NMR investigations on benzheteroazoles. 2—NMR investigations of N‐acylated 2‐aminobenzimidazoles

Abstract

The "C NMR chemical shifts of 74 N-acylated 2-aminohenzimidazoles were determined and assigned. The chemical shifts are discussed as a function of electronic and spatial substituent effects. Line broadening for certain C signals are traced to prototropy at N-1 and N-3, and N-3 and N,,.

Versatile behavior of 2-guanidinobenzimidazole nitrogen atoms toward protonation, coordination and methylation

“…[ These compounds were prepared directly in three resonance tubes of high resolution and 5 mm diameter as reported below. [ 3,. A solution of 250 mg (1.43 mmol) of 1a in 0.5 mL of H 2 SO 4 (97%) was prepared.…”

“…IR m cm [ acetate (3). To a hot solution of 175 mg (1 mmol) of 1a in 15 mL of methanol was added a solution of 268 mg (1 mmol of Mn(CH 3 COO) 3 C,47.43;N,27.65;H,5.92;found: C,47.50;N,28.04;H, [bis ] 6. A solution of 1.835 g (5 mmol) of NiCO 3 2Ni(OH) 2 4H 2 O in 60 mL of hot water was added to a hot solution of 876.0 mg (5 mmol) of 1a in 40 mL of methanol.…”

“…A beige solid was obtained, 168 mg (100%), mp 219-221ЊC. IR m cm [ acetate (3). To a hot solution of 175 mg (1 mmol) of 1a in 15 mL of methanol was added a solution of 268 mg (1 mmol of Mn(CH 3 COO) 3 C,47.43;N,27.65;H,5.92;found: C,47.50;N,28.04;H, [bis ] 6.…”

“…The molecule may present several tautomers and conformers. Its structure and dynamical behavior have been studied in solution by 1 H [2], 13 C [2,3], and 15 N [4] NMR spectroscopy, and the equivalent conformers I and II were suggested as the principal contributors to the molecular structure of 1a in solution. These are in equilibrium and stabilized by intramolecular hydrogen bondings [2].…”

In Search of the Weak, Six‐Membered Intramolecular Hydrogen Bond in the Solution and Solid States of Guanidinobenzimidazole

“…The chemical literature supports the N10-dehydrotautomer of 1 drawn in Figure 1 versus N12-or N13-dehydrotautomers. [11,12] The intramolecular hydrogen bond, S(6), Etter's notation, [13] in neutral 1 should be weak because of the non-optimal relative positions of the hydrogen-bond donor guanidine NH and the imidazole hydrogen-bond acceptor.…”