Phenyl conjugation

Another instructive example is provided by a series of a-phenyl-a,P-dibromo-phosphonates 170, 171, 172. While the phosphonate dianion 170 fragments instantaneously at room temperature with formation of the POf ion (see also Sect. 4.1.3), the analogous reaction of the phosphonic monoester anion 171 leading to methyl metaphosphate 151 requires more drastic conditions and is at least 1000 times slower the diester 172 is essentially stable under the reaction conditions described for 171 addition of triethylamine leads to slow demethylation H0). The behavior of 171 contrasts with that of simple (3-haloalkylphosphonic monoesters which merely eliminate HHal on treatment with bases94. Thus it is the possibility of formation of a phenyl-conjugated double bond which supports the fragmentation of 171 to olefin + 151. 

Satisfactory to good yields of adducts have been found for styrenes (Scheme 5, Y = phenyl), conjugated dienes (Y = vinyl), enamines (Y = NR2), and enol ethers (Y = alkoxy), particularly if they are... 

More recently, structurally related metabolites have been found in Mediterranean cephalaspideans, that is, phenyl conjugated trienones, lignarenones A (54) and B (55) in the Cylichnidae Scaphander lignarius,125 and polyenic pyridines in the Haminoeidae haminols A (56) and B (57) in Haminoea navicula, haminol C (58) in H. orteai 26 121 Haminols A (56) and B (57) also induce alarm response at concentrations of 0.3 and 0.1 mg, respectively. Thus, navenones and their structural congeners may serve as a communication tool to indicate the presence of predators. 

The integrated dose to a tissue over a 14-hour period (6-hour exposure, 8 hours following exposure) was calculated for benzene metabolites in Fischer 344 rats and B6C3Fj mice that were exposed to 50 ppm of radiolabeled (3H) benzene (Sabourin et al. 1988). The major metabolic products in rats were detoxification products that were marked by phenyl conjugates. In contrast, mice had substantial quantities of the markers for toxification pathways (muconic acid, hydroquinone glucuronide, and... 

Target Tissues. The model correctly described metabolic differences observed between mice and rats. For instance, mice metabolize benzene more efficiently than rats during and after a 6-hour inhalation exposure. After oral exposure, mice and rats metabolized doses of benzene up to 50 mg/kg in a similar manner. At oral doses above 50 mg/kg, rats metabolized more benzene than did mice on a per kg body weight basis. Similar results were seen with the excretion of individual metabolites. Excretion of major metabolites, the phenyl conjugates, was similar for both species for oral doses up to 20 mg/kg, after which rats produced more phenyl conjugates than did mice. After inhalation, mice produced more phenyl conjugates at all exposure levels compared to rats when normalized to body weight. For hydroquinone metabolites, however, mice produce far more after both oral and inhalation exposure than rats. For muconic acid, the model predictions indicate that after inhalation exposure, mice produced more than rats after oral exposure, the relative amount of muconic acid produced by the two species was similar. 

Species Extrapolation. The Medinsky model used species-specific information to outline the model parameters little extrapolation of information between mice and rats was required. Based on the parameters derived for mice, metabolism of benzene after inhalation by humans was simulated. The results indicate that at concentrations below 10 ppm, metabolism and formation of metabolites is linearly related to inhaled concentration, and that hydroquinone conjugates are the predominant metabolite. At concentrations above 10 ppm, the model predicts a change in the metabolic profile, with increased proportion of phenyl conjugates, associated with detoxification processes. 

Fig. 4.102 Enantioselective epoxidation of phenyl-conjugated olefins employing aldehyde and molecular oxygen as the oxidant.

Satisfactory to good yields of adducts have been found for styrenes [Eq. (21a), Y = phenyl], conjugated dienes (Y = vinyl), enamines (Y = NR2), and enol ethers (Y = alkoxy), particularly if they are unsubstituted at the 6-carbon atom to Y. Nonactivated alkenes react less satisfactorily. In the oxidation of anionized 1,3-dicarbonyl compounds (Table 11, numbers 1-8) at potentials between 0.6 and 1.4 V (SCE) and in the presence of butadiene, only the additive dimer LXII is obtained in the presence of ethyl vinyl ether only the disubstituted monomers LXVI or LXVII arise, but with styrene both types of products LXII and LXVI are formed. This result indicates that the primary adduct LXIII is oxidized rapidly between 0.6 to 1.4 V to the carbenium ion in the case of an ethoxymethyl radical (Y = OEt), and slowly in the case of an allyl radical (Y = vinyl). 

The fluorescence of nonconjugated acetylenes is weak ( = 0.009-0.014) [22], and the lifetime is about a few ns. Nonconjugated acetylenes have no appreciable phosphorescence, and their singlet-triplet absorption has not been characterized, while singlet-triple absorption spectra have been recorded for diynes, poliynes, and phenyl conjugated acetylenes, and triplet energies can be obtained from phosphorescence spectra [23]. 

J7-Chromene is characterized by the following H-NMR data 6 = 6.44 (2-H), 4.63 (3-H) and 3.36 (4-H) (CDCI3). 4i/-Chromenes absorb at 280 nm in the UV spectrum. They can be distinguished from 2//-chromenes, whose phenyl-conjugated double bond absorbs at longer wavelength ( 320 nm). 

Uan, T., and Yanagida, S. (2004) Phenyl-conjugated oligoene sensitizers for Ti02 solar cells. Chem. Mater., 16, 1806-1812. 

Phenyl-conjugated C=C bonds have a strong stretching band at 1625 cm" in CO or C=C conjugation, the band lies at 1600cm" Nonconjugated C=C bonds show bands at 1680-1620 cm" For olefins, a cis double bond in RCH=CHR lies at 1662-1653 cm" S and a trans double bond at 1678 1653 cm" Thus, trans-3-hexene-D-t/irco-l,2,5,6-tetrol has a band (Tipson and Cohen, 1966) at 1653 cm" A terminal exocyclic double bond, as in H2C=CRR, displays a band at 1658-1648 cm" and H2C=CHR displays one at 1648-1638 cm" ... 

However, 1-phenylpropene undergoes hydroboration at the C-1 position. This is not what one would expect based on the steric effect of a phenyl group. This is because of the combined effects of phenyl conjugation (-K) and methyl hyperconjugation (-tK), which act to decrease the amount of electron density at the C-2 position and to increase it at the C-1 position (Fig. 4.1) [6]. Evidently, these mesomeric effects are strong enough to override the steric effects of the phenyl group. 

Fig. 4.1 Diagram to show combined effects of phenyl conjugation (-K) and methyl hyperconjugation (+K) in 1-phenylpropene [6]...

Rotation of phenyl group out of the plane of n-electron cloud, which disrupts phenyl conjugation in cis-1-phenylpropene, is supported due to the greater hydroboration at the C-2-postion (17.5%), than in the tram isomer (3.2%). However, the rate-retarding steric effects of phenyl rotation prevail. 

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