Unsaturated macrocyclic compounds. XCV. Thermolysis of [18]annulene

Stoeckel, Klaus; Garratt, Peter J.; Sondheimer, Franz; Zélicourt, Yves de Julien de; Oth, Jean F. M.

doi:10.1021/ja00779a093

Cited by 9 publications

(8 citation statements)

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“…[24,25] Although an [18]annulene complies with the spectral and structural criteria of aromaticity, as a consequence of the conformational flexibility it is a relatively reactive molecule, which decomposes at elevated temperatures with the tendency for addition/polymerization rather than electrophilic substitution reactions. [26,27] The last decade of the 20th century heralded a renaissance of annulene chemistry. [28] A number of synthetic discoveries in organic chemistry gave the ability to create new annulenes with a variety of uses or interest from the theoretical point of view, including the very first Mçbius annulenes [29,30] or porphyrinoids.…”

Section: Introductionmentioning

confidence: 99%

A Flexible Porphyrin–Annulene Hybrid: A Nonporphyrin Conformation formeso‐Tetraaryldivacataporphyrin

Pacholska‐Dudziak¹,

Szterenberg²,

Latos‐Grażyński³

2011

Chemistry A European J

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An annulene-porphyrin hybrid, the diaaza-deficient porphyrin 5,10,15,20-tetraaryl-21,23-divacataporphyrin, has been synthesized by an extrusion of tellurium atom(s) from 5,10,15,20-tetraaryl-21,23-ditelluraporphyrin under treatment with HCl. In addition, a monoaza-deficient 5,10,15,20-tetraaryl-21-tellura-23-vacataporphyrin was formed in the same reaction. The two new members of the vacataporphyrin family were characterized by X-ray crystallography, as well as UV/Vis and NMR spectroscopy. These aromatic molecules preserve the fundamental structural and spectroscopic features of the parent tetraarylporphyrin. The X-ray crystal structures of 21,23-divacataporphyrin and 21-tellura-23-vacataporphyrin show typical porphyrin patterns. The molecules are not strictly planar and show distortion of the annulene moieties. The N22⋅⋅⋅N24 distances (5.23 and 5.09 Å) are considerably longer than in regular porphyrins. For 21,23-divacataporphyrin, variable-temperature (1)H NMR spectroscopy data allowed the identification of divacataporphyrin stereoisomers differentiated by the geometry of the butadiene bridges. The forms remain in thermodynamic equilibrium.

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Section: Introductionmentioning

confidence: 99%

A Flexible Porphyrin–Annulene Hybrid: A Nonporphyrin Conformation formeso‐Tetraaryldivacataporphyrin

Pacholska‐Dudziak¹,

Szterenberg²,

Latos‐Grażyński³

2011

Chemistry A European J

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“…1,2 Originally, with its 18p electrons, its preparation served the understanding of larger aromatic compounds 3,4 that follow Hu ¨ckels (4n + 2)p rule and the distinction, up to which ring size aromaticity has an effect on bond length alternation and a stabilizing effect on the molecule. [5][6][7] Down to the present day, 1 has set off an avalanche of publications mostly theoretical in nature concerning e.g., the re-evaluation of its aromaticity, 8 or as a model compound for the ring-current in porphyrin 2 and related tetrapyrroles. 9 However, as for experimental research, 1 has withered away from the current literature, most likely due to its tendency to decompose, accompanied by unattractive overall yields of 0.4 to 0.6%, respectively.…”

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confidence: 99%

[18]Annulene put into a new perspective

et al. 2016

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“…(b) photochemical rearrangement of 2 carried out at -100°C in THF-d 8 (λ ) 350 nm) gives benzene and [12]annulene; 6,7 (c) catalytic hydrogenation of 2 indicates the presence of six double bonds in the molecule; the MS of the fully hydrogenated derivative(s) (molecular peak m/e ) 246) indicates a tetracyclic saturated C 18 -hydrocarbon. 7 We have therefore simulated the thermograms using the CALIT-3 program, considering two succesive first-order reactions (rate constants k 1 and k 2 ) according to the reaction given in Scheme 2.…”

Section: The Thermal Rearrangement Of [18]annulenementioning

confidence: 99%

“…7 We have therefore simulated the thermograms using the CALIT-3 program, considering two succesive first-order reactions (rate constants k 1 and k 2 ) according to the reaction given in Scheme 2.…”

Section: The Thermal Rearrangement Of [18]annulenementioning

confidence: 99%

“…In an independent experiment, we have isolated the intermediate(s) and could show that it corresponds to one or more tetracyclic structures 2 of molecular formula C 18 H 18 . 7 The 1 H-NMR spectrum of the isolated intermediate(s) 2 as well as the spectrum of the hydrogenated product(s) are represented in Figure 4. 1,8 The intermediate compound(s) 2 must have one of the three possible structures 2a, 2b, or 2c (c ) cis ring fusion; t ) trans).…”

Section: The Thermal Rearrangement Of [18]annulenementioning

confidence: 99%

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Elucidation, by Scanning Microcalorimetry, of the Detailed Mechanism of the Thermal Rearrangement of [18]Annulene into Benzene and 1,2-Benzo-1,3,7-cyclooctatriene. Determination and Interpretation of the Thermochemical and Kinetic Parameters of the Three Consecutive Reactions Implicated

Oth

Gilles

2000

J. Phys. Chem. A

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The thermograms Q 4 r (T) recorded for the thermal rearrangement of [18]annulene 1 have been reinvestigated using an iterative method (CALIT-3 program) based on the numerical integration of the kinetic equations established for the following reaction mechanism: [18]annulene 1 98 k 1 tetracyclic intermediates 2 98 k 2 transbicyclo[6.4.0]dodeca-2,4,6,9,11-pentaene 3 + benzene 5; 3 98 k 3 1,2-benzo-1,3, 7-cyclooctatriene 4. Independent 13 C-NMR experiments indicate that three chiral tetracyclic intermediates 2a, 2b, and 2c are implicated in the reaction. They are considered to play the same role in the mechanism and are therefore considered as a single compound 2 in the kinetic equations. A programmed differential microcalorimeter with linearly increasing temperature was used for producing the thermograms. The reaction enthalpies ∆ r , i H of each individual reaction (i ) 1, 2, or 3) as well as the Arrhenius parameters E a,i , log A i and the activation thermodynamic quantities ∆H q i , ∆S q i , and ∆G q i (at 298.2 K) have been established by the iterative numerical simulation of the thermograms. These results are discussed. The enthalpy of formation of [18]annulene 1, as well as the stabilization and π-bond delocalization energies of this molecule have been deduced: ∆H°f (1, g, 298.2 K) ) 123.4 ( 3.7 kcal mol -1 ; ∆H stab (1) ) -37.6 ( 4.5 kcal mol -1 ; ∆H deloc (π-bonds in 1) = -120.5 kcal mol -1 . The stabilization enthalpy ∆H stab (1) has been used for discussing the activation enthalpy of the conformational mobility in 1 previously reported. The pathway multiplicities deduced from the detailed mechanisms for each individual reaction are discussed in view of the interpretation of the large activation entropies found. Of special interest is the discussion of the mechanism of the two suprafacial 1,5 hydrogen shifts implied in the reaction 3 98 k 3 4 and of the high activation entropy observed. In independent measurements, the rate of disappearence of the [18]annulene 1 has been followed by UV spectroscopy in order to obtain the kinetic parameters for the first reaction. The results of these independent measurements are in good agreement with those obtained by the analysis of the thermograms. The reported investigation points to the fact that the thermograms recorded with our calorimetric method constitute very precise data and that their correct analysis allows the elucidation of complex reaction mechanisms.

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Unsaturated macrocyclic compounds. XCV. Thermolysis of [18]annulene

Cited by 9 publications

References 1 publication

A Flexible Porphyrin–Annulene Hybrid: A Nonporphyrin Conformation formeso‐Tetraaryldivacataporphyrin

A Flexible Porphyrin–Annulene Hybrid: A Nonporphyrin Conformation formeso‐Tetraaryldivacataporphyrin

[18]Annulene put into a new perspective

Elucidation, by Scanning Microcalorimetry, of the Detailed Mechanism of the Thermal Rearrangement of [18]Annulene into Benzene and 1,2-Benzo-1,3,7-cyclooctatriene. Determination and Interpretation of the Thermochemical and Kinetic Parameters of the Three Consecutive Reactions Implicated

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