1999 R.U. Lemieux Award Lecture Adventures with azo-, azoxy-, and hydrazoarenes: from the Wallach to the benzidine rearrangement. Molecular electronics
Notice bibliographique
Résumé
The author's studies with aromatic azo-, azoxy-, and hydrazo-dye molecules, comprising kinetic and equilibrium investigations, as well as synthesis of novel molecules having photogenic properties, are described under the following highlights: A. Wallach rearrangement and cognate studies with azoxyarenes (1) Elucidation of the mechanism of the Wallach rearrangement of azoxybenzene through the kinetic observation of a two-proton process which, together with a pKa study, was interpreted on the basis of formation of a deoxygenated, dicationic, symmetrical species as a key, short-lived reaction intermediate. (2) The proposal of a general acid-catalyzed pathway in concentrated sulfuric acid (catalysis by H2SO4 and H3SO+4. (3) Elucidation of the consecutive sulfonations of reaction products of azoxybenzene in the 100% H2SO4 region, and the diprotonation equilibria for p-hydroxyazobenzene, thus shedding light on past reaction pathway and product studies. (4) The observation of a novel reaction pathway for 2,4,6,2',4',6'-hexamethy lazoxybenzene. (5) The observation of a dichotomy of reaction pathways for α- and β-2-phenylazoxynaphthalenes: reaction via the dicationic intermediate and via quinoid intermediate species; comprising two isomeric compounds reacting by different pathways to give the same product. (6) Identification and structure proof of α- and β-isomers observed for the first time in the peracid oxidation of phenylazopyridine. (7) Observation of a rate constant ratio of 22 000 in the rearrangement of these α- and β-isomers, and the proposal of differential barriers for transition states leading to a tricationic intermediate. B. Benzidine rearrangement and cognate studies (8) Observation of the acid-catalyzed hydroxylation of phenylazopyridine to p-hydroxyphenylazopyridine and the proposal of an SNAr mechanism with formation of an intermediate hydrazo species in the reaction. (9) First study of benzidine type rearrangement-disproportionation of phenylhydrazopyridine in acid media. (10) Proposal of a A [Formula: see text] B [Formula: see text] C [Formula: see text] D type reaction profile for the consecutive hydroxylation[Formula: see text]disproportionation processes of phenylazopyridine in aq H2SO4. (11) Proposal of 10-π and 14π-electron electrocyclic processes in the benzidine type rearrangement-disproportionation of phenylhydrazopyridine. (12) Identification and structural elucidation of a dimer formed from phenylazopyridine as a minor product and proposal of a reaction mechanism. C. Facile acid-catalyzed demethylation via SNAr/A-SE2 mechanisms and studies of tautomerism (13) Observation of an abnormally facile acid-catalyzed cleavage (demethylation) of 4-methoxyphenylazopyridine via an SNAr mechanism. (14) Observation of two reaction pathways, SNAr and A-SE2, for the consecutive demethylations of 3,4-dimethoxyphenylazopyridine, with rate constant ratio of 7 000:1 favoring the SNAr process. (15) Quantitation of the tautomeric and protonation equilibria of 4-hydroxyphenylazopyridine, produced in (13). D. A new solvent polarity scale, molecular switches, and molecular electronics (16) Establishment of a π*azo solvent polarity scale based on solvatochromism of a series of azomerocyanine molecules ("Buncel's dye"). (17) Some glimpses are presented of current forays into molecular electronics, as emanating from the above studies: (a) spiropyran (SP) <> merocyanine (MC) thermo- and photochromic "molecular switch" systems; (b) synthesis and characterization of azo-functionalized star-burst dendrimers with photoswitchable properties and potential applications in optical data storage systems, holographic gratings, and drug delivery systems as host molecules.Key words: Wallach rearrangement, benzidine disproportionation, azoarenes, azoxyarenes, dendrimers, hydrazoarenes, dendrimers, solvatochromism, photochromism, thermochromism, spiropyran-merocyanine molecular switch.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,001 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,002 | 0,002 |
| Science ouverte | 0,001 | 0,001 |
| Intégrité de la recherche | 0,002 | 0,002 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,040 | 0,013 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».