The highly stereoselective synthesis of 3-methyl-l-halogenoallenes, 3-tert-butyl-l-halogenoallenes, and 1,3di-iert-butylallene is described. The R absolute configuration is assigned to the levorotatory halogenoallenes by relating them to alienes of known configurations. The configurational assignments are in agreement with (vacuum) circular dichroism data for the tert-butylallenes. The obtained results are used to clarify the hitherto existing confusion in the literature concerning absolute configurations of chloroand bromoallenes. Further, the signs and magnitudes of the ligand specific parameters for the halogens in the chirality functions approach, used to predict optical rotations of alienes, are discussed. The literature parameter for chlorine is revised and adequate numerical values for those of bromine and iodine are proposed.Recently, a synthetic route to optically active 3phenyl-1-halogenoallenes 1 and 21-halogeno steroidal alienes 2 of high enantiomeric purity has been described.2,3The present investigation demonstrates the utility of the method to obtain optically active 3-alkyl-1-halogenoallenes, viz., 3-tert-butyl-l-halogenoallenes 3a-c and 3-methyl-lhalogenoallenes 4b and 4c. These compounds, together with 1,3-di-tert-butylallene 3d, are very interesting from a theoretical point of view, particularly in relation to theoretical treatments of optical rotations of alienes.4,5

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Photoelectron (PE) as well as near-and vacuum-ultraviolet (300-1 50 nm) absorption and circular dichroism (CD) spectra of the tert-butylallenes (CH,),CCH=C=CHX (X = C(CH3),, C1, Br, I) are reported. The emphasis of the work is on the excited states and electronic structures of the allenes. In the PE spectra interactions between the substituents across the allenic C%=C system are observed. These can be rationalized in terms of Coulombic field effects and "hyperconjugation". Effects of vibronic coupling observed in the PE spectra are discussed qualitatively. By the combined use of absorption and CD spectroscopy, a large number of excited states resulting from valence-shell and Rydberg transitions are observed. The assignments of Rydberg states rely essentially on the absorption spectra using ionization energies from the PE spectra. Referring to the hydrocarbon as a representative of the allene chromophore, the sequence of excited states resulting from intravalence e -e (HOMO -LUMO) transitions is found to be lA2 < 'BI < 'B2 < 'A,. The intravalence excited states of the halogenoallenes originating with the two highest energy orbitals can be correlated with those of the allene chromophore. The two lowest energy excited states of chloro-and iodoallene are shown to have bent C=C=C geometries. In the CD spectra of the halogenoallenes low-energy excited states are detected with the corresponding electronic transitions terminating at the antibonding C-X u orbitals ( u *~-~) and u*c-x comprising halogen d atomic orbitals.

Es werden die Darstellung und die optische Spaltung von Allencarbonsauren 1 beschrieben. On the Stereochemistry of Allenes, I . -Preparation and Optical Resolution of a Series of Allenecarboxylic AcidsThe preparation and the optical resolution of some allenecarboxylic acids 1 are reported.Ausgangspunkt fur die vorliegende Arbeit war die vor kurzem publizierte Theorie der Chiralitatsfunktionen1.2). Neben algebraischen Beziehungen, d. h. streng gultigen