Chiroptical structure‐property relations in cyclo[18]carbon and its in silico hydrogenation products

Abstract

The anisotropy of the optical activity of cyclo[18]carbon (C ), fully hydrogenated C (C H ), and 26 hydrogenated compounds of intermediate composition, C H , n = 1,2…17, were computed. These compounds were selected because they resemble loops of wire. The maximum gyration for acetylenic and cumulenic subgroups of compounds was linearly proportional to the product of the geometric area over which the charge can circulate, multiplied by the largest separation between carbon atoms on opposing sides of the loops. These geometric quantities can be likened to transition magnetic dipole moments and transition electric dipole moments, respectively, that can be generated in electronic excitations and which contribute in the main to nonresonant optical activity. The correlation between a computed geometric product of distance and area, and a quantum chemical property, establishes that chiroptical structure-activity relationships can be well established for judiciously chosen series of comparatively large compounds.

Cyclo[18]carbon: Insight into Electronic Structure, Aromaticity, and Surface Coupling

“…Numerous electronic structure calculations of cyclo [18]carbon molecule have been carried out at the different levels of theory including the HF, 18,20 SCF, [21][22][23] MCSCF, 24 MP2, 21,22 DFT, 19,21,[25][26][27][28][29][30][31][32] quantum Monte Carlo (QMC) 24 and CCSD 23,29 levels. Surprisingly, only the HF, QMC and CCSD methods yield the polyyne structure that experimentally has been observed in high-resolution atomic force microscopy (AFM) measurements of cyclo [18]carbon adsorbed on bilayer NaCl on Cu(111) surface at the temperature of 5 K. 16 Most of the common DFT functionals 19,21,[25][26][27][28][29][30][31][32] (B3LYP, BLYP, PBE0, etc.) as well as MP2 calculations 21 yield the nonbond-length alternating cumulene structure of cyclo [18]carbon.…”

“…Numerous electronic structure calculations of the cyclo[18]­carbon molecule have been carried out at the different levels of theory, including the HF, , SCF, − MCSCF, MP2, , DFT, ,,− quantum Monte Carlo (QMC), and CCSD , levels. Surprisingly, only the HF, QMC, and CCSD methods yield the polyyne structure that experimentally has been observed in high-resolution atomic force microscopy (AFM) measurements of cyclo[18]carbon adsorbed on bilayer NaCl on a Cu(111) surface at a temperature of 5 K .…”

“…Surprisingly, only the HF, QMC, and CCSD methods yield the polyyne structure that experimentally has been observed in high-resolution atomic force microscopy (AFM) measurements of cyclo[18]carbon adsorbed on bilayer NaCl on a Cu(111) surface at a temperature of 5 K . Most of the common DFT functionals ,,− (B3LYP, BLYP, PBE0, etc.) as well as MP2 calculations yield the non-bond-length alternating cumulene structure of cyclo[18]­carbon.…”

Configuration Space Analysis of the Specific Rotation of Helicenes

“…This work showed that the large [α] ω of (1 S ,4 S )-norbornenone is due to electron delocalization between the CO and CC chromophores . Kahr and co-workers extended the analysis of optical activity to include nonchiral molecules through a simple and effective Hückel theory decomposition. , Wiberg examined the effect on [α] ω of the rotation of the torsional angle of terminally substituted 1,4-pentadiene (CC to CX interactions, where X = C, O, NH, and S) and found a dependence on the electronegativity of X. , We have also introduced a method of decomposing [α] ω in terms of transition electric and magnetic dipole contributions, called the S̃ k method (discussed in Section ). , We showed that a limited number of orbital transitions can be used to describe [α] ω for molecules with strong chromophoric groups and that changes in [α] ω due to conformational flexibility are dominated by a small number of transitions, thus simplifying the interpretation of the structure–property relationship.…”

“…18 Kahr and co-workers extended the analysis of optical activity to include nonchiral molecules through a simple and effective Huckel theory decomposition. 19,20 Wiberg examined the effect on [α] ω of the rotation of the torsional angle of terminally substituted 1,4-pentadiene (CC to CX interactions, where X = C, O, NH, and S) and found a dependence on the electronegativity of X. 21,22 We have also introduced a method of decomposing [α] ω in terms of transition electric and magnetic dipole contributions, called the S ̃k method (discussed in Section 2).…”