Tove Thomasen

New methods for the accurate determination of extinction and diffusion coefficients of aromatic and heteroaromatic radical anions in N,N-dimethylformamide

Abstract Two electrochemical methods are presented that allow an easy access to highly accurate UV-visible spectra of aromatic and heteroaromatic radical anions with life times longer than 50 s in N , N -dimethylformamide. The uncertainty on the extinction coefficients obtained is estimated to be as low as 5% which is a significant improvement in accuracy compared with other methods. The study has involved the radical anions of benzophenone, fluorenone, 1,4-naphthoquinone, anthraquinone, 1,2-benzanthraquinone, (E) -stilbene, anthracene, 9,10-diphenylanthracene, fluoranthene, perylene, benzonitrile, p -tolunitrile, 1,4-diacetylbenzene, 1,4-dicyanobenzene, 9,10-dicyanoanthracene, (E) -azobenzene, ( E )-4-methoxycarbonylazobenzene, quinoxaline and phenazine. The first method takes advantage of a galvanostatic generation of the radical anions from the parent compounds combined with the recording of the absorbance at specific wavelengths by means of a so-called dip probe. The second technique described is based on the continuous and complete electroreduction of the aromatic compounds in an efficient electrochemical flow cell placed just ahead of a quartz cuvette in a traditional diode-array spectrometer. The successful strategy of combining a galvanostatic generation of aromatic radical anions with the measurement of a characteristic physical property has also been employed in the determination of diffusion coefficients. The recording device is here a rotating disc electrode.

Acetylenes from roots of Eryngium bourgatii

Abstract The roots of Eryngium bourgatii afforded, in addition to falcarinone, falcarinolone, falcarinol and scopoletin, the Z and E isomers of 6-pentyl-2-[2-oxo-butin-(3)-yliden]-tetrahydropyran. The new Z isomer of 6-pentyl-2-[2-oxo-butin-(3)-yliden]-tetrahydropyran is unstable as it easily converts into the E isomer.

Thiophene derivatives from Echinops species

Abstract Roots and green parts of 16 Echinops species were examined by GC-MS for their content of thiophenes. Thiophenes were detected only in the roots. From E. bannaticus and E. ritro two thiophene dimers known as cardopatine and isocardopatine were isolated. These dimers have previously been isolated from Cardopatium corymbosum , but are reported here from Echinops species for the first time.

A chalcone and other constituents of Bidens tripartitus.

Abstract Green parts and flower heads of Bidens tripartitus were examined separately. Three polyacetylenes, two thiophene derivatives, linoleic acid, eugenol, ocimene and 2′-hydroxy-4,4′-dimethoxychalcone were isolated and characterized. Traces of the highly unstable cosmene were also detected.

Acetylenes from the roots of Solidago species

Abstract Roots of six Solidago species were examined for their content of acetylenes. The E and Z isomer of dehydromatricaria ester, ( Z , Z )-matricaria ester, ( Z )-dehydromatricaria lactone and a C 16 -acetylene were isolated and identified. The Z and E isomer of dehydromatricaria lactone were furthermore produced by oxidation of 2,4-hexadiynyliden-1,6-dioxaspiro-[4.4]nona-2, 8-dien-4-ol with activated MnO 2 .

Polyacetylenes from the fruits of Hedera helix

Abstract The fruits of Hedera helix afforded, in addition to the known polyacetylenes falcarinone and falcarinol, a polyacetylenic epoxide closely related to panaxydol. The structure of the epoxide was determined by spectral methods to be ( Z )-9,10-epoxy-1-heptadecene-4,6-diyn-3-one.

Polyenes from Centaurea scabiosa

Abstract The flower heads of Centaurea scabiosa afforded in addition to compounds previously isolated from this plant five homologous isovalerate tetraene esters, with chain length varying from C 14 to C 18.

Polyacetylenes from Dahlia species

Abstract Roots, leaves and flowers of Dahlia australis , one D. coccinea strain, and two strains of D. sherffii were examined. Twenty-six polyacetylenes of known structures together with cosmene and eugenol were isolated and characterized.

Thiophene derivatives and polyacetylenes fromDahlia tubulata

Abstract Roots, green parts and flower heads of Dahlia tubulata were examined separately. Nine polyacetylenes and five thiophenes of known structures were isolated and characterized. Four of the five isolated thiophenes are present only in very small amounts.