Applicability of Baird’s Rule for In-Plane Aromaticity

The concept of aromaticity is essential for chemists to understand the nature of many chemical substances. “In-plane” aromaticity is a unique type of aromaticity found in some π-conjugated systems consisting of radially oriented p-orbitals. Although in-plane aromaticity has been theoretically predicted about 40 years ago, its intrinsic properties are much less well understood than those of conventional Hückel aromatic systems with perpendicularly oriented p-orbitals because of lack of available examples of in-plane aromatic molecules. Here we demonstrate, from both theoretical and experimental aspects, that in-plane aromaticity of cycloparaphenylenes is reversed upon excitation to the lowest triplet state. In-plane non-aromatic neutral forms with a 4N-electron system and in-plane aromatic dications with a 4N+2-electron system turn out to be aromatic and anti-aromatic, respectively, indicating that Baird’s rule holds for the in-plane aromatic system. Armchair carbon nanotube fragments based on the cycloparaphenylene were also found to follow Baird’s rule from a magnetic viewpoint.<br>

Applicability of Baird’s Rule for In-Plane Aromaticity

The concept of aromaticity is essential for chemists to understand the nature of many chemical substances. “In-plane” aromaticity is a unique type of aromaticity found in some π-conjugated systems consisting of radially oriented p-orbitals. Although in-plane aromaticity has been theoretically predicted about 40 years ago, its intrinsic properties are much less well understood than those of conventional Hückel aromatic systems with perpendicularly oriented p-orbitals because of lack of available examples of in-plane aromatic molecules. Here we demonstrate, from both theoretical and experimental aspects, that in-plane aromaticity of cycloparaphenylenes is reversed upon excitation to the lowest triplet state. In-plane non-aromatic neutral forms with a 4N-electron system and in-plane aromatic dications with a 4N+2-electron system turn out to be aromatic and anti-aromatic, respectively, indicating that Baird’s rule holds for the in-plane aromatic system. Armchair carbon nanotube fragments based on the cycloparaphenylene were also found to follow Baird’s rule from a magnetic viewpoint.<br>

A tris-spiro metalla-aromatic system featuring Craig-Möbius aromaticity

As aromaticity is one of the most fundamental concepts in chemistry, the construction of aromatic systems has long been an important subject. Herein, we report the synthesis and characterization of a tris-spiroaromatic complex, hexalithio spiro vanadacycle 2. The delocalization of the four electrons within the two V 3d orbitals and the π* orbitals of the three biphenyl ligands leads to a 40π Craig-Möbius aromatic system with three metalla-aromatic rings, as revealed by both experimental measurements and theoretical analyses. For comparison, if Cr is used instead of V, a similar Craig-Möbius aromatic system can not be generated. In this case, pentalithio spiro chromacycle 3 is obtained, and the Cr center uses its two 3d orbitals to form two independent metalla-aromatic rings. This work presents a type of aromatic systems that will contribute to both aromaticity theory and organometallic chemistry.

Organophotocatalytic dearomatization of indoles, pyrroles and benzo(thio)furans via a Giese-type transformation

Accessing fascinating organic and biological significant indolines via dearomatization of indoles represents one of the most efficient approaches. However, it has been difficult for the dearomatization of the electron deficient indoles. Here we report the studies leading to developing a photoredox mediated Giese-type transformation strategy for the dearomatization of the indoles. The reaction has been implemented for chemoselectively breaking indolyl C=C bonds embedded in the aromatic system. The synthetic power of this strategy has been demonstrated by using structurally diverse indoles bearing common electron-withdrawing groups including (thio)ester, amide, ketone, nitrile and even aromatics at either C2 or C3 positions and ubiquitous carboxylic acids as radical coupling partner with high trans-stereoselectivity (>20:1 dr). This manifold can also be applied to other aromatic heterocycles including pyrroles, benzofurans and benzothiophenes. Furthermore, enantioselective dearomatization of indoles has been achieved by a chiral camphorsultam auxiliary with high diastereoselectivity.

Aromatic Cope Rearrangements

Reviewed herein is the aromatic Cope rearrangement, a Cope rearrangement where one (or both) of the alkenes of the 1,5-diene are part of a greater aromatic system. While the Cope...

How aromatic system size affects the sensitivities of highly energetic molecules?

DFT calculations showed that with the increase of the aromatic system size, values of positive electrostatic potential above the central areas of energetic molecules decrease, leading to the decrease in the sensitivities towards detonation.

Fourier Transform Infrared Spectroscopy Evidence of the Nanoscale Structural Jump in Medium-Rank Tectonic Coal

Coal is a pressure-sensitive organic rock. The effect of tectonism on the structural evolution of medium-rank coal has been confirmed by the change in the crystal state of tectonic coal, but the organic molecular level response has not been reported. In this paper, three sets of medium-rank tectonic coals and symbiotic nontectonic coals were selected. The distributions of their functional groups and their molecular structure evolution were assessed using Fourier Transform Infrared Spectroscopy (FTIR), and their structural parameters were determined from the curve-fitting analysis. The nanoscale structural jump characteristics and mechanisms of medium-rank tectonic coal were revealed. Compared with symbiotic nontectonic coal, tectonism accelerated the exfoliation of side chains (groups) in the macromolecular structure, enlarged the aromatic system, and removed the unstable groups such as associative hydrogen bonds at first, which indicated that the molecular structure of tectonic coal was affected by nanoscale deformation, showing obvious advanced evolution characteristics. For the fat coal, the removal of side chains (groups) during the formation of tectonic coal makes the aromatic ring condensation obvious. For the coking coal, the formation of tectonic coal is dominated by cycloaliphatic dehydrogenation and aromatization, accompanied by the condensation of the aromatic rings. The tectonic coal formed from lean coal shows obvious aromatization characteristics. The molecular depolymerization and chemical tailoring caused by tectonism promotes the removal of hydrophobic side chains (groups) and activates some polar structure sites in coal. It is considered that the nanoscale structural jump of medium-rank tectonic coal is the result of the competition between the aromatic system and aliphatic structures.

The effects of chemical and thermal exfoliation on the physico-chemical and optical properties of carbon nitrides

Carbon-based nanomaterials, such as polymeric graphitic carbon nitrides, have garnered attention due to their metal-free structure, exceptional thermal and mechanical stability and unique extended aromatic system, imparting them with semiconductor...

Luminescent dysprosium single-molecule magnets made from designed chiral BINOL-derived bisphosphate ligands

The nature of the aromatic system and the number of chiral centers of the BINOL derived bisphosphate ligands influence both the chiroptical properties and single-molecule magnet behavior of a series of dysprosium-based chains.