A mndo study of 3-, 5-, 7- and 9-membered carbocyclic, completely conjugated, planar carbenes and their nonplanar isomers

Inner-Phase Stabilization of Reactive Intermediates

“…This interpretation was recently questioned by Waali et al [68] On the basis of their semiempirical calculations, which show a strong similarity between the HOMO of cycloheptatetraene and that of cycloheptatrienylidene, they believe that in all the reactions discussed above, cycloheptatetraene is the reacting species. The through-shell reaction studies with bulk-phase methanol performed in this laboratory clearly demonstrate that this is only partially true.…”

Singlet–triplet energy separations in divalent five-membered cyclic conjugated C5H3X, C4H3SiX, C4H3GeX, C4H3SnX, and C4H3PbX (X = H, F, Cl, and Br)

“…These divalent structures were formerly described in terms of the Huckel 4n + 2 rule [3]. However, semi-empirical studies found most of these singlets, planar, cyclic conjugated carbenes not to be energy minima, suggesting non-planar isomers to be considered [4]. Arduengo and co-workers [5] reported the isolation of the stable cyclic conjugated carbene, 1,3-di(1-adamantyl)imidazol-2-ylidene.…”

In search of triplet ground state GeCNX germylenes (X=H, F, Cl, and Br): An ab initio and DFT study

“…One of the most interesting organic species found in the space is C 3 H 2 . It has become the topic of a large number of theoretical researches [3][4][5][6][7][8][9][10][11][12][13]. This is in part due to the economy of the theoretical work with the small molecules.…”

“…Moreover, singlet cyclopropenylidene is predicted to be 28 kcal/mol more stable than triplet cyclopropenylidene [4]. Both carbenic singlet cyclopropenylidene electrons are predicted to occupy the system (r 2 ) in its ground state [9]. Recently, many workers have addressed interesting questions of how the presence of substituents affect the relative stabilities of different C 3 H 2 isomers.…”