Structural properties and 13C chemical shifts of bis‐ and tris(2‐thienyl)methinium and related cations: a combined theoretical and experimental study

Medientyp: E-Artikel
Titel: Structural properties and 13C chemical shifts of bis‐ and tris(2‐thienyl)methinium and related cations: a combined theoretical and experimental study
Beteiligte: Fabian, Jürgen; Hartmann, Horst; Noack, Antje
Erschienen: Wiley, 2003
Erschienen in: Journal of Physical Organic Chemistry
Sprache: Englisch
DOI: 10.1002/poc.573
ISSN: 0894-3230; 1099-1395
Schlagwörter: Organic Chemistry ; Physical and Theoretical Chemistry
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Beschreibung: <jats:title>Abstract</jats:title><jats:p>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<jats:sup>−1</jats:sup> (1 kcal = 4.184 kJ). In order to discuss the <jats:sup>13</jats:sup>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.</jats:p>

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