Cyclooctannelated biphenylenes. Diagnosis of an anomalous bond length by analysis of ring current geometric factors

Wilcox, Charles F.; Farley, Erik N.

doi:10.1021/jo00203a013

Cited by 24 publications

(16 citation statements)

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“…When the 4–6 films are removed from the glass sheet using N,N-dimethyl formamide, transparent carbon films are obtained. The SEM (scanning electron microscopy) images35 of the films are shown in Fig. 3(c) and (d).…”

Section: Resultsmentioning

confidence: 99%

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

Tang

Huang

et al. 2017

Sci Rep

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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...

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Section: Resultsmentioning

confidence: 99%

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

Tang

Huang

et al. 2017

Sci Rep

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“…As Pople and Untch [57] further observed, even when only monocyclic conjugated systems are considered, for the larger annulenes '... the paramagnetic currents will be partly quenched by alternation of bond-lengths and molecular non-planarity'. It should also be noted that those versions of the so-called 'tight-binding' [60] HLPM calculations that do not iterate resonance integrals with respect to bond orders, nor Coulomb integrals with respect to charges on the carbon atoms, [48,[61][62][63][64][65] '... can yield unsafe predictions when the geometrical distortion is important' [14] Indeed, from much earlier investigations, [47,48,[61][62][63][64][65] one of us (RBM) has vigorously emphasised [47] that such self-consistency is virtually vital in order to be sure of even qualitatively reliable ring-currents in the case of very paramagnetic conjugated species. As noted by Wilcox and Farley many years ago, [48] one of the present authors (RBM) even concluded [47] that this sensitivity to the sophistication of the computational method employed -especially for paramagnetic species -is a major drawback to the potential utility of adopting calculated London susceptibility ratios (equation (1)) as a criterion for defining 'aromaticity'.…”

Section: Discussionmentioning

confidence: 99%

“…That is why, in the current work, and earlier but recent ones, [27][28][29][30][31][32][33] the above reservation about non-iterative calculations expressed in Refs. [47,[61][62][63][64][65] have been temporarily set aside in order to test how well the predictions of the ab initio methods compare with even the most basic, non-iterative pseudograph-theoretical version of the Hückel-London-PopleMcWeeny approach; [1][2][3][4][5][6] in this formalism, the calculated quantities (ring currents and bond currents) are effectively regarded -despite the cautions and caveats considered by one of us (RBM) in Ref. [66] -as effectively mathematical, pseudo graph-theoretical indices, rather than as quantummechanically calculated physical quantities per se.…”

Section: Quantitative Comparisons With Ab Initio Calculationsmentioning

confidence: 99%

Ring-Current Properties of Bispentalenes and Related Structures — Comparison of Ab Initio and Hückel-London-Pople-McWeeny (HLPM) ‘Topological’ Calculations

Dickens¹,

Mallion²

2017

Croat. Chem. Acta

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Two different groups (Cao et al. (2015) and ) have recently reported (a) experimental Nuclear Magnetic Resonance data and ab initio Nucleus Independent Chemical Shift (NICS) calculations, and (b) GIMIC (Gauge Including Magnetically Induced Currents) ab initio computations, on the magnetic properties of some derivatives of [4n+2]-π-electron conjugated systems called 'bispentalenes'. These are formed by annellating two pentalene groups with a benzene or a naphthalene moiety. The same structures are here subjected to calculations based on the simple, pseudo graph-theoretical, Hückel-London-Pople-McWeeny (HLPM) 'topological' ring-current approach. In addition, HLPM calculations are presented on some structures with [4n]-perimeters that were also studied by Cao et al., as well as some other related, specially 'designed', [4n]-and [4n+2]-perimeter structures of our own choosing. The aim is to see whether there is qualitative, or even semi-quantitative, agreement between a (presumably) numerically accurate but necessarily complex ab initio calculation and a conceptually simple, quasi graph-theoretical one -the HLPM approach -whose predictions depend only on the carbon-carbon connectivity of the structure being investigated, and on the (geometrical) areas of its individual constituent rings. The HLPM calculations agree with the more-sophisticated studies that all the structures examined, whether they be [4n]-or [4n+2]-perimeter systems, bear paramagnetic π-electron currents around their perimeters. Furthermore, all the many pentalene moieties in these conjugated systems appear to undergo incorporation into these bispentalene structures with -to greater or lesser extents -their characteristic perimeter circulations in the paramagnetic sense surviving intact. Quantitative regression comparisons between GIMIC ab initio integrated bond-current susceptibilities and HLPM bond-current intensities in a small sample of bonds in the structures studied by Sundholm et al. are found to have a correlation coefficient of 0.94 -not as high as that obtained (0.98) when similar data for a larger sample of bonds in several alternant, condensed, benzenoid were previously compared. It is again emphasised that Pople and Untch's rule about [4n+2]-annulenes being diamagnetic and [4n]-ones being paramagnetic -like the famous Hückel Rule itself -rigorously applies only to monocycles.

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“…In their pioneering work, Wilcox and co-workers correlated aromaticity and ring currents to geometric parameters. [48][49][50] From a structural viewpoint, the main characteristic of aromatic systems is their tendency to exhibit bondlength equalization. [51] Some earlier work on rather limited sets of PAHs led to the conclusion that the latter three (physicochemical) definitions of aromaticity correlate well with each other.…”

Section: Introductionmentioning

confidence: 99%

Aromaticity of Giant Polycyclic Aromatic Hydrocarbons with Hollow Sites: Super Ring Currents in Super‐Rings

Hajgató

Deleuze

Ohno

2006

Chemistry A European J

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We present a systematic theoretical study based on semi-empirical, Hartree-Fock (HF), and density functional theory (DFT) models of a series of polycyclic aromatic hydrocarbons (PAHs) that exhibit hollow sites. In this study we focus particularly on the magnetic criteria of aromaticity, namely (1)H NMR and nucleus-independent chemical shifts (NICS), and on their relationships with other electronic properties. The computed shifts and NICS indices indicate that an external magnetic field induces exceptionally strong ring currents in even-layered PAH doughnuts, in particular in the layer directly adjacent to the central hole of double-layered compounds. These exceptionally strong ring currents also correlate with particularly small HOMO-LUMO gaps and electronic excitation energies and to abnormally high polarizabilities, indicating in turn that these compounds have a more pronounced metallic character. Comparison is made with further depictions of aromaticity in these systems and in [18]-[66]annulene rings by employing topological, structural, and energetic criteria.

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Cyclooctannelated biphenylenes. Diagnosis of an anomalous bond length by analysis of ring current geometric factors

Abstract: The syntheses and properties of the benzocyclobutene-and naphtho [ 5 ] cyclobutene-fused dicyclooctabiphenylenes 8 and 9 are described. These ir systems show paratropic

Cited by 24 publications

References 2 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

Ring-Current Properties of Bispentalenes and Related Structures — Comparison of Ab Initio and Hückel-London-Pople-McWeeny (HLPM) ‘Topological’ Calculations

Aromaticity of Giant Polycyclic Aromatic Hydrocarbons with Hollow Sites: Super Ring Currents in Super‐Rings

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