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Structural properties and 13 C chemical shifts of bis‐ and tris(2‐thienyl)methinium and related cations: a combined theoretical and experimental study
Author(s) -
Fabian Jürgen,
Hartmann Horst,
Noack Antje
Publication year - 2003
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.573
Subject(s) - chemistry , density functional theory , chemical shift , basis set , computational chemistry , conformational isomerism , zindo , tris , isomerization , molecule , crystallography , organic chemistry , biochemistry , catalysis
Abstract The molecular structure of the parent bis‐ and tris(2‐thienyl)methinium ions were studied by first‐principles methods (second‐order Møller–Plesset many‐body perturbation theory and density functional theory). In contrast to bis(2‐thienyl)methinium, tris(2‐thienyl)methinium is non‐planar with torsion angles between the thienyl groups and the central plane of about 30°. The calculations on tris(2‐thienyl)methinium resulted in two almost isoenergetic conformers with barriers to isomerization less than 10 kcal mol −1 (1 kcal = 4.184 kJ). In order to discuss the 13 C chemical shifts of Crystal Violet and of heteroanalogous compounds with thienyl‐2‐, with 5‐amino‐thienyl‐2‐, with 5‐methylmercapto‐thienyl‐2‐ and with 5‐amino‐1,3‐thiazolyl‐2‐heteroaryl groups, the structure was optimized at the DFT B3‐LYP/6–31G(d) level and the chemical shifts were calculated at the DFT‐GIAO/6–311 + G(2d,p) level of theory. In general, the experimental chemical shifts correlate very well with the experimental values. The lowest energy electronic transitions in the UV–VIS region were calculated by time‐dependent density functional response theory (TD‐DFRT) using the DFT B3‐LYP/6–31 + G(d) basis set. For cationic dyes the agreement between the results of TD‐DFRT calculations and experiment was less good than for neutral sulfur‐containing compounds. Semiempirical calculations (PPP, ZINDO/S) are better in that case and are more efficient. Copyright © 2002 Wiley & Sons, Ltd.