Tetrakisdehydro[18]annuleno[20]annulene

Tetrakisdehydro[18]annuleno[20]annulene has been synthesized. The ¹H NMR spectra clearly indicate the induction of dia- and paramagnetic ring currents in 18- and 20-rings, respectively. A marked suppression of the diatropicity in the 18π moiety was observed being in the same trend in other tetrakisdehydro[4n]annuleno[4n′+2]annulenes. The ¹H NMR spectroscopic behavior of the annulenoannulenes is consistent with theoretical conclusion.     

Tetrakisdehydro[14]annuleno[16]annulene

Tetrakisdehydro[14]annuleno[16]annulene consisting of an aromatic bisdehydro[14]-annulene and an antiaromatic trisdehydro[16]annulene has been synthesized. The ¹H NMR parameters clearly indicate the strong paratropicity and diatropicity of the 16-membered and 14-membered rings, respectively.     

Tetrakisdehydro[16]annuleno[18]annulene

Tetrakisdehydro[16]annuleno consisting of trisdehydro[16]annulene and bisdehydro[18] annulene has been synthesized. Induction of para- and diamagnetic ring currents in 16- and 18-membered rings, respectively, was clearly recognized by the ¹H NMR spectroscopy. A marked suppresion of the diatropicity in the 18π moiety was observed in the same trend as observed in tetrakisdehydro[14]annuleno[16]annulene.     

A naphtho-tri-t-butyltrisdehydro[16]annulene

Synthesis of a naphtho-tri-t-butyltrisdehydro[16]annulene has been described. Suppression of paratropicity of the 16-membered ring was observed. Comparison of ¹H NMR spectrum of the [16]annulene with that of naphtho-tri-t-butylbisdehydro[14]annulene suggests that the trans double bond adjacent to naphthalene in the [16]annulene is twisted out of the mean molecular plane.     

Trisdehydro[14]annuleno[16]annulene

Trisdehydro[14]annuleno[16]annulene consisting of an aromatic bisdehydro[14]annulene and an antiaromatic bisdehydro[16]annulene has been synthesized. The strong paratropicity was observed in the [16]annulene moiety being comparable with that of extremely unstable parent bisdehydro[16]annulene.     

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.     

The structures of the two isomers of monodehydro[14]annulene

Variable temperature ¹H nmr spectrometry has shown that the “unstable” isomer of monodehydro[14]annulene possesses the symmetrical di-$\text{trans}$ configuration $\text{1}$ or $\text{2}$, and the “stable” isomer (the precursor of [14]annulene) possesses the tri-$\text{trans}$ configuration $\text{4}$.     

Perimeter-Type Structures in Charged [4n + 2] Annuleno [4n + 2] annulenes. The Importance of the Frontier-Orbitals

The tetra(tert-butyl)[14]annuleno[14]annulene 1 is transformed, via alkali metal reduction, into its radical monoanion, dianion, radical trianion, and tetraanion. The paramagnetic species are characterized by ESR and ENDOR spectroscopy and the diamagnetic species by ¹H- and ¹³C-NMR spectroscopy. Well-resolved ESR and NMR spectra can only be obtained, if the reduction is carefully monitored. For the interpretation of the data, the ions derived from the structurally related [14]- and [22]annulenes 3 and 5 as well from the tetra(tert-butyl)[14]annuleno[18]annulene 2 serve as suitable model compounds. While the behavior of the neutral annulenoannulene 1 is governed by that of the [14]annulene-subunit, the corresponding ionic systems can best be described as macrocyclic perimeters. This outcome can be rationalized by the nodal properties of the frontier MO's.     

Syntheses of an isoannelated annulene,a bisdehydro[14]annuleno[c]furan and bisdehydro[14]annulene derivatives

A bisdehydro[14]annuleno[c]furan, an isoannelated diatropic annulene, has been synthesized. Cyclic glycol, a precursor of the annuleno[c]furan, could be converted into bisdehydro[14]annulene derivatives under mild acidic conditions.     

Preparation and characterization of tetraaza[14]annulene and its nickel(ii) and copper(II) complexes with crown ether functionalities

Three new organic hosts are described that contain a tetraaza[14]annulene core to which two crown ether voids are attached. These hosts include a free base tetraaza[14]annulene and/or its complexes with benzo-15-crown-5 rings. The crown tetraaza[14]annulene is synthesized from tetraaza[14]annulene and 4′-chloroformylbenzo-15-crown-5. Its nickel(II) and copper(II) complexes are prepared in a similar manner as above. In solution the compounds do not tend to form aggregates. However, aggregation is affected by the presence of alkali-metal salts, which coordinate to the crowns. Li⁺ and Na⁺ cations with diameters that match the diameters of the crown ether rings form 1:2 host-guest complexes. Complexes with 2:2 host-guest stoichiometry are formed when the diameters of K⁺ and Cs⁺ cations exceed that of the crown ether rings. Nevertheless, it is weak for the present macrocycle and its complexes to be inclined to form dimers owing to the steric hindrance of the substituent groups and owing to restraining the rotation of the carbonyl bond connecting the crown ether group.     

1,6:9,14-bismethano[16]annulene - a new bridged [4n]annulene

The molecular structure and dynamic behaviour of the bridged [4n] annulene 1,6:9,14-bismethano-[16]annulene is unravelled by NMR and X-ray investigations, combined with force field calculations.     

Unsaturated macrocyclic compounds-CIX : Synthesis of a tetradehydrotetraaza[32]annulene

The conjugated aldehydes 6,9, and 12, containing terminal acetylenes, were prepared and converted to the corresponding azines 13, 14, and 15, respectively. Oxidative coupling of 14 gave the corresponding cyclic “dimer” 16, a tetradehydrotetraaza[32]annulene. Although 16 is a 4n π-electron system, the ¹H-NMR spectrum showed it to be an atropic molecule.     

The Stabilization Energy of [18] Annulene. A thermochemical determination

The thermal rearrangement of [18]annulene in solution gives benzene and 1,2-benzo-1,3,7-cyclooctatriene. This reaction has been investigated using a differential scanning calorimeter and the associated enthalpy change has been measured. The enthalpy of the reaction (in the gase phase at 298°K) is From this value and the enthalpies of formation of the reaction products, the enthalpy of formation of [18]annulene is obtained: The stabilization energy of [18]annulene, defined as the difference between the enthalpy of formation of the hypothetical Kékulé [18]annulene (with single and double bonds of normal lengths) and the heat of formation of the real molecule is then a value close to the corresponding quantity found for benzene. The very large stabilization energy of [18]annulen (100 ± 6 kcal mol^?1) previously reported in the literature, based on measurements of the heat of combustion, is not correct since the annulene is certainly oxidized in the bomb prior to combustion. The isodynamic conformational mobility of [18]annulene is not incompatible with a stabilization energy of 37 kcal mol^?1; the activation enthalpy observed for this process (ΔH^≠ = 16.1 kcal mol^?1) indicates that the stabilization is not completely destroyed in the transition state. The mechanism of the thermolysis of [18]annulen, investigated by kinetic measurements and by analysis of the shape of the thermograms, is discussed.     

Electronic Structure,Aromaticity and Optical Properties of Dehydro[10]annulene

Dehydro[10]annulene had been prepared experimentally recently, which is considered to be a highly rigid structure with planar configuration. In this paper, the electronic structure and bonding character of dehydro[10]annulene had been studied by means of molecular orbital (MO), density of states (DOS), bond order (BO) and interaction region indicator (IRI) analyses. The delocalization characters of out-of-plane and in-plane π-electrons (π^out- and πⁱⁿ-electrons) of the bond regions were studied by using localized orbital locator (LOL). The anisotropy of the induced current density (AICD), iso-chemical shielding surface (ICSS) and anisotropy of the gauge-including magnetically induced current (GIMIC) were used to investigate the molecular response to external magnetic field, including the induced ring current and the magnetic shielding characteristic. The results showed that the electron delocalization of dehydro[10]annulene is mainly contributed by π^out system. The apparent clockwise current in the π^out system proved that dehydro[10]annulene is π^out aromatic. Finally, the photophysical properties and (hyper)polarizability of dehydro[10]annulene were studied by TD-DFT calculation. The results showed that dehydro[10]annulene has strong local excitation characters. Its (hyper)polarizability decreases with the increase of frequency and has the characteristics of nonlinear anisotropy.     

ESR.-Spektren des Radikal-Anions des syn-1, 6; 8, 13-Bis-oxido-[14]annulens

The ESR.-spectra of the radical anion of syn-1, 6; 8, 13-bis-oxido-[14]annulene have been recorded. The hyperfine structure of the electrolytically generated anion (solvent: N, N-dimethylformamide; gegenion: Et₄N^⊕) is that of an unassociated species; on the other hand, evidence of strong ion-pairing can be derived from the spectra of chemically prepared anions (solvent: 1,2-dimethoxyethane; gegenion: K⊕ or Na⊕). The distribution of the n-spin population confirms the conclusion previously drawn for the radical anion of 1,6-oxido-[70]annulene that the overall effect of the oxygen bridging is electron repelling.     

Die Bildungsenthalpie 1,6-überbrückter [10] Annulene

The enthalpies of formation of 1.6-methano-[10] annulene (IV) (ΔHf₂₉₈ (IV, g) = 75.2 ± 0.6 kcal mol^?1), 1.6-imino-[10] annulene (V) (ΔHf₂₉₈(V, g) = 87.8 ± 0.7 kcal mol^?1) and of 1.6-oxido-[10] annulene (VI) (ΔHf₂₉₈(VI, g) = 47.8 ± 1.2 kcal mol^?1) have been determined by combustion calorimetry. The difficulties connected with an attempt to derive meaningfull «resonance energies» are discussed.     

Synthese eines 2,5,7,10-substituierten 1,6-Methano[10]annulens,seine Methylierung, Ätherspaltung und Deprotonierung

Synthesis of a 2,5,7,10-Substituted 1,6-Methanol[10]annulene, its Methylation, Ether Cleavage; and Deprotonation The synthesis of 2,7 -di(tert -butoxy)-1,6-methanol[10]annulene derivatives 2 and 3 are described. Methylation of 3 gave 4 , and 4 was transformed, on treatment with p-toluene sulfonic acid, to the salt 5 . Basic reagents deprotonated 5 ; the resulting solution was analyzed by ¹H-NMR spectroscopy.     

2,5-Chinonmethide des 1,6-Methano[10]annulens mit S,N- und N,N-Acylketenacetal Struktur

2,5-Quinonemethides of 1,6-Methano[10]annulene with the Structures of S,N- and N,N-Acylketene Acetals Investigation on the chemical reactivities of 2-(tert -butoxy)-1,6-methano[10]annulene and the syntheses of the compounds 2, 4, 6–8, 11, 13–22 are described; the results of ¹H- and ¹³C-NMR-spectroscopic measurements are reported.     

Radikalionen von überbrückten [14] Annulenen. Untersuchungen zum Frontorbitaleinfluss auf Reaktivität und Bindungszustand

Radical Ions of Bridged [14] Annulenes. Investigations on the Influence of Frontier Orbitals on Reactivity and Bonding The radical anions and the radical cations derived from trans-15, 16-dimethyl-1, 4:8,11-ethandiyliden[14]annulene ( 6 ), trans-15-methyl-1,4:8,11-ethandiyliden[14]annulene ( 7 ) and cis-15, 16-propano-1,4:8,11-ethandiyliden[14]annulene ( 8 ) are described. The hyperfine data of the radical anions 6, 7 and 8 resemble those of the structurally related radical anions of trans-10b, 10c-dimethyldihydropyrene ( 4 ) and trans-10b, 10c-dihydropyrene ( 5 ). This finding leads to the conclusion, that the change in the relative arragement of the saturated bridge within the fourteen-membered π-perimeter by passing from 4 (5) to 6 ( 7, 8 ) does not in fluence the energetic sequence of the lowest unoccupied molecular orbitals. The behavior of 6 and 7 towards oxidation parallels the photochemical reactivity of 4 . The hyperfine coupling constants of the radical cations derived from 6 and 7 indicate that the removal of an electron is accompanied by an isomerization of the molecular framework. The investigation of the electron transfer process gby cyclic voltammetry supports these findings. The radical cations prefer the cyclophane-like structures 6a and 7a , in which the central σ-bond (C(15)–C(16) bond) is broken.     

Diepoxy[18]annulene(10.0) : (Z,E,Z,E,Z)‐Diepoxy[18]annulen(10.0) – ein hochdynamisches Annulen

Diepoxy[18]annulenes(10.0): ( Z , E , Z , E , Z )‐Diepoxy[18]annulene(10.0) – a Highly Dynamic Annulene The McMurry reaction of (all‐E)‐5,5′‐([2,2′‐bifuran]‐5,5′‐diyl)bis[penta‐2,4‐dienal] ( 13 ) only occurs intramolecularly to give a mixture of the diepoxy[18]annulenes(10.0) 6 and 7 . Tetraepoxy[36]annulene(10.0.10.0) resulting from an intermolecular McMurry reaction is not formed. According to spectroscopic data, 6 is (Z,E,Z,E,Z)‐ and 7 (Z,E,E,Z,E)‐configured. The ¹H‐NMR data confirm that in 6 the (E)‐ethene‐1,2‐diyl bonds (C(11)=C(12) and C(15)=C(16)) rotate around the adjacent σ‐bonds. Beginning at −70°, this rotation freezes, and 6 is becoming a diatropic aromatic ring system. Beside [18]annulene itself, (Z,E,Z,E,Z)‐diepoxy[18]annulene(10.0) 6 is the only hitherto known [18]annulene derivative with dynamic properties.