With benzene derivatives

The scheme shows that the influence of substituents on CH acidity in ethynylpy-razoles is not additive as compared with benzene derivatives (84IZV923), and its value depends, for each substituent, on the nature of other groups in different positions of the azole. [Pg.77]

Vinyldialkylsilanes and vinyltrimethylsilane having no chlorine atoms do not undergo alkylation with benzene derivatives in the presenee of aluminum chloride but vinylchlorosilanes react with benzene to give the alkylation products. The reaetivities of vinylchlorosilanes decrease in the following order vinyl(methyl)di-chlorosilane > vinyltrichlorosilane > vinyl(dimethyl)chlorosilane. [Pg.159]

Exchange Reactions with Benzene Derivatives. Preparation of 1 3 5-Tri-, 1 2 4 5-Tetra- and Pentadeuterobenzene. J. chem. Soc. [London] 1946, 239-... [Pg.178]

As predicted, in reactions of 3-diazopyrroles, 3-diazoindoles, and 4-diazopyrazoles with benzene derivatives, azolylidene 35 also reacted in its triplet state to give the parent heterocycle by abstraction-recombination processes. [Pg.88]

The aromatic complex can be a neutral t °-benzene derivative or an anionic ri -cyclopentadienyl ring. Substituents on these aromatic rings can greatly influence the effectiveness of these catalysts. For example, with benzene derivatives the unsubstituted benzene rings give lower ees and the use of hexamethylbenzene results in lower catalytic activities whilst the cumenyl or mesityl rings give optimum catalyst systems. The two types of chiral bifunctional hnkers that have been most practical are anionic ones based on monosulfonated diamines and amino alcohols. [Pg.16]

The latter three, (4)—(6), are utilized for qualitative elucidation of the observed ICD bands in signs, and the former three, (1)—(3), are successfully applicable for quantitative calculations of the observed ICD bands in both signs and magnitudes. The ICD of P-cyclodextrin complexes with benzene derivatives or azanaphthalenes162) has been analyzed by a molecular orbital calculation, using an approximation of PPP-type, which has been compared with the theoretical spectra calculated by using the CNDO/S-CI method on the basis of the MCD spectra 16S). [Pg.113]

Nitroalkenes react with benzene derivatives at low temperature in triflic acid to afford a-aryl ketones after quenching with methanol182,183 [Eq. (5.74)]. At higher temperature the 0-protonated oxime intermediate may react further to yield 4//-1,2-benzoxazines (see Section 5.14.1.3). a-Nitrocarbonyl compounds show similar characteristics as alkylating agents to yield oximes with the involvement of the tricationic intermediate 44.181... [Pg.556]

Reactions of benzene have already been mentioned. They have been studied mainly with benzene derivatives and we will not here give the complete story but will cite one pair of reactions both of which are reversible photochemically126... [Pg.55]

So far, only examples of A-D-D triplexes have been discussed. One example of an emissive A-D-D triplex was recently reported by Pac and co-workers [115]. Excited singlet 1,4-dicyanonaphthalene forms exdplexes with benzene derivatives whose emission is quenched by a variety of aromatic olefins. This quenching is accompanied by the appearance of new emissions at longer wavelengths which has been assigned to a A-D-IT triplex with e.g., A = 1,4-dicyanonaphthalene, D = benzene, D = 2-methylstyrene. [Pg.251]

The following aspects will be addressed. (1) Conjugated polymers with benzene-derived repeat units (section II) typical examples are the already mentioned poly-/>phenylene (PPP) 6,43 polyphenylene-vinylenes (PPV) 9,43 and polyphenyleneethinylenes (PPE) 25.44 Some typical questions are obvious how do the aromatic or olefinic units interact via the formal single bonds and how far does an extra charge or an excitation delocalize over the chain. (2) Large... [Pg.4]

Reactions of recoil halogens with benzene derivatives... [Pg.506]

Replacement of the —SO3H group by a hydrogen. With benzene derivatives, this is done by heating with water or steam and acid. (p. 762)... [Pg.810]

Since we introduced conjugate addition in Chapter 10, a number of new reactions have been covered and a number of new nucleophiles introduced. Some of these can lead to conjugate addition. One important new reaction is electrophilic aromatic substitution, which we met in the last chapter. Michael acceptors can combine with Lewis acids to provide electrophiles for reactions with benzene derivatives. [Pg.584]

The chemical shifts of the carbon atom bonded to the nitro group qualitatively correlate with the carbon electron density. When several nitro groups are introduced a considerably worse additivity of 13C chemical shifts compared with benzene derivatives is observed. The experimental 13C shielding in dinitroimidazoles is smaller than that calculated by the additive scheme, and this points to a less clearly displayed conjugation between the nitro group and the imidazole ring compared with the benzene ring [339],... [Pg.202]

Having documented that we are perplexed by the differences we found for the enthalpies of formation of simple cyclopropyl and phenyl derivatives, it is premature and perhaps foolish to go from singly to doubly substituted species and expect any better understanding. Steric repulsion between vicinal groups on a cyclopropane may be expected, and hence the trans-isomQv of 1,2-dimethylcyclopropane is expected to be more stable than the cis. This is correct the enthalpies of formation of trans-1,2- and cis-1,2-dimethylcyclopropane (20c and 20b, X = Me) respectively, are (-30.7 0.8) and (-26.3 0.6) kJ moF for the liquids, and-3.8 and 1.7 kJmoF for the gases. The 1,1-dimethyl isomer (20a, X = Me) is more stable yet (-33.3 0.7) and (-8.2 1.2) kJ moF for the liquid and gas, respectively. What comparisons with benzene derivatives can we make With the 1,1-disubstituted cyclopropane isomer, seemingly none. With the cw-l,2-isomer, let s try the o-disubstituted benzene, o-xylene (47a, X = Me). With the trans-l,l-isomcr, let s try the -xylene isomer (47b,... [Pg.240]

Polyfluoroaryl-lithiums and, to a lesser extent, the Grignard reagents will decompose by a (3-elimination of metal fluoride, leaving an aryne whose properties are considerably affected by the remaining fluorine atoms. The highly electrophilic nature of these species leads to some reactions, e.g. with benzene derivatives, that are not shown by benzyne itself [228] (Figure 9.88). [Pg.346]

Different Rates and Position of Substitution with Benzene Derivatives. 128... [Pg.103]

The rates of the reaction of the OH radical with benzene derivatives are generally studied from the build-up of the transient species (OH adducts) at the absorption maxima under pseudounimolecular reaction conditions at concentrations < 10" mol dm" and the second-order rate constants were evaluated from the plots of versus [solute]. The OH radical is reactive towards arenes with diffusion-controlled... [Pg.391]

The trimerization reaction with benzene derivatives could sometimes follow a similar path but, since it also occurs with disubstituted acetylenes such as HOCH2C = CCH2OH, some other mechanism must also be operating. Schrauzer explained the cyclization of tolane with a catalyst based on bisacrylonitrilenickel and triphenylphosphine by the so-called V-complex, multicenter processes. With this process, three alkyne molecules would successively coordinate with nickel and then the ring closure would take place (See Figure 6). [Pg.342]

Lahandeira, J.J. (2001) Combination of 2D-, 3D-connectivity and quantum chemical descriptors in QSPR. Complexation of a- and p-cyclodextrin with benzene derivatives./. Chem. Inf. Comput. Sci., 41, 1561-1568. [Pg.1034]

The photochemistry of p-diketones is dramatically altered if they are converted to their boron difluoride complexes (58). The reduction potential of the complex is lowered from that of the diketone or its enol so that their excited states can act as electron transfer sensitisers of alkene photochemistry or will form exciplexes with benzene derivatives, leading to the formation of products which are apparently produced by ortho addition to the arene... [Pg.200]

Bruusgaard A. 1963. Suicide attempts with benzene derivatives. Dan Med Bull 10 142-144. [Pg.76]

Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...