Aromaticity and antiaromaticity in monoheterocyclic three‐membered rings: Application of natural bond orbital theory

Abstract

Using natural bond orbital theory, aromatic stabilization energies (NBO-ASEs) were calculated for neutral and cationic monoheterocyclic three-membered rings C 2 H 2 X(R) n (X = group 14-17 elements of rows 3-5; R = F, H or SiH 3 ;and n = 0-2). Generally, there was a decrease in the (anti)aromatic nature of the molecule moving down the group as either the stabilizing orbital overlap (aromaticity) or destabilizing orbital interactions (antiaromaticity) were reduced due to larger atoms inducing longer bonds. (Anti)aromatic trends were supported with dissected nucleus independent chemical shift NICS(0) π,zz values (R 2 = 0.94) and also by comparison of NBO-ASEs to literature values for a selection of larger systems including benzene, cyclobutadiene, and the cyclopentadienyl anion. Comparisons are made to other studies that have used a range of approaches to study (anti)aromaticity in some of these molecules, and it was found that non-dissected NICS values and homodesmotic equations often gave significantly overestimated if not misleading results.

Neutral Three Membered 2π Aromatic Beryllacycle having σ hole

“…Apart from classical cyclopropenyl cation, a large number of heteroatom substituted three-membered aromatic heterocycles were reported, such as B 3 H 3 2À , Al 3 H 3 2À , Si 2 BH 3 , etc. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The bonding and aromaticity of 3-membered heteroaromatic cycles involving group 14 elements were extensively studied by Frenking and co-workers. [16] A large number of theoretical studies suggest that the replacement of À CH fragment by heavier heteroatom hydride results in hydrogen bridged structure with lone pair on a heavier atom as the most stable structure.…”

“…[1][2][3][4][5][6][7][8][9][10] There are many studies reported on neutral three-membered main group hydrides isoelectronic to cyclopropenyl cation. [1][2][3][4][11][12][13][14] The replacement of one of the + CH in classical cyclopropenyl cation by isoelectronic species main group fragments was well studied. The replacement by BH gives a neutral boron analogue of cyclopropenyl cation borirene, C 2 BH 3 (Scheme 1, II).…”

“…[12] The other neutral 2π aromatic three-membered compounds are BSi 2 N, SiB 2 H 4 , etc. [1][2][3][4][11][12][13][14] These compounds have 14 valence electrons, out of which 12 and 2 electrons are part of σ and π skeleton, respectively. The replacement of the BH group in compound II by beryllium results in compound III with 12 valence electrons.…”