Aromatization ethylene bridge

Fits of Eq. (9.43) to the experimental data typically yield an effective activation energy of about 230kJ/mol, which is consistent with the activation energy for rupturing an ethylene bridge between aromatic rings [41],... 

Closely related structurally to stilbenes are a class of compounds containing one or more ethylenic bridges between aromatic or heteroaromatic rings, exemplified by... 

There are several limitations on these methods with regard to the heteroatom involved. Reaction of the tin heterocycle with NBS results in cleavage of the aromatic-tin bonds to give o,o -dibromobibenzyl (81). Reaction of the tin heterocycle with DDQ resulted only in products of heteroatom elimination (81). Attempts to generate a silicon heterocycle with a functional group on the Si atom have failed to produce the unsaturated system (XVII). Dehydrobromination reactions of the silane afford highly colored reaction products but no isolable identifiable monomer. It is probable that the dehydrobromination reaction occurs not only at the ethylene bridge but also by transannular elimination. 

It is probable that 1,4-elimination is a characteristic of compounds that exhibit the folded-boat conformation and not to any intrinsic aromaticity of the RaM cation. The decrease in 1,4-elimination for (XXVIII) in the series Si to Sn may be due to either a flattening of the tricyclic ring system or lengthening of the M—C bond, either of which increases the distance between the heteroatom substituent and the ethylene bridge. 

This was the first theory proposed and fitted in well with the majority of results. There can be no doubt that the aromatic ring, phenol, and the nitrogen groups are all important, but there is some doubt as to whether the ethylene bridge is important, since there are several analgesics which lack it (e.g. fentanyl). 

We have observed additionally the wider resonances -125 ppm (AV / 4 kHz) assigned to two (of four) protons of the ethylene bridge, and a very broad line at -405 ppm (AV /2> 10 kHz) of the iminc protons. The latter signal was detected for all complexes at approximately the same field position. The resonances of the 3 and 6 aromatic protons of complex 2 arc masked by those of the residual protons of watcr-d and DMSO-d, The "H spectrum of complex 5 displays the peaks of the 3 and 6 dcuierons at 2,0 and -1.9 ppm. respectively [70]. Some spectral data for other mangancse(salcn) complexes arc collected in Table I. 

Protriptyline is a dibenzocycloheptriene TCAthat differs from the other tricyclics by having an unsaturated ethylene bridge joining the two aromatic rings and a secondary aminopropyl side chain (Fig. 21.8). Protriptyline is completely absorbed from the Gl tract and slowly eliminated. Its pharmacokinetics are shown in Table 21.3. Metabolism data are limited for protriptyline, but it is most likely to be metabolized via the same pathways as the other TCAs are (Table 21.2). Very little drug is excreted in the feces via the bile. 

Initially, a series of soluble, highly isospecific catalysts were developed for propylene polymerization [168]. These materials are zirconium, titanium, or hafiiium based metallocenes, such as racemic 1,1-ethylene-di-ri -indenylzirconium dichloride. The term metallocene applies to complexes of transition metals sandwiched between two aromatic rings, usually two cyclopentadienyl. They are rigid structures, due to ethylene bridges between the two five-membered rings. Syntheses of these compounds yield racemic mixtures of two enantiomers. Both produce isotactic polypropylene ... 

In this work, a series of PUs based on DBDI were prepared. They presented some specific features due to the diisocyanate structure [320]. Thus, when subjected to the photo-degradation process, the PUs based on DBDI showed a lower yellowing tendency than those based on MDI. This could be explained by the particular behaviour of the ethylene bridge between the two aromatic rings against the photo-degradation... 

Over the last 100 years, the grapevine Vitis vinifera L. (Vitaceae), the primary source of wine, has been the subject of numerous chemical studies. While stilbenoids are found in a number of plant species [19], grapes and related products are the most significant dietary source of these substances [20]. Stilbenoids are non-flavonoid polyphenols with an essential structural skeleton of two aromatic rings joined by an ethylene bridge (C6-C2-C6). Over 1,000 stilbenoids have been... 

Pyrene (32), a polycyclic aromatic hydrocarbon with four rings, can be seen as comprising varied subunits an ethylene-bridged [14]annulene, four fused benzene rings, two fused naphthalenes, a biphenyl or a phenanthrene. It s enthalpy of formation is 225.7... 

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