Carbo-Cages: A Computational Study

Abstract

Inspired by their geometrical perfection, intrinsic beauty, and particular properties of polyhedranes, a series of carbo-cages is proposed in silico via density functional theory computations. The insertion of alkynyl units into the C-C bonds of polyhedranes results in a drastic lowering of the structural strain. The induced magnetic field shows a significant delocalization around the three-membered rings. For larger rings, the response is paratropic or close to zero, suggesting a nonaromatic behavior. In the carbo-counterparts, the values of the magnetic response are shifted with respect to their parent compounds, but the aromatic/nonaromatic character remains unaltered. Finally, Born-Oppenheimer molecular dynamics simulations at 900 K do not show any drastic structural changes up to 10 ps. In the particular case of a carbo-prismane, no structural change is perceived until 2400 K. Therefore, although carbo-cages have enthalpies of formation 1 order of magnitude higher than those of their parent compounds, their future preparation and isolation should not be discarded, because the systems are kinetically stable, explaining why the similar systems like carbo-cubane have already been synthesized.

The Thermochemistry of Cubane 50 Years after Its Synthesis: A High-Level Theoretical Study of Cubane and Its Derivatives

“…Still today the 1966 gas-phase enthalpy of formation value for cubane is used as a reference for the assessment of capabilities of modern quantum chemistry methods. For instance, a value of 644.3 kJ mol –1 (some 40 kJ mol –1 higher than the value determined in the present work) was very recently proposed …”

“…For instance, a value of 644.3 kJ mol −1 (some 40 kJ mol −1 higher than the value determined in the present work) was very recently proposed. 91 The bond dissociation enthalpies (BDEs), proton affinities (PAs), electron affinities (EAs), gas-phase acidities (ΔH acid ), and appearance energies (AEs) determined from theoretical data computed with W1-F12 were found to be in good agreement with the available experimental data. Following DePuy et al 78 and Gronert, 85 the trends for electron affinities and gas-phase acidities were rationalized in terms of the stabilization−destabilization of the resulting anion due to α methyl substituents, as well as the stabilizing effect of β methyl groups.…”

Paradigms and paradoxes. Tetrahedral units: dodecahedral super-structures

“…That is, each C-C bond between 2 adamantyl building blocks is replaced by an acetylene bridge where the dashed lines on the left & right summarily indicate an adamantane cage. Indeed just such a replacement has been suggested previously, in related contexts: in graphene [14], in cubane [15], in different polyhedranes [16,17] and miscellaneous other carbo-cages [18] (including adamantane). Basically the total stress is reduced because the strain is spread out over3 bonds & 4 bond angles, rather than 1 bond & 2 bond angles, so that with the stress energy quadratic in the strain, the resultant total stress energy should be roughly half as big (from comparing…”

“…That is, each C-C bond between 2 adamantyl building blocks is replaced by an acetylene bridge where the dashed lines on the left & right summarily indicate an adamantane cage. Indeed just such a replacement has been suggested previously, in related contexts: in graphene [14], in cubane [15], in different polyhedranes [16,17] and miscellaneous other carbo-cages [18] (including adamantane).…”

Testing the effectiveness of the isoelectronic substitution principle through the transformation of aromatic osmathiophene derivatives into their inorganic analogues

“…[46][47] In all cases, five-membered rings (5-MRs) were placed in the xy plane with the geometrical center coinciding at the origin of the Cartesian coordinates. [64][65][66][67] or where NICSiso interpretation is not clear.…”