Elisabeth Langer

Zur frage transanularer II-II-wechselwirkungen im [2.2]metacyclophan, [2.2]Paracyclophan und 2,2′-spirobiindan

Zusammenfassung Aus dem Quotienten der beiden Dissoziationskonstanten ( K 1 / K 2 ) von [2.2]Metacyclophan-bis-chromtricarbonyl (9·0 ± 1·9) wurde geschlossen, das zwischen den beiden Benzolringen keine transanularen II-II-Wechselwirkungen bestehen. Die entsprechenden Werte fur die Bischromtricarbonyl- komplexe von 2,2′-Spirobiindan und [2.2]Paracyclophan sind 8·0 ± 1·5 bzw. 10 4 . Diese Ergebnisse wurden durch IR-spektroskopische Daten der CO-Frequenzen der Cr(CO) 3 - Komplexe von [2.2]Metacyclophan und einigen Derivaten, von 2,2′-Spirobiindan und [2.2]Paracyclophan erhartet. Fener wird gezeigt, dass UV-spektroskopische Studien an Tetracyanoathylen-komplexen von Aromaten im Hinblick auf transanulare II-II-Wechselwirkungen nicht relevant sind.

Zur theorie der chiralitätsfunktionen—III: Chiralitätsbeobachtungen im absorptionsgebiet von [2.2]metacyclophanen

Zusammenfassung Die Unzulanglichkeit von Naherungsanaitzen zur Beschreibung von Molrotationen optisch akriver 4,14-homodisubstituierter [2.2]Metacyclophane gibt Anlass zur Analyse ihres Circulardichroismus (CD). Die aus den langstwelligen elektronischen Ubergangen ( 1 L b - bzw. 1 W-Bande) erhaltenen Chiralitatsbeobachtungen zeigen an allgemeinen gute Ubereinstimmung mit den verwendeten Naherungsfunktionen. Im Gegensatz dazu ist eine adaquate Beschreibung energetisch hoherer Ubergange nicht mehr moglich. Diese Nichtaquivalenz von Observablen der optischen Aktiviat im Rahmen der Naherungsansatze erlaubt eine Lokauslisierung der zwischen berechneten und gemessenen Molrotationen gefundenen Diskepanzen auf bestimmte elektronische Ubergange. Eine physikalische Deutung ist im Hinblick auf Wechselwirkingen der beiden aromatischen Chromophore in hoher angeregten Zustǎnden moglich.

The ring current in π-arene tricarbonylchromium(0) complexes (benchrotrenes)

Abstract An investigation of the ring current contribution to the 1H NMR chemical shifts of benzene tricarbonylchromium complexes (benchrotrenes) is presented. Appropriate model compounds are provided by the [2.2] metacyclophanes Ia–IIIa, [2.2]metaparacyclophane (IVa) and their respective tricarbonylchromium complexes Ib–IVb, in which the monitor protons are not directly attached but are in close proximity to the aromatic nuclei under consideration. The systems chosen permit a check to be made of geometry preservation on complexation, which is a necessary condition for a significant 1H NMR comparison of complexed and uncomplexed arenes. The evidence indicates that the ring current shielding in benzene tricarbonylchromium complexes is considerably reduced above the ring plane. Analogous results were obtained for the [2.2] paracyclophanes Va and Vb. The observations strongly favour the ring current disrupture hypothesis, which has been questioned recently.

Eine beziehung zwischen absoluter konfiguration und dem 1Lb-Cottoneffekt chiraler carbophane☆

Zusammenfassung Fur optisch aktive Carbophane wird ein Verfahren zur Korrelation des Vorzeichens des 1 L b -Cottoneffektes des Benzolchromophors mit dem Chiralitatssinn (der absoluten Konfiguration) angegeben. Die zur Anwendung der Sektorenregel notwendigen Voraussetzungen und Bedingungen werden diskutiert.

Synthesen 2-substituierter 3-Indol-alkansäuren

A synthetic approach to 2-alkoxycarbonyl-3-indolealkanoic acidsvia partial saponification of the corresponding diesters is presented. 2-Ethoxycarbonyl-3-indoleacetic acid as well as the homologous propionic and butyric acids may conveniently be prepared by this method. A different synthesis of 3-indoleacetic acids functionalized at position 2 can be accomplished by decomposition of ethyl diazoacetate in the presence of the indole derivative at elevated temperature. Cyclization of 2-hydroxymethyl-3-indoleacetic acid, thus prepared, yields the corresponding δ-valerolactone. With 1-acyl-indoles and ethyl diazoacetate addition of the carbene to the C-2=C-3 double bond prevails, resulting in the formation of cyclopropanecarboxylic esters.

Concerning the theory of chirality functions: Part I. Construction and discussion of chirality functions by means of [2.2] metacyclophanes

Abstract By means of [2.2]metacyclophane (skeleton symmetry C 2h ) the construction of qualitatively-complete chirality functions via the first and second “Naherungsansatze” is demonstrated. In this context, a detailed comment concerning the algebraic theory of chirality functions is given. As the first term of the chirality function (“abridged Ansatz”), both methods furnish a simple superposition rule (“quadrant rule”). The second component as deduced via the method of polynomials is of third degree in ligand specific parameters. A particular property of the second approximation method is derived. The consequences with respect to observables of the chirality phenomenon, in the case of the approximations being valid, are discussed.

Rotamere 2-Phenyl-1,3-dioxane

By means of dipole moment measurements, NMR-spectroscopical methods and force field calculations of o-, m- and p-substituted 2-phenyl-1,3-dioxanes a systematic study concerning the rotameric behaviour of the phenyl group was performed.In o-substituted 2-phenyl-1,3-dioxanes the preferred conformation of the phenyl ligand was found to be displaced about 60 degs. from thecisoid-bisectional conformer. Introduction of an additional substituent in the second o-position gives rise to a change in the rotameric state, the preferred conformation now being bisectional. In contrast, the barriers resisting rotation about the Car−C-2-bond in 2-phenyl-1,3-dioxane and its m- and p-substituted derivates turn out to be much lower. Thus at room temperature an ensemble of approximately bisectional rotamers exists.The conformations and rotational barriers determined are discussed in terms of non bonded and dipole-dipole interactions.

Anwendung derR-Wert-Methode auf isokonformere Cyclohexane: Kernsubstituierte [2.2]Metacyclophane

The applicability of theLambert-Buys-Criterion (R-Value-Method) is tested for the ten-membered ring of [2.2]metacyclophane. The torsional angles thus obtained from the vicinal proton spin coupling constants are in accordance with X-ray data and recent force field calculations. Consequently, further investigations could be performed regarding the changes of the basic geometry in substituted [2.2]metacyclophanes. Fourteen derivatives with different substituents and substitution patterns were studied and their conformational changes are discussed.

Isomerisierung und Ringinversion von Tribenzaspiro[5.5]undecaphanen

For the two possible ring inversions in tribenzaspiro[5.5]undecaphanes—corresponding to the isomerizations7→9 and9→7 resp.—no mutual influence is found. Thus the degenerate isomerizations (“topomerizations”)7→7 and9→9 can proceedvia two consecutive (non-concerted) reversals. A ring inversion path similar to that for [2.2]metacyclophane (1) is postulated. The considerable ease of the isomerization of9 as compared to1 can be understood on the basis of thermodynamic arguments.Moreover it is confirmed that the free enthalpy difference ΔG360=3.84 kcal/mol of7 and9 at equilibrium originates almost entirely from the different stabilities of boat and chair shaped benzene rings.These conclusions are drawn from a kinetic study of the thermal isomerization of9 and equilibration experiments in comparison with the corresponding data of1. The activation parameters for the process9→7 are: ΔG360isomA≠=26.52 kcal/mole, ΔHisomA≠=25.35 kcal/mole, ΔSisomA≠=−3.28 cal/deg·mole (isomerization) and ΔG360invA≠=27.03 kcal/mole, ΔHinvA≠=25.35 kcal/mole, ΔSinvA≠=−4.67 cal/deg·mol (ring reversal); the corresponding data for the degenerate isomerizations of7 and9—identical with those for the ring reversal in7—were deduced to be ΔG360invB≠=30.87 kcal/mole, ΔHinvB≠=27.50 kcal/mole and ΔSinvB≠=−9.5 cal/deg·mole.

Zur Theorie der Chiralitätsfunktionen

The Algebraic Theory of Chirality Functions is derived by means of exclusively qualitative considerations. Hence, the significance of quantitative results is questionable. Moreover the construction of “Näherungsansätze” (”Approximation-Ansatz”), which may be interpreted as semiempirical methods, is achieved on the basis of plausibility and mathematical simplicity. Since physical arguments are not included, the consistency or inconsistency of “Näherungsansätze” with experimental results do not justify direct physical conclusions.