Trithiaazapentalene derivatives were prepared by the reaction of 2-alkylidene-4-oxothiazolidines with Lawesson's reagent. They are classified as two structurally different trithiaazapentalene compounds that have different contributions of monocyclic 1,2-dithiole and 1,2,4-dithiazole structures and degrees of aromaticity of the bicyclic trithiaazapentalene system. The electron-donating ability of substituents at the C(5) position of the trithiaazapentalene system is recognized as the main cause for changes in pi-Celectron distribution. This is the first complete study of substituent effects on the structure of trithiapentalenes. (C) 2013 Elsevier Ltd. All rights reserved.
Push-pull allenes-conjugation, (anti)aromaticity and quantification of the push-pull character
(2013)
Structures, H-1/C-13 chemical shifts, and pi electron distribution/conjugation of an experimentally available and theoretically completed set of push-pull allenes Acc(2)C=C=CDon(2) (Acc=F, CHO, CF3, C N; Don=t-Bu, OMe, OEt, SMe, SEt, NCH2R) have been computed at the OFT level of theory. Both orthogonal linear and orthogonal bent structures have been obtained. In the latter case the push-pull character could be quantified by the quotient method. The C-13 chemical shift of the central allene carbon atom C-2 and chemical shift differences Delta delta(C-1, C-2) and Delta delta(C-2, C-3) of allene carbon atoms proved to be a quantitative alternative. TSNMRS of ring-closed push-pull allenes have been computed in addition and were employed to identify polar, carbene-like and carbone-like canonical structures of these molecules.
