2589-76-6Relevant articles and documents
Alkylated phenol series in lacustrine black shales from the Noerdlinger Ries, southern Germany
Barakat, Assem O.,Baumgart, Susan,Brocks, Peter,Scholz-Boettcher, Barbara M.,Rullkoetter, Juergen
, p. 987 - 994 (2012/11/06)
Several series of alkylated phenols were detected for the first time in the extractable bitumens of organic matter-rich sediments from the Noerdlinger Ries (southern Germany). Most abundant and significant constituents comprise those with n-octadecyl, n-eicosanyl, phytanyl, and iso-pentadecyl and anteiso-pentadecyl substituents. The structures of these compounds are suggested from mass spectrometric and retention time data and coinjection with synthetic standards. Diagenetic alteration of phenolic algal lipids is suggested as a possible way to the formation of these compounds in the Noerdlinger Ries sediments. Copyright
Selectivity in the photodimerization of 6-alkylcoumarins
Yu, Xiuling,Scheller, Dieter,Rademacher, Otto,Wolff, Thomas
, p. 7386 - 7399 (2007/10/03)
Coumarin and 6-alkylcoumarins (alkyl = C1 to C16) were photodimerized in homogeneous solvents differing in polarity and in aqueous micellar solutions. The four possible photodimers, syn head-to-head (hh), anti head-to-head, syn head-to-tail (ht), and anti head-to-tail, were identified through a combination of X-ray analysis and NMR spectroscopy. In 6-methylcoumarin the concentration-corrected dimerization (quantum) yield increases with decreasing concentration of the educt; anti- hh was formed exclusively in nonpolar solvents and upon triplet sensitization and was the main product under all conditions except for ionic micellar systems, which direct to preferred syn-hh dimerization. Long alkyl substituents, however, lead to anti-hh in polar solvents and in micelles, too. Predominating ht dimer formation was observed for nonsubstituted coumarin in polar solvents only. Thus, syn/anti and hh/ht selectivity can be steered by varying the 6-alkyl substituent. Syn- hh photodimers of 6-methylcoumarin can be photochemically split into the monomers; they partly proved thermally unstable against acids, bases, methanol, and on SiO2 surfaces.
Tilt Angle Variation as a Function of Chain Length and Temperature in the Smectic C Phases of p,Alkoxyphenyl-p,Alkoxybenzoates
Heinrich, B.,Guillon, D.
, p. 21 - 44 (2007/10/02)
The variation of the tilt angle with temperature in the smectic C phase has generally been shown to be non-existent or very slow for compounds or mixtures with the nematic-smectic C transition, while in the case of systems with the smectic A-smectic C transition, a relation between the steepness of this variation, near the transition, and the width of the smectic A domain has been observed.In this work, the variation of tilt angle in the smectic C phase is described for p-alkoxyphenyl-p-alkoxybenzoate homologous series, for which the evolution of polymorphism can be controlled systematically, by varying stepwise the length of the aliphatic chains, and for which large domains can be obtained for each type of phase sequence, nematic-, smectic A- and isotropic-smectic C.After completing the discussion made previously on the incidence of chain length on polymorphism, we confirm that the variation of tilt angle with temperature is slowest for compounds with intermediate chain lengths corresponding to the largest smectic A temperature range; this variation becomes continuously steeper when the smectic A domain becomes narrow.In addition, we show that the same description can be extended to the other types of phase sequences, by using the hypothesis of a virtual smectic A-smectic C transition above the observed nematic- or isotropic-smectic C transition.In fact, short chain lengths for homologues with a nematic/smectic C transition, or long chain lengths for homologues with an isotropic/smectic C transition, lead to an increase of the tilt angle at the phase transition and to a decrease of the amplitude of its variation with temperature; in our description, this behaviour corresponds to an increase of the temperature range between the real and virtual transitions.As a consequence, the homologues with very short and very long chain lengths show a quasi temperature-independent tilt angle, while the other homologues present a tilt angle variation similar to that observed for compounds exhibiting a smectic C/smectic A transition.This feature indicates that there is no need to distinguish between different types of smectic C phase.
