Étude des dispersions diamagnétiques

Pacault, A.

doi:10.1051/jcp/1952490585

Cited by 11 publications

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“…In the series 5, 6, 7, 13 and 23 all compounds should be about equally aromatic by both ÁE(ND) and NICS criteria. A small but hardly significant increase could be expected in benzaldehyde (13). Five-membered rings 14-17 and 19-22 should be considerably less aromatic than benzene according to the ÁE(ND) diagnostic, but almost as aromatic as benzene if the NICS criterion is applied.…”

Section: Resultsmentioning

confidence: 94%

“…(3) The magnetic behavior of aromatic compounds has some unusual features, which are used as magnetic probes of aromaticity. For example, the enhancement of magnetic susceptibility (Ã) relative to the combined atom and bond additivity scheme of Pacault et al 13,14 was considered as a signature or fingerprint of aromaticity. Further, according to Benassi et al 15 the magnetic susceptibility component perpendicular to the molecular plane is an even more reliable index than those based on magnetic anisotropy or NMR data.…”

Section: Introductionmentioning

confidence: 99%

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Non‐additivity of the static correlation energy of π‐electrons in planar molecules as a manifestation of anti/aromaticity

Barić

Maksić

2003

J of Physical Organic Chem

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The non-dynamic or static correlation energy of -electrons, E(ND) , was studied in a number of cyclic organic molecules, including various heteroatomic systems, employing CASSCF formalism. It is shown that E(ND) is highly additive in linear polyenes. However, interesting non-additivities are found in anti/aromatic molecules. They are seemingly counterintuitive since E(ND) is smaller in aromatic compounds than in the corresponding open-chain polyenes. The opposite takes place in antiaromatic systems. However, they are easily understood if it is taken into account that the HF HOMO-LUMO gaps are higher in aromatic and lower in antiaromatic molecules compared with reference zig-zag polyenes. The results of the present analysis confirm that anti/aromaticity is an excess or depletion feature, meaning that deviations of E(ND) from additivity are a direct consequence and clear manifestation of anti/ aromaticity. It is argued that anti/aromaticity is necessarily a multifaceted phenomenon, since each molecular property probes different portions of the electron density distribution and/or a ladder of the molecular orbital energy levels, thus leading to distinct scales of anti/aromaticity. Each of these scales is useful in its own right. However, the most important scale is based on homodesmotic reactions, since they are directly related to thermodynamic in/ stability and consequently to the omnipresent chemical reactivity.

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Section: Resultsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Non‐additivity of the static correlation energy of π‐electrons in planar molecules as a manifestation of anti/aromaticity

Barić

Maksić

2003

J of Physical Organic Chem

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“…The diamagnetic anisotropy AK is defined by the following equation, where x, is the mean molar susceptibility and Ki is the isotropic part of molar susceptibility. The latter can be estimated by empirical rules (23,24). Followiilg our previous paper (ti), the isotropic part will be estimated by where Nc, N,, No are the numbers of aromatic carbon atoms, hydrogen atoms, and quinone oxygen atoms in a molecule.…”

Section: Discussionmentioning

confidence: 99%

Magnetic Properties of Mesonaphthodianthrene

Matsunaga¹

1960

Can. J. Chem.

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Electron spin resonance absorption was detected in lnesonaphthodianthrene and mesonaphthodianthrone. The spectra of both of these co~npounds consist of, a t least, seven lines with a separation of 4.4 oersteds and the central line has a g-value of 2.0024f 0.0002. The growthof the central line by admission of air was observed in the case of the hydrocarbon. Some suggestions are presented as to the nature of the unpaired electrons in these compounds. The magnitude of the molar diamagnetic susceptibility of mesonaphthodianthrene, after correction for the paramagnetic contribution from the unpaired electrons, is discussed in relation to the molecular structure. IXTRODUCTIONThe appearance of unpaired electro~ls has been reported in crystals of solne highly conjugated molecules, namely metal-free phthalocyanine (1, 2), violanthrone (3, 4), violanthrene (3, 4), and binaphthoquinones (5). Here we wish to present the results of a study of mesonaphthodianthrene (I) and ~neso~laphthodianthrone (11) by the electron spin resonance method. The hydrocarbons studied are co~npounds which have anomalously small values of diamagnetic susceptibility (6). This anomaly was found to be characteristic of perylene (111) and its analogues. In the sense oi the valence-bond theory the central single bonds in perylene, violanthrone (IV), and mesonaphthodianthrene can be doubled only in the excited states. EXPERIMENTAL J/Iesonaphthodianthrone was prepared by photodehydrogenation of bianthraquinone dissolved in pyridine (7). The hydrocarbon was obtained by the zinc-dust fusion of the quinone (8). The latter was found t o be reactive towards oxygen, therefore our sample was stored in an evacuated tube after repeated sublimation in high vacuum.The electron spin resonance mas examined a t a frequency of 9 ki\/Ic/s a t room temperature, and a t 7 7 O I<. RESULTSUnlilte the spectra of the other paramagnetic polycyclic aronlatic compounds, the spectra of mesonaphthodianthrene and its quillone show solne structure and this can be modified by admissio~l of air. The spectra of these two compounds consist of a t least seven lines with a separation of 4.4 oersteds and spread over 50 oersteds as shown in Fig. 1 Can.

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“…The London quadrupole susceptibility contributes for a major part to the large diamagnetic anisotropy of single crystals of aromatic polycyclic hydrocarbons. This London susceptibility is closely related to the diamagnetic exaltation, introduced in magnetochemistry by Pacault in 1946 [3] and which can be considered as a magnetic analog of the resonance energy. The diamagnetic exaltation has been proved to be a good criterion of aromaticity [4, 51.…”

Section: Introductionmentioning

confidence: 91%

“Ring currents” static hypersusceptibilities

Gayoso

Maouche

Ouamerali

et al. 1980

Int J of Quantum Chemistry

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The Huckel-London theory has been applied to the calculation of the "ring currents" octopole hypersusceptibilities of a series of conjugated compounds. Our calculations have been performed using fourth-order Rayleigh-Schrodinger perturbation technique. This is believed to be the first calculation of this kind. It is found that the values of "ring currents" hypersusceptibilities of fulvene and aiulene are larger, in absolute magnitude, than the values corresponding, respectively, to beniene and naphthalene. It is found that, in most cases, the "ring currents" hypersusceptibilities arc diamagnetic (negative values) for aromatic molecules and paramagnetic (positive values) for pseudoaromatic or antiaromatic compounds.

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Étude des dispersions diamagnétiques

Cited by 11 publications

References 0 publications

Non‐additivity of the static correlation energy of π‐electrons in planar molecules as a manifestation of anti/aromaticity

Non‐additivity of the static correlation energy of π‐electrons in planar molecules as a manifestation of anti/aromaticity

Magnetic Properties of Mesonaphthodianthrene

“Ring currents” static hypersusceptibilities

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