Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

Nishinaga, Tohru; Ohmae, Takeshi; Iyoda, Masahiko

doi:10.3390/sym2010076

Cited by 100 publications

(80 citation statements)

References 95 publications

(124 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition to the standard sp 2 hybrid orbital of carbon atoms, which compose the hexagonal structure units, carbon atoms can also have distorted sp 2 hybrid orbitals, such as those that have been reported in square4849 or octagonal5051 structural units, such as in cyclobutadiene, biphenylene4849, and planar cyclooctatetraene5051525354555657. In short, 2D carbon crystals, in addition to graphene, could be fabricated from carbon atoms with the distorted sp 2 hybrid orbital.…”

Section: Discussionmentioning

confidence: 97%

A new type of two-dimensional carbon crystal prepared from 1,3,5-trihydroxybenzene

Tang

Huang

et al. 2017

Sci Rep

View full text Add to dashboard Cite

A new two-dimensional (2D) carbon crystal, different from graphene, has been prepared from 1,3,5-trihydroxybenzene, consisting of 4-carbon and 6-carbon rings in 1:1 ratio, named 4-6 carbophene by authors, in which all carbon atoms possess sp 2 hybrid orbitals with some distortion, forming an extensive conjugated π-bonding planar structure. The angles between the three σ-bonds of the carbon sp 2 orbitals are roughly 120°, 90°, and 150°. Each of the three non-adjacent sides of a 6C-ring is shared with a 4C-ring; and each of the two opposite sides of a 4C-ring is shared with a 6C-ring. Dodecagonal holes with a diameter of approximate 5.8 Å are regularly located throughout the 2D carbon crystal. Even though the bond energies in 4-6 carbophene are weaker than those in the graphene, the new planar crystal is quite stable in ambient conditions. The 4-6 carbophene can be synthetized from 1,3,5-trihydroxybenzene or other benzene derivatives through dehydration and polymerization reactions, and may possess several possible patterns that form a family of 2D carbon crystals. A possible side reaction involving 1,3,5-trihydroxybenzene is also discussed, which may produce a carbon-oxygen two dimensional crystal.Graphene 1,2 is an allotrope of elemental carbon in the form of an atomic-scale, two-dimensional, honey-comb lattice, in which all carbon atoms are in sp 2 electron configuration, resulting in an extensive conjugated π -system. Graphene is the basic structural element of several other carbon allotropes, including graphite 3,4 , carbon nanotubes 5 and fullerenes (C 60 ) 6 . Graphene is an excellent material possessing many outstanding physical and chemical properties, such as high electrical and thermal conductivity 7 , huge specific surface area 8 , good optical transparency 2 , and excellent mechanical strength 9,10 . Therefore, graphene is expected to have many applications in broad areas 11,12 .From material science and structural chemistry viewpoints, graphene is a two-dimensional (2D) crystal and a 2D carbon material 13 . Since the first 2D carbon crystal graphene was found in 2004 1,2 , several other 2D crystals and materials of carbon have emerged 14,15 . In recent years the 2D crystals and materials become a booming research field. A comprehensive review on this field can be found in a review article by Peng et al. 16 . Chemically, a sheet of graphene is a large aromatic molecule consisting of hexagonal planar structural units 17,18 that are similar to anthracene and phenanthrene. In graphene, all carbon atoms are in standard sp 2 electronic configuration so that the angles between the three σ -bonds of carbon sp 2 orbitals are 120°, 120°, and 120°, just as they are in the carbon atoms in benzene and other aromatic molecules 19,20 .Actually, the orbitals in carbon atoms can also be in a distorted sp 2 hybrid form, resulting in planar structural units other than hexagons [21][22][23][24] . This possibility raises an interesting question: "Are there other two-dimensional carbon crystals that are different from gra...

show abstract

Section: Discussionmentioning

confidence: 97%

A new type of two-dimensional carbon crystal prepared from 1,3,5-trihydroxybenzene

Tang

Huang

et al. 2017

Sci Rep

View full text Add to dashboard Cite

show abstract

“…Consequently, even when given the opportunity through the help of geometric distortions, an aromatic -electron system is not prone to distort, but in contrast adheres to a delocalized distribution which is not very different from that of the maximally aromatic equilibrium geometry. A similar tendency to adhere to a -electron delocalized arrangement in the lowest * excited triplet state of COT was earlier found by us through the ELF  properties [26], in line with the triplet state aromatic character of 4n -electron annulenes [90,[92][93][94][95][96][97].In its lowest * triplet state (T 1 ), COT at OLYP/6-311G(d,p) level has D 8h symmetry, a BV(ELF  ) of zero, and a RCBV(ELF  ) of 0.845 [26]. When the CC bonds of COT in the T 1 state were constrained at the optimal bond lengths of the S 0 state structure with D 4h symmetry (1.353 and 1.475 Å, respectively), a BV(ELF  ) of only 0.116 was calculated, whereas in the anti/nonaromatic S 0 state the BV(ELF  ) was as large as 0.637.…”

Section: The Elf  Bifurcation Values and CC Bond Lengthsmentioning

confidence: 54%

On the Importance of Clar Structures of Polybenzenoid Hydrocarbons as Revealed by the π-Contribution to the Electron Localization Function

et al. 2010

View full text Add to dashboard Cite

Abstract:The degree of -electron (de)localization and aromaticity of a series of polybenzenoid hydrocarbons (PBHs) has been analyzed through the π-contribution to the electron localization function (ELF π ), calculated at the B3LYP/6-311G(d,p) hybrid density functional theory level. The extent of -electron delocalization in the various hexagons of a PBH was determined through analysis of the bifurcation values of the ELF  basins (BV(ELF  )), the spans in the bifurcation values in each hexagon (ΔBV(ELF π )), and the ring-closure bifurcation values of the ELF π (RCBV(ELF π )). These computed results were compared to the qualitative description of local aromaticities of the different hexagons in terms of Clar structures with -sextets. Benzene, [18]annulene, and thirty two PBHs were analyzed at their equilibrium geometries, and benzene and triphenylene were also analyzed at bond length distorted structures. In general, the description of PBHs in terms of Clar valence structures is supported by the ELF  properties, although there are exceptions. For PBHs at their equilibrium geometries there is a clear sigmoidal relationship between the CC bond lengths and the amount of -electron (de)localization at these bonds, however, this relationship is lost for bond distorted geometries. In the latter cases, we specifically examined benzene in D 3h symmetric "1,3,5-cyclohexatriene" structures and triphenylene in eight different structures. From the distorted benzenes and triphenylenes it becomes clear OPEN ACCESSSymmetry 2010, 2 1654 that there is a distinct tendency for the -electron network to retain delocalization (aromaticity). The ELF  analysis thus reveals an antidistortive rather than a distortive behavior of the -electrons in these investigated compounds.

show abstract

“…1.45 Å and C=C double bonds of ca. 1.35 Å . The harmonic oscillator model of aromaticity (HOMA) value was estimated to be 0.644 for S 3 N 3 ‐ox .…”

Section: Resultsmentioning

confidence: 99%

Planar Antiaromatic Core‐Modified 24π Hexaphyrin(1.0.1.0.1.0) and 32π Octaphyrin(1.0.1.0.1.0.1.0) Bearing Alternate Hybrid Diheterole Units

Ajay

Shirisha

Ishida

et al. 2019

Chemistry A European J

View full text Add to dashboard Cite

The Lewis acid catalyzed self‐condensation of hybrid diheterole (furan‐pyrrole and thiophene‐pyrrole) precursors has afforded novel Hückel antiaromatic 24π hexaphyrin(1.0.1.0.1.0) and 32π octaphyrin(1.0.1.0.1.0.1.0) structures without β‐annulated bridges. Single‐crystal X‐ray diffraction analysis of the hybrid porphyrinoids (S3N3‐ox and O4N4‐ox) revealed a nearly planar conformation and the 1H NMR spectra suggest the presence of paratropic ring currents. These antiaromatic macrocycles show characteristic optical features and underwent reversible two‐electron reduction to Hückel aromatic 26π‐ and 34π‐electron species, respectively, as is evident from the results of spectroscopic and theoretical studies (nucleus‐independent chemical shift (NICS) and anisotropy of the current‐induced density (ACID) calculations). The incorporation of hybrid diheteroles alternately into expanded porphyrin skeletons provides a novel approach to the fine‐tuning of the electronic structures of planar antiaromatic macrocycles.

show abstract

Recent Studies on the Aromaticity and Antiaromaticity of Planar Cyclooctatetraene

Cited by 100 publications

References 95 publications

A new type of two-dimensional carbon crystal prepared from 1,3,5-trihydroxybenzene

A new type of two-dimensional carbon crystal prepared from 1,3,5-trihydroxybenzene

On the Importance of Clar Structures of Polybenzenoid Hydrocarbons as Revealed by the π-Contribution to the Electron Localization Function

Planar Antiaromatic Core‐Modified 24π Hexaphyrin(1.0.1.0.1.0) and 32π Octaphyrin(1.0.1.0.1.0.1.0) Bearing Alternate Hybrid Diheterole Units

Contact Info

Product

Resources

About