Ground states of conjugated molecules. XX. SCF MO treatment of compounds containing bivalent sulfur

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

“…In contrast, the flattened transition structures for ring inversion of thiepine and phosphepine are indeed highly antiaromatic planar 8π-electron systems, with positive NICS(1) values of 19.3 [ 47 ] and 6.4 ppm [ 7 ], respectively. The inherent instability of thiepine ( 5 ) has been attributed to this effect [ 51 – 52 ].…”

“…By changing to more polar solvents, the oxepine isomerization equilibrium shifts further toward benzene oxide (more positive Δ G ), suggesting that benzene oxide has the larger dipole moment. Methyl substitution at the 2- and 7-positions reverses the stability order, rendering the oxepine as the energetically favoured isomer due to the destabilizing eclipsing of the two methyl groups in benzene oxide ( 4 ) [ 38 , 40 , 51 ]. Thus, in contrast to the cycloheptatriene–norcaradiene ( 1 – 2 ) pair, the equilibrium constant for oxepine ( 3 ) and bicyclic benzene oxide ( 4 ) varies widely with solvent polarity and to some extent with temperature and substituents, making it possible to work with solutions highly enriched with either one or the other isomer [ 38 , 55 ].…”

Recent studies of the synthesis, functionalization, optoelectronic properties and applications of dibenzophospholes

“…Most of the reactions started from the tertiary phosphine-borane 93 and a variety of odibromobenzenes to simultaneously create an aryl-aryl bond and the ve-membered ring of the dibenzophosphole moiety in 15-60% yields (Scheme 20). 36 The use of P-modied boranes 105 in which R 3 or R 4 ¼ Ph has been replaced by tert-butyl (t-Bu), cyclohexyl (Cy) or orthoanisyl (o-An) (2-MeOC 6 H 4 ) groups did not improve yields of these reactions (27-44%). Interestingly, in the case of 105 (R 3 ¼ Ph, R 4 ¼ o-An), preferential P-o-An cleavage occurred to give 109 (R 3 ¼ Ph) in 44% yield (Scheme 21).…”

“…A disadvantage of the systems containing aromatic building blocks has oen been a too high degree of aromaticity, which inhibits an easy electron delocalization along the conjugated rings when in an oxidized state. [2][3][4] Therefore, this type of molecular system requires a benecial incorporation of heteroaromatic rings, for example vemembered pyrrole, thiophene or furan, possessing lower aromatic stabilization energies (ASE calc : 20.57, 18.57, 14.77 kcal mol À1 , respectively) than a benzene ring. The aromatic character of the phosphole ring (ASE calc ¼ 3.2 kcal mol À1 ) is relatively low due to the pyramidal geometry of the phosphorus atom.…”

Influence of heterocycle substitution in π-functional materials for organic photovoltaics

“…Benzene aromaticity, having a greater aromatic resonance energy than thiophene (1.56 vs 1.26 eV, respectively), is preferred over thiophene aromaticity. 59,60 This preference allows the main chain of PITN to favor the quinoid form to maintain benzene aromaticity, narrowing the bandgap.…”