Violation of Hund's rule in the lowest excited singlet-triplet pairs of dicyclohepta[cd,gh]pentalene and dicyclopenta[ef,kl]heptalene

Using the Pariser-Parr-Pople type MO method, the energy ordering of the lowest excited singlet-triplet pairs of the title molecules is examined by taking into account ample configuration interactions. In dicyclohepta[cd,gh]pentalene, it is shown that the lowest excited singlet state lies below the corresponding triplet state by about 6 kcal/mol. This violation of Hund's rule is ascribed entirely to the correlation effects brought about by spin polarization terms. Such a violation of Hund's rule is expected to occur in the lowest excited states of dicyclopenta[ef,kl]heptalene.     

Dicyclobuta[de,ij]naphthalene and dicyclopenta[cd,gh]pentalene: a theoretical study

The structures, energetics, and aromatic character of dicyclobuta[de,ij]naphthalene, 1, dicyclopenta[cd,gh]pentalene, 2, dihydrodicyclobuta[de,ij]naphthalene, 3, and dihydrocyclopenta[cd,gh]pentalene, 4, have been examined at the B3LYP/6-311++G//B3LYP/6-31G level of theory. All molecules are bowl-shaped, and the pentalene isomers, 2 and 4, are most stable. A comparison with other C(12)H(6) and C(12)H(8) isomers indicates that 2 is approximately 25 kcal/mol less stable than 1,5,9-tridehydro[12]annulene and 4 is approximately 100 kcal/mol higher in energy than acenaphthylene, both of which are synthetically accessible. The transition state structure for bowl-to-bowl inversion of 1 is planar (D(2)(h)()) and lies 30.9 kcal/mol higher in energy than the ground state; the transition state for inversion of 2 is C(2)(h)() and lies 46.6 kcal/mol higher in energy. Symmetry considerations, bond length alternations, and NICS values (a magnetic criterion) all indicate that the ground states of 1, 3, and 4 are very aromatic; however, HOMA values (a measure of bond delocalization) indicate that 3S and 4S are aromatic but that 1S is less so. NICS values for the ground state of 2 strongly indicate aromaticity; however, bond localization, symmetry, and HOMA values argue otherwise.     

Frontier orbital control in hydrazino bridged [14]annulenes

[10b.10c]Diazapyraceheptylenes 1b and 1c were obtained from olefinic precursors 6. Treatment of 7 under the same conditions does not allow a synthesis of the parent compound 1a which may be explained by frontier orbital considerations.     

Magnetic susceptibilities and resonance energies of annelated [14] - and [18] annulenes

Calculations of magnetic susceptibilities and topological resonance energies of annelated [14] - and [18] annulenes are reported. For several compounds the magnetic susceptibilities are also measured. In these cases a good agreement between calculated and experimental values of magnetic susceptibilities is obtained. All compounds studied are found to be diamagnetic. According to the magnetic exaltation criterion all compounds studied are predicted to be aromatic. This result is supported in the case of annelated annulenes by the TRE criterion. However, the parent structures, [14] annulene and [18] annulene, are found by the TRE to be non-aromatic. Finally, it is found that the aromatic stability does not parallel inert reactivity, i.e., some highly aromatic annulenoids are predicted by the low HOMO—LUMO separation to be rather reactive and some low aromatic structures are predicted by the high HOMO—LUMO separation to exhibit a considerable reactive inertness.     

Theoretical (DFT, GIAO-NMR, NICS) study of carbocations (M+H)+, dications (M2+) and dianions (M2-) from dihydro-dicyclopenta[ef,kl]heptalene (dihydro-azupyrene), dihydro-dicyclohepta[ed,gh]pentalene, and related bridged [14]annulenes

The annulenium ions of protonation, the two-electron oxidation dications, and the two-electron reduction dianions derived from dihydro- and dimethyldihydro derivatives (cis and trans) of dicyclopenta[ef,kl]heptalene (azupyrene) (1) and dicyclohepta[ed,gh]pentalene (2), which are the nonalternant isomers of pyrene, were studied by density functional theory (DFT) at the B3LYP/6-31G(d), 6-31+G(d,p), or 6-31++G(d,p) levels. Charge delocalization modes in the energetically most favored annulenium ions, as well as in the singlet and triplet dications and dianions, were assessed based on gauge-including atomic orbital (GIAO) Deltadelta](13)C values and via changes in natural population analysis (NPA) charges. Relative aromaticity/antiaromaticity in the annulenes were gauged via nucleus-independent chemical shift (NICS) and DeltaNICS. Annulenium ions of monoprotonation, the dications, and dianions derived from bismethano- and propanediylidene [14]annulenes were also studied by DFT for comparison with the cis-dihydro isomers derived from . Computed GIAO NMR data and the optimized geometries were compared with the experimental data when available, and the optimized geometries were compared with the X-ray data if known. A basis-set dependency study of the computed GIAO chemical shifts was also undertaken. The present DFT work represents the first detailed comparative theoretical study of charged annulenes derived from the dihydro derivatives of and .     

Preparation and characterization of 16-benzoylated tetraaza[14]annulenes

The condensation reaction between tetraaza[14]annulene ( 1 ) and a series of para-substituted benzoyl chlorides led to the 16-benzoylated corresponding products in 13–21% yields, but 1 was unreactive with alkyl acid chlorides and easily cleaved in macrocyclic framework. The mass spectra show the presence of molecular ion peaks which support the 16-benzoylated products. A strong ir band due to the C = N stretching mode of the macrocyclic moiety was observed at 1610 cm^?1 and shifted slightly toward higher energy upon benzoylation. An intense ir band which was associated with a C = 0 stretching mode was newly observed at 1640 cm¹. The very strong absorption band about 29000 cm^?1 was attributed to the π ? π* transition and gave a slight shift to higher frequency on benzoylation. All proton signals except for methyl protons exhibit downfield shifts due to the deshielding effect of the substituted benzene ring, but the methyl proton peaks show upfield shifts due to the shielding effect caused by the magnetic anisotropy of the substituted benzene ring. The ¹³C nmr result is also in accord with that of ¹H nmr.     

Synthesis of dibenzotetraaza[14]annulenes from 3-trimethylsiloxyacroleins

7,16-Dialkyl-5,14-dihydrodibenzo[b,i][1,4,8,11]tetraza[14]annulenes have been synthesized from o-phenylenediamine and 2-alkyl-3-trimethyl-siloxyacroleins. The probable mechanism is discussed. It is shown that metallo complexes of 7,16-dialkyldibenzotetraaza[14]annulenes have been prepared in high yield under template conditions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1400–1403, October, 1992.     

Electrophilic and oxidative chemistry of pyrene and its non-alternant isomers: theoretical (DFT, GIAO-NMR, NICS) study of protonation carbocations and oxidation dications from pyrene, azupyrene (dicyclopenta[ef,kl]heptalene) and dicyclohepta[ed,gh]pentalene

Mono- and diprotonated carbocations and the two-electron oxidation dications derived from parent pyrene and its nonalternant isomers "azupyrene"(dicyclopenta[ef,kl]heptalene)(DCPH) and dicyclohepta[ed,gh]pentalene (DCHP) were studied by DFT at the B3LYP/6-31G(d) level. The most likely site(s) for mono- and diprotonation were determined based on relative arenium ion energies and the structures of the energetically most favored carbocations were determined by geometry optimization. The NMR chemical shifts for the protonated mono- and dications and the oxidation dications were computed by GIAO-NMR at the B3LYP/6-31G(d)//B3LYP/6-31G(d) level and their charge delocalization paths were deduced based on magnitude of the computed [capital Delta][small delta](13)C values and the NPA-derived changes in charges. Relative aromaticity/antiaromaticity in various rings in the energetically favored mono- and dications was estimated via NICS and [capital Delta]NICS. Calculated NMR chemical shift data for and were compared with the available experimental NMR values. The available data on chemical and physical properties of DCPH and DCHP are extremely limited and biological activity data are non-existent. The present study provides the first glance into their carbocations and oxidation dications, while augmenting and reinforcing the previous stable ion data on the pyrenium cations.     

An ortho-fused tetrakisdehydro[14]annuleno[14]annulene consisting of two different types of bisdehydro[14]annulenes

Tetrakisdehydro[14]annuleno[14]annulene consisting of ‘acetylene-cumulene’ bisdehydro[14]annulene and Sondheimer's bishydro[14]annulene has been synthesized. It was found that a strong diatropicity was observed in the ‘acetylene-cumulene’ bisdehydro[14]annulene moiety, whereas diatropicity of another bisdehydro[14]annulene moiety shows marked decrease comparable with that of napthobisdehydro[14]annulene synthesized by Sondheimer.     

Generation and characterization of highly strained dibenzotetrakisdehydro[12]- and dibenzopentakisdehydro[14]annulenes

To generate dibenzotetrakisdehydro[12]- and dibenzopentakisdehydro[14]annulenes ([12]- and [14]DBAs) having a highly deformed triyne moiety, [4.3.2]propellatriene-anneleted dehydro[12]- and dehydro[14]annulenes were prepared as their precursors. UV irradiation of the precursors resulted in the photochemical [2 + 2] cycloreversion to generate the strained [12]- and [14]DBAs, respectively. The [12]DBA was not detected by 1H NMR spectroscopy, but it was intercepted as Diels-Alder adducts in solution, suggesting its intermediacy. Its spectroscopic characterization was successfully carried out by UV-vis spectroscopy in a 2-methyltetrahydrofuran (MTHF) glass matrix at 77 K and by FT-IR spectroscopy in an argon matrix at 20 K. On the other hand, the [14]DBA was stable enough for observation by 1H and 13C NMR spectra in solution, though it was not isolated because of the low efficiency of the cycloreversion. The [14]DBA was also characterized by interception as Diels-Alder adducts in solution and by UV-vis spectroscopy in a MTHF glass matrix at 77 K. The kinetic stabilities of the DBAs are compared with the related dehydrobenzoannulenes with respect to the topology of the pi-systems. In addition, the tropicity of the [14]DBA is discussed based on its experimental and theoretical 1H NMR chemical shifts.