Structure and reactivity of polycyclic cross-conjugated π-electron systems

Hafner, K.

doi:10.1351/pac197128020153

Cited by 71 publications

(23 citation statements)

References 2 publications

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“…Upfield shifts of 15.7 and 9.9 p.p.m. spectra ( Figure 5) as diatropic and paratropic, respectively, in accord with theoretical calculations 15 and earlier findings for aceheptylene (9) 16 . In order to determine how much of these upfield shifts can be attributed to ring current shielding, the structural features of 2 are added stepwise to naphthalene.…”

Section: The Ring Current Effectsupporting

confidence: 91%

RESULTS OF CARBON-13 NMR SPECTROSCOPY IN THE FIELD OF CYCLIC CONJUGATED Π-Electron SYSTEMS

Günther

Schmickler

1975

The Chemistry of Nonbenzenoid Aromatic Compounds –II

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The theoretical basis for the interpretation of 13 C chemical shifts is reviewed briefly. Possible ring current contributions to the shielding of the 13 C nucleus are discussed in detail with examples from the field of polycyclic nonbenzenoid π-systems and bridged annulenes. The fingerprint nature of 13 C n.m.r. data is stressed and the significance of σ-bond structure is demonstrated for bridged [14]annulenes and related compounds. Pyrene and the two isopyrenes dicyclopenta [ef,kl]heptalene and dicyclohepta [cd,gh]pentalene serve to illustrate typical features of 13 C n.m.r. spectra of alternating and non-alternating nsystems. Finally, the sensitivity of 13 C n.m.r. for the detection of valence isomerizations is. exemplified with results obtained for 11,11-disubstituted 1,6-methano-[ 10]annulenes.

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Section: The Ring Current Effectsupporting

confidence: 91%

RESULTS OF CARBON-13 NMR SPECTROSCOPY IN THE FIELD OF CYCLIC CONJUGATED Π-Electron SYSTEMS

Günther

Schmickler

1975

The Chemistry of Nonbenzenoid Aromatic Compounds –II

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“…This x-electron system is therefore assumed to be relatively unstable. This result is in excellent agreement with the REPENprediction (0.138), as well as with magnetic and u.v.-spectral properties of this compound (29).…”

Section: An Extension Of the Hiickel4n + 2 Rulesupporting

confidence: 88%

An Extension of the Hückel 4N + 2 Rule to Polycyclic Non-alternant Conjugated Hydrocarbons

Kruszewski¹,

Krygowski²

1975

Can. J. Chem.

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JERZY KRUSZEWSKI and TADEUSZ MAREK KRYGOWSKI. Can. J. Chem. 53,945 (1975) A general rule of aromatic stability of non-alternant polycyclic conjugated hydrocarbons has been detailed and using aromatic stability indices, corroborated. The n-electron system is said t o be relatively more stable if the difference between number of 4N + 3-type rings minus number of 4 N + 1-type rings is 0 or divisible by 4 . If not, the system is assumed t o be relatively unstable. The presence of benzene rings does not affect the rule. A further extension for intramolecular H-bonded systems is also suggested. The rule suggested permits prediction of substituent effects on stability as well as the ionic form being most stable if the rule is not fulfilled.JERZY KRUSZEWSKI et TADEUSZ MAREK KRYGOWSKI. Can. J. Chem. 53,945 (1975). On a dCveloppC une regle gCnCrale permettant d'kvaluer la stabilite aromatique des hydrocarbures polycycliques conjugues mais non alternants; cette regle a Ct C corroboree en faisant appel aux indices de stabilitk aromatique. On dit gCnCralement que le systeme d'klectrons n est relativement plus stable si la diffkrence entre le nombre des cycles du type 4 N + 3 moins le nombre des cycles du type 4 N + 1 est 0 ou divisible par 4 . Si tel n'est pas le cas, on fait I'hypothtse que le systeme est relativement instable. La presence de noyaux benzkniques n'affecte pas cette rigle. On suggere aussi une autre extention pour les systemes contenant des ponts hydrogkne intramolCculaires. La rkgle suggCrCe permet aussi de prkdire l'effet des substituants sur la stabilitk de mEme que la forme ionique est la plus stable si la regle n'est pas suivie.[Traduit par le journal]The Huckel4N + 2 rule (1) is one of the best known and most useful rules for predicting the aromatic stability of monocyclic n-electron systems (2). An extension of this rule to polycyclic conjugated hydrocarbons has not been successfully developed. Some indirect applications, taking into account only peripheral n-bonds of these systems, led to rather good results (3), but most often in the case of alternant systems. Recently a number of authors have reviewed the problem of aromatic stability (see e.g. refs. 4-8, 11-24, 35) and have suggested various quantitative measures of "aromaticity". The most advantageous seem to be those coming from quantum chemical calculations like the Hess-Schaad REPE (1 3) (Resonance Energy per Pi Electron) or other (7, 10, 11,14) estimates of resonance energy. However, these calculations cannot always be carried out especially by those 'Visiting Professor at the Department of Chemistry, University of Guelph, Guelph, Ontario, NIG 2W1. concerned with the practical aspects of organic chemistry such as synthesis; moreover, the quantum mechanical calculations are not always sufficiently reliable. It is clear that a simple rule as a qualitative guide to aromatic stability is needed in the area of non-alternant polycyclic conjugated hydrocarbon chemistry.The main purpose of this paper is t o present an attempt to extend the Huckel4...

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“…Mit den aus Arylazomalondialdehyden 1 und Cyclopentadien nunmehr leicht zuganglichen l-Dialkylamino-l,2-dihydro-2-pentalenon-phenylhydrazonen 12 wird der Umfang der bisher bekannten Pentalenderivatel3. [18][19][20][21][22] um eine Verbindungsgruppe erweitert, aus der einfach substituierte Pentalene darstellbar sein sollten. Die Verwendung des Fluormalondialdehyds als Reaktionspartner des Cyclopentadiens hat bereits zur Darstellung von l-Dimethylamino-2-fluor-2,3-dihydropentalen gefiihrt 23).…”

Section: Reaktion Mit Cyclopentadienunclassified

Synthesen mit substituierten Malondialdehyden, XIII¹⁾ Die Kondensation von Arylazomalondialdehyden mit Fluoren, Inden und Cyclopentadien

Reichardt

Miederer

1973

Justus Liebigs Ann. Chem.

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Durch Kondensation der Arylazomalondialdehyde 1 rnit Fluoren und Inden werden die Dikondensationsprodukte 3 und 8 erhalten, die sich rnit Basen zu blauen, anionischen Kohlenstofftrimethin-Farbstoffen deprotonieren lassen. -Mit Cyclopentadien reagieren die Dialdehyde 1 in Gegenwart sekundarer Amine zu den l-Dialkylamino-l,2-dihydro-2-pentalenonphenylhydrazonen 12a-e, deren Struktur u. a. durch das 1H-NMR-Spektrum einer 15N.markierten Verbindung gesichert wird. Syntheses with Substituted Malondialdehydes, XI11 l). -The Condensation of Arylazomalondialdehydes with Fluorene, Indene, and CyclopentadieneCondensation of arylazomalondialdehydes 1 with fluorene and indene affords the dicondensation products 3 and 8, which are deprotonated by bases to blue, anionic carbon trimethine dyes. -The dialdehydes 1 react with cyclopentadiene in presence of secondary amines to give 1 -dialkylamino-l,2-dihydro-2-pentalenone phenylhydrazones 12a -e, the structure of which is proved by the 1H-NMR spectrum of a I5N-labeled compound.Substituierte Fulvene erhalt man nach ThieZe3) durch basenkatalysierte Kondensation von Cyclopentadien rnit Aldehyden oder Ketonen. Auch das unsubstituierte Fulven ist auf diesem Wege aus Cyclopentadien und Formaldehyd z~ganglich4~5).Nachdem wir gezeigt haben I), daB aliphatische Dialdehyde wie die Arylazomalondialdehyde rnit 1,4-Diketonen zu l-Acyl-3-arylazo-6-hydroxy-6-alkylfulvenen kondensieren, wurde nun gefunden, da13 Arylazomalondialdehyde auch mit Cyclopentadien oder seinen Benzoderivaten Inden und Fluoren zu substituierten Fulvenen reagieren. Reaktion mit FluorenRuhrt man Phenylazomalondialdehyd (1 a) rnit Fluoren in Dimethylsulfoxid/ Kalium-tert.-butylat mehrere Tage bei Raumtemperatur, so entsteht eine tiefblaue Reaktionslosung, aus der nach Zusatz von Wasser in 85 proz. Rohausbeute eine orange-

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Structure and reactivity of polycyclic cross-conjugated π-electron systems

Abstract: Abstract

Cited by 71 publications

References 2 publications

RESULTS OF CARBON-13 NMR SPECTROSCOPY IN THE FIELD OF CYCLIC CONJUGATED Π-Electron SYSTEMS

RESULTS OF CARBON-13 NMR SPECTROSCOPY IN THE FIELD OF CYCLIC CONJUGATED Π-Electron SYSTEMS

An Extension of the Hückel 4N + 2 Rule to Polycyclic Non-alternant Conjugated Hydrocarbons

Synthesen mit substituierten Malondialdehyden, XIII¹⁾ Die Kondensation von Arylazomalondialdehyden mit Fluoren, Inden und Cyclopentadien

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Structure and reactivity of polycyclic cross-conjugated π-electron systems

Abstract: Abstract

Cited by 71 publications

References 2 publications

RESULTS OF CARBON-13 NMR SPECTROSCOPY IN THE FIELD OF CYCLIC CONJUGATED Π-Electron SYSTEMS

RESULTS OF CARBON-13 NMR SPECTROSCOPY IN THE FIELD OF CYCLIC CONJUGATED Π-Electron SYSTEMS

An Extension of the Hückel 4N + 2 Rule to Polycyclic Non-alternant Conjugated Hydrocarbons

Synthesen mit substituierten Malondialdehyden, XIII1) Die Kondensation von Arylazomalondialdehyden mit Fluoren, Inden und Cyclopentadien

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Synthesen mit substituierten Malondialdehyden, XIII¹⁾ Die Kondensation von Arylazomalondialdehyden mit Fluoren, Inden und Cyclopentadien