Determination of the Configuration of Wine Lactone

The intense sweet and coconut-like smelling odorant 1 , named ‘wine lactone’, was isolated from different wine varieties. The chemical structure of this compound, which has not yet been detected in wine or a food, was identified by high-resolution mass spectrometry (HR-MS) as 3a,4,5,7a-tetrahydro-3,6-dimethylbenzofuran-2(3H)-one. For the evaluation of the configuration of wine lactone, stereochemically controlled syntheses were developed. All eight isomers were characterized by NMR, MS, IR, and CD measurements. The configuration of ‘wine lactone’ was in agreement with synthesized (3S,3aS,7aR)-enantiomer ( 1a ) on the basis of enantioselective GC. For this isomer, the lowest odor threshold (0.02 pg/1 air) was detected.     

Unimolecular Gas-Phase Oxidation of Terminal Hydroxy Groups in [FeO(CH2)nOH]+ Complexes (n = 2–8). A Case for O?H Bond Activation by Late Transition-Metal Ions. Preliminary Communication

In contrast to Fe⁺/diol complexes, gas-phase dehydrogenation of the corresponding Fe^II alkoxides, [FeO(CH₂)_nCH₂OH]⁺, is a highly specific process in the course of which oxidation of the terminal OH group takes place. Based on labeling studies, this is the exclusive mechanism for n = 2 and 3 (Scheme: path ); for higher homologues, as for example [FeOf(CH₂)₇CH₂OH]⁺, the labeling data demonstrate that an additional mechanism is operative, involving the dehydrogenation of internal positions of the alkyl chain (path ). The Fe⁺-mediated oxidation –CH₂OH → –CHO +H₂: constitutes one of the rare examples of O-H bond activation by late cationic transition-metal ions.     

Reflection groups and K-loops

The notion reflection group (, ) was introduced in order to give group theoretical characterizations of absolute planes. Here we consider reflection groups with midpoints and associate to each of them an incidence structure . Then is an incidence space which dimension can assume any value. The motion group together with the set of all reflections in points of a Euclidean or hyperbolic geometry are examples of reflection groups with midpoints. Furthermore the set can be turned into a K-loop. The precise results are summarized in the theorems at the end of the paper.Cordially dedicated to Sibylla Prieß on the occasion of her 60th birthdaySupported by the NATO Scientific Affairs Division grant CRG 900103.     

Reflection geometries over loops

We characterize right loops (L, +) without, respectively with an incidence fibration F from which one can derive a reflection or a point- reflection structure, respectively a reflection or a point- reflection geometry in the sense of [1].     

Near-rings (MDS)- and Laguerre codes

(MDS)- and Laguerre codes are closely related to geometry and can be used in order to construct certain finite incidence structures. Here we present some structure theorems on near rings, introduce the notion of a coding set of a near ring, which enables us to construct (MDS)-codes, and discuss the same problem for Laguerre codes. To find non trivial Laguerre sets in a near ring is much more difficult.Dedicated to Giuseppe Tallini on the occasion of his 60 th birthday     

1,1-Dicyano-2,2-diphenyl-1,2-dihydronaphthalene: photochromism and evidence for photochemically induced C[bond]CN bond cleavage

The photoreactions of the 1,1-dicyano-2,2-diphenyl-1,2-dihydronaphthalene (DHN-1) have been studied by photochemical techniques under various conditions at room temperature. A transient species, T(C), with a major maximum at 545 nm in the UV-visible spectrum, detected in small yield in polar aprotic solvents and in large yield in trifluoroethanol (TFE) and hexafluoropropan-2-ol (HFP), is assigned as a carbocation (1-cyano-2,2-diphenylnaphthalenium), which is generated photochemically by elimination of CN(-). The decay of T(C) was found to be a first-order process in HFP, in which the longest lifetime of 0.4 s was observed; in TFE, the carbocation decays on the ms timescale, while the shortest lifetime of 1 micros was found in ethanol. The yield of T(C) increases strongly upon addition of water to alcohols or acetonitrile, and remains substantial in the presence of large amounts of water (1-20 M). On addition of water to TFE or HFP, the lifetime of the carbocation becomes much shorter. This is supported by pulse-induced charge formation due to the carbocation and release of CN(-); the conductivity decay is related to the lifetime of the carbocation under selected conditions. In addition, a major irreversible and a minor thermally reversible photoprocess were spectroscopically observed in solvents of low as well as high polarity. The former photoproduct, absorbing below 300 nm, is tentatively ascribed to benzobicyclohexenes A produced by phenyl-vinylmethane rearrangement. In the latter process, a longer-lived benzoquinodimethane derivative B, having a maximum at 400-430 nm, is formed; this is related to ring opening and closure and represents a new example of photochromic ten-electron electrocyclisation. The distinct differences between the photochromism of DHN and that of dihydroazulene (DHA) stem mainly from stereoelectronic effects. This study, however, has also revealed that photochemically induced bond heterolysis and photochemical/thermal electrocyclisation, representing two basic processes of photochromism, may occur in one molecular unit.     

Surface selectivities in wet chemically modified PVC films. Influence of reaction conditions

Wet chemical modification reactions of PVC films in solvent/nonsolvent mixtures were performed. Three thiol compounds of different size and reactivity were used varying the solvent quality, temperature, and reaction times. The evolution of the concentration gradients within the films was studied using confocal Raman spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy. Surface selectivities were calculated and discussed in terms of the different relative reaction rate constants.