Issue 2, 2019, Issue in Progress

Experimental and theoretical investigation of intramolecular cooperativity in cyclic benzene trimer motif

Abstract

A series of new symmetrical tripodal molecules 1a–4b with a central benzene scaffold substituted with methyl/ethyl groups and three benzimidazolyl units having a bithiophene/biphenyl/5-alkylthiophene motif at the 2-position via a –CH2– unit were synthesized and characterized by elemental analysis, HR-MS, and NMR spectroscopy. NMR spectral data reveal that all molecules adopt a cyclic benzene trimer (CBT) using three benzimidazolyl units. Intramolecular cooperative edge-to-face C–H⋯π interactions stabilize the CBT motif in solution and are strong in ethyl substituted molecules (1b–4b) compared to methyl substituted (1a–4a) ones. However, the strength of the CBT unit in the tripodal molecule is independent of the length of the substituent at the 2-position of the benzimidazolyl unit. The relative 1H NMR chemical shift calculated at the MPW1PW91/6-311+G(d,p) level of theory corroborates the experimental values, and the calculations predict the distribution of the structures into syn isomers. The relative change in the NMR chemical shift is justified by the relative change in the magnitude of the (3,+3) critical point (CP) in the molecular electrostatic potential (MESP) topography. Also, a linear correlation of the intramolecular C–H⋯π interactions evaluated at M062X/6-311+G(d,p) with the relative NMR chemical shift suggest the latter as a measure of intramolecular cooperativity.

Graphical abstract: Experimental and theoretical investigation of intramolecular cooperativity in cyclic benzene trimer motif

Supplementary files

Article information

Article type
Paper
Submitted
07 Aug 2018
Accepted
18 Dec 2018
First published
04 Jan 2019
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2019,9, 753-760

Experimental and theoretical investigation of intramolecular cooperativity in cyclic benzene trimer motif

C. K. Kumar, S. Deval Sathiyashivan, D. T. Masram, K. V. J. Jose and M. Sathiyendiran, RSC Adv., 2019, 9, 753 DOI: 10.1039/C8RA06647G

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