Structural studies of some push–pull N-arylbenzazoles

Abstract

X-Ray crystal structures, and calculated structures (at B3LYP/6-31G level) are reported for seven N-arylbenzazoles (two carbazoles, indoles and benzimidazoles, and one indazole) bearing electron withdrawing groups in the 2-position of the N-aryl ring. The structures are markedly non-planar by rotation around the N-aryl bond, with the substituent in most cases lying s-E in relation to the N-aryl bond; intermolecular electrostatic interactions in the crystal rationalise the two examples in which an s-Z conformation is observed. A large interplanar angle between the benzazole and the N-aryl planes is associated with a small interplanar angle between the planes of the N-aryl group and the substituent and vice versa.

Photoactivatable Fluorogens by Intramolecular C–H Insertion of Perfluoroaryl Azide

“…was used. 33 In the mono-substituted product, the large planar carbazole group is expected to be nearly perpendicular to the aryl ring due to steric repulsion. This strongly decreases the conjugative donation of the nonbonding electrons on nitrogen.…”

“…Interestingly, the mono-substituted product 8a was detected only in trace amount (Table ), even when a large excess of PFAA 6 (8 equiv.) was used . In the mono-substituted product, the large planar carbazole group is expected to be nearly perpendicular to the aryl ring due to steric repulsion.…”

ChemInform Abstract: Synthesis of Bis(indole) Alkaloids from Arundo donax: The Ynindole Diels—Alder Reaction, Conformational Chirality, and Absolute Stereochemistry.

“…[11,12] The C À N biaryl axis of 1-4 is flanked by three nonhydrogen substituents, and such substitution patterns often lead to chirality in biphenyls. [1] Moreover, typical C À N bonds which connect azoles with phenyl rings are shorter (1.419-1.430 ) [13] than CÀC bonds in biphenyls (1.482-1.507 ), [14] and would bring the large substituents closer, and could enhance steric effects.…”