Benzene M

The two substituted carbons are connected by a double bond in one structure but by a single bond in the other Because no such cases of isomerism m benzene derivatives were known and none could be found Kekule suggested that two isomeric structures could exist but mterconverted too rapidly to be separated... 

Twentieth century theories of bonding m benzene gave us a clearer picture of aromatic ity We 11 start with a resonance description of benzene... 

Because the carbons that are singly bonded m one resonance form are doubly bonded m the other the resonance description is consistent with the observed carbon-carbon bond distances m benzene These distances not only are all identical but also are intermediate between typical single bond and double bond lengths... 

An important property of aromatic hydrocarbons is that they are much more stable and less reactive than other unsaturated compounds Ben zene for example does not react with many of the reagents that react rapidly with alkenes When reaction does take place substitution rather than addition is observed The Kekule formulas for benzene seem mcon sistent with its low reactivity and with the fact that all of the C—C bonds m benzene are the same length (140 pm)... 

A methyl group is an electron releasing substituent and activates all of the ring carbons of toluene toward electrophilic attack The ortho and para positions are activated more than the meta positions The relative rates of attack at the various positions m toluene compared with a single position m benzene are as follows (for nitration at 25°C)... 

Because the carbon atom attached to the ring is positively polarized a carbonyl group behaves m much the same way as a trifluoromethyl group and destabilizes all the cyclo hexadienyl cation intermediates m electrophilic aromatic substitution reactions Attack at any nng position m benzaldehyde is slower than attack m benzene The intermediates for ortho and para substitution are particularly unstable because each has a resonance structure m which there is a positive charge on the carbon that bears the electron withdrawing substituent The intermediate for meta substitution avoids this unfavorable juxtaposition of positive charges is not as unstable and gives rise to most of the product... 

The metal-ion complexmg properties of crown ethers are clearly evident m their effects on the solubility and reactivity of ionic compounds m nonpolar media Potassium fluoride (KF) is ionic and practically insoluble m benzene alone but dissolves m it when 18 crown 6 is present This happens because of the electron distribution of 18 crown 6 as shown m Figure 16 2a The electrostatic potential surface consists of essentially two regions an electron rich interior associated with the oxygens and a hydrocarbon like exterior associated with the CH2 groups When KF is added to a solution of 18 crown 6 m benzene potassium ion (K ) interacts with the oxygens of the crown ether to form a Lewis acid Lewis base complex As can be seen m the space filling model of this... 

In media such as water and alcohols fluoride ion is strongly solvated by hydro gen bonding and is neither very basic nor very nucleophilic On the other hand the poorly solvated or naked fluoride 10ns that are present when potassium fluoride dis solves m benzene m the presence of a crown ether are better able to express their anionic reactivity Thus alkyl halides react with potassium fluoride m benzene containing 18 crown 6 thereby providing a method for the preparation of otherwise difficultly acces sible alkyl fluorides... 

Metanil yellow, diphenylaminoazo-m-benzene sulfonic acid (indicator) dissolve 0.25 g in 100 mL alcohol pH range red 1.2-2.3 yellow. 

Bcazal kem m. benzene nucleus. >kohlen wasserstofife, m.ji. betuene hydrocarbons. lack, m, benzol varnish, -faate, /. faouaae... 

Figure 8. Relations between benzene solubility and total (pyridine) solubility 273 g ZnCl2, 50 g coal Wash (M)> benzene ( 7), HzO (%), HCl...

Figure 18.16. Solid State. C-NMR spectrum of PNT-N prepared by solution polymenzation m benzene.

This addition proceeds more readily with the more electron rich 2.6-di-tert-butyl-4-methyl-X -phosphorin 109 b or 2,6-dimethyM-phenyl-X -phosphorin 109 c. The H-NMR signals are in accord with the proposed structure (Table 15). The resonance of the phospha-barrelene 110 a m benzene appears at 6 = + 65 ppm (H3PO4 standard) which corresponds to the resonance of tertiary phosphines. 

The quantity of aromatic contaminants that adsorb onto TiO2 surfaces is also relatively low. d Hennezel and Ollis [47] measured the dark adsorption of the BTEX compounds at a gas-phase concentration of 50 mg/m . Benzene displays the lowest dark adsorption, followed by ethylbenzene. Higher dark adsorption was observed for toluene and xylenes. At 50 mg/m, the dark adsorption of m-xylene was nearly 10 times that of benzene (Table 1). 

H2C CH.CcH4.CH CH,2 mw 130.18 exists as o-,m- and p-isomers. The commercial form contains the 3 isomers together with ethylvinylbenzene and diethylbenzene bivinyi-m-benzene, wh liq, easily polymerized sp gr 0.9289 at 20° fr p minus 66.9°, bp 199.5°. It can be prepd (with other products) by heating 1,3 dtethylbenzene or 3 ethyl-l-vinylbenzene superheated steam passed over a bed of activated charcoal at 700°... 

Thiophenol was percolated through iron-free silica gel. The total iron content of the thiophenol thus obtained was about 0.5 p.p.m. Benzene (AnalaR grade) was distilled over sodium and percolated through iron-free silica gel. The total iron content of benzene thus obtained was about 0.14 p.p.m. Isooctane was redistilled and similarly treated. Curves A,A and B,B of Figure 1 were duplicate runs on two separate batches of Components prepared by this procedure. 

Calculated from the data reported by D. Hardin and S. Sikorsky (46) for a compound having [Mfjf + 11.99 (neat) m) Benzene insoluble, decalin soluble fraction n) Ethyl acetate soluble fraction p) For the optical purity of the models see Tables 9 and 15 q) Referred to one monomeric unit r) In xylene solution. 

Methyl mercaptan (1) Ethyl mercaptan (s) Dimethyl disulfide (m) Benzene (m)... 

Fig. 4. Enthalpies of interaction of TMEDA as a (unction of R([TMEDA]/[Li]) for 0.02 M benzene solutions of poly(styryl)lithium...

The ortho photocycloaddition of 2,3-dihydropyran is a very efficient process [11,12]. The quantum yield, measured with a solution of 1.1 M benzene and 3.5 M 2,3-dihydropyran, is 0.7 in iso-octane and 0.78 in acetonitrile. The higher quantum yield in the more polar solvent supports the proposal that ortho photocycloaddition of alkenes to benzene involves a polar intermediate. It is useful to compare these quantum yields of product formation with the quantum yield of in-... 

Scheme 42 Photocycloaddition of benzene to 1,3-dioxole. The quantum yields [13,122] were measured at 254 nm in dioxane at 20°C with 1.1 M benzene and a dioxole concentration at which the quantum yield reached the maximum value.

Fig. 9.11 (a) Cyclic voltammogram of 0.2 M benzene in [HMIMJFAP on platinum. The numbers refer to the respective cycle. Scan rate lOmVs-. (b) SEM micrograph of the electropolymerized film on the platinum electrode after synthesis in [HMIMJFAP. 

Bis 4-ethoxyphenyltelluro]pentane3(Sodium Borohydride Reduction) A solution of 4.97 g (10 mmol) of bis[4-ethoxyphenyl] ditellurium in a mixture of 10 m/ benzene and 20 ml ethanol is refluxed under an atmosphere of nitrogen. A solution of 0.6 g (16 mmol) sodium borohydride in 1 molar aqueous sodium hydroxide is dropped into the refluxing solution of the ditellurium. Then 2.3 g (10 mmol) of 1,5-dibromopentane are added and the mixture is stirred and refluxed for 2 h. The mixture is poured into distilled water. The organic layer is separated, washed with water, and mixed with acetonitrile to induce crystallization. The crystals are separated, dried under reduced pressure over phosphorus pentoxide, and then recrystallized twice from acetonitrile the orange-yellow crystals (yield 52%) melted at 63-65°. 

Dimethyl-2-oxo-l-butyl 4-Methoxyphenyl Tellurium Dichloride1 A suspension of 1.02 g (3.0 mmol) of 4-methoxyphenyl tellurium trichloride in 10 m/ benzene is mixed with 0.516 g (3.0 mmol) 3,3-dimethyl-2-trimethylsiloxybut-1 -ene. The mixture is refluxed for 10 h, then treated with 100 ml methanol/water (1 1), and extracted with chloroform. The organic phase is separated, dried with anhydrous magnesium sulfate, filtered, and the filtrate evaporated. The residue is chromatographed on silica gel with chloroform as the mobile phase. The product is recrystallized from chloroform/petroleum ether (30-60°) yield 80% m.p. 90-92°. 

Resorcinol Benzene + H2S04 - m.benzene disulfonic acid + NaOH... 

The catalytic action of trimethylamine [84] is necessary in order to perform the acylation reaction successfully. A 200-jul volume of a 10-2 M benzene solution of the amine containing an internal standard (p-dibromobenzene or 1 -bromonaphthalene) is mixed with 200 (xl of 0.3 M trimethylamine in benzene and 25 fi of anhydride. After 15 min at... 

Foreman et al. [631] compared the direct method of the chelate formation with the preliminary ashing method for the analysis of beryllium in rat urine. A detailed study showed that both of the methods are satisfactory, whereas testing of column material and packings showed the best results for a PTFE column packed with SE-52. Down to 1 ng/ml of the element could be detected in urine with the use of an ECD and EDTA as a masking reagent and a 0.05 M benzene solution of trifluoroacetylacetone. 

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