehyde also led to the good yields of the related nitrones (entries 9,15,19). The reactions worked well with aromatic aldehydes.…”

“…Microwave irradiation has also been used for the synthesis of α-(5-substituted-2-hydroxyaryl)-N-aryl nitrone [19]. Recently, Bortolini and Maiuolo reported the synthesis of nucleoside derivatives by the microwave-assisted 1,3-cycloaddition reaction of vinyl nucleobases with nitrones under solvent-free conditions [20].…”

Synthesis and voltammetric detection of 1H-benzimidazole derivatives on the interaction with DNA

“…1 H NMR results were interpreted in experimental section. The aromatic proton signals of p-hydroxyphenyl substituent at position 2-of 1H-benzimidazole ring were observed within prospective chemical shift values and divisions as 1,4-disubstituted benzene system (as two protons doublets H-3′, H-5′ at δ 6.87-6.95 and H-2′, H-6′ at δ 7.90-7.98) while the hydrogen atoms at positions 4-and 7-were not detected at the prospective divisions (32). The compounds substituted with the terminal of ethoxy chain at position 4-of phenyl group gave rise to similar chemical shift values and divisions at the ring of the benzimidazole nucleus as 1-3.…”

“…The lack of the signal belonging to 3a, 4, 7 and 7a C in 13 C NMR are noteworthy that may suggest a proton exchange due to 1, 3-tautomerization (32). All the other aliphatic and aromatic carbons were observed at expected regions.…”

Simple, Mild, and Highly Efficient Synthesis of 2-Substituted Benzimidazoles and Bisbenzimidazoles

“…41,42 The NH protons of compounds containing 1H-benzimidazole ring appear as broad singlets at 12.0-13.3 ppm. Because of the 1,3-tautomerisation 41 3a/7a, 4/7, and 5/6 positions of the unsubstituted benzimidazoles are equivalent and generally appears at the same region in the 1 H-and 13 C-NMR spectra.…”