Christine Krieger

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.

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.

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.

Darstellung, chiroptische eigenschaften und absolute Konfiguration von 4,14-disubstituierten [2.2]Metacyclophanen

Resolution of [2.2]metacyclophane-4,14-dicarboxylic acid (2) was achieved by crystallization of its (+)- and (−)-α-phenylethylamine salts. Chemical correlation with (−)-(S)p-[2.2]metacyclophane-4-caboxylic acid (−)-11via its monobromo derivative (−)-8 established the absolute configuration of the dicarboxylic acid as (−)-(S)p-2. The key compound (−)-8 was prepared by partial lithiation and subsequent carboxylation of 4,14-dibromo[2.2]metacyclophane (1) and resolution with (−)-phenylethylamine.Recently proposed rules correlating the absolute configurations of planarchiral compounds with theirCD-spectra are discussed and a comparison of the chiroptical properties of 4,14-di- and 4-mono-substituted [2.2]metacyclophanes is presented.

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.

Zum rotameren Verhalten des Phenyl- und Phenyltricarbonylchrom-liganden in 2-substituierten 1,3-Dioxanen: Ein Vergleich

Dipole moment measurements, NMR-spectroscopical methods and dipole-dipole interaction calculations applied to 2-benchrotrenyl-1,3-dioxanes and a comparison with o-substituted 2-phenyl derivatives furnish evidence, that in both cases the rotameric state is mainly determined by the steric demand of the substituent being attached to phenyl: the declination angle (π) of the Cr(CO)3-group from the bisectional cisoid relation (with respect to H on C-2) is identical with that for the ortho substituent and amounts to about 60 degs. The influence of the Cr(CO)3-fragment on the conformational behaviour of the benzene moiety in geminal 2,2-disubstituted derivatives is consistent with these results: the assumption of an axial and gonal conformation for the phenyl ring, which had recently been established for 2-alkyl-2-phenyl-1,3-dioxanes, is no longer valid for the 2-alkyl-2-phenyltricarbonylchromium compounds.