Benzene infrared

Polyethylene is one of the very few crystalline plastics that will float on water. The specific gravity ranges from 0.91 to 0.96. It burns quickly with a blue flame with a yellow tip. Polyethylene drips while it burns and gives off a paraffin odor similar to a burning candle. Polyethylene is impervious to most common solvents. However, it can be dissolved in hot toluene or hot benzene. Infrared spectroscopy is used to confirm the identity of polyethylene. 

Using the information provided above, whieh of the C-H vibrational modes of benzene will be infrared-aetive, and how will the transitions be polarized How many C-H vibrations will you observe in the infrared speetrum of benzene ... 

Katritzky and Topsom have reviewed the information available, largely from infrared and n.m.r. studies, concerning the distortion of the tt-electron system in the benzene ring brought about in the ground state by substituents. Of particular interest is the observation that both n.m.r. studies (of m- F and chemical shifts) and infrared investigations (of the intensities of bands due to certain skeletal vibrations) suggest that the value of Taft s [Pg.226]

As discussed earlier in Section lOC.l, ultraviolet, visible and infrared absorption bands result from the absorption of electromagnetic radiation by specific valence electrons or bonds. The energy at which the absorption occurs, as well as the intensity of the absorption, is determined by the chemical environment of the absorbing moiety. Eor example, benzene has several ultraviolet absorption bands due to 7t —> 71 transitions. The position and intensity of two of these bands, 203.5 nm (8 = 7400) and 254 nm (8 = 204), are very sensitive to substitution. Eor benzoic acid, in which a carboxylic acid group replaces one of the aromatic hydrogens, the... 

Analysis. The infrared (ii), ultraviolet M, and nuclear magnetic resonance (nmr) spectra are distinct and characteristic for benzene and are widely used in analysis (78—80). Benzene also produces diagnostic ions in the mass spectmm (81,82) (see Analytical methods). 

Estrone methyl ether (100 g, 0.35 mole) is mixed with 100 ml of absolute ethanol, 100 ml of benzene and 200 ml of triethyl orthoformate. Concentrated sulfuric acid (1.55 ml) is added and the mixture is stirred at room temperature for 2 hr. The mixture is then made alkaline by the addition of excess tetra-methylguanidine (ca. 4 ml) and the organic solvents are removed. The residue is dissolved in heptane and the solution is filtered through Celite to prevent emulsions in the following extraction. The solution is then washed threetimes with 500 ml of 10 % sodium hydroxide solution in methanol to remove excess triethyl orthoformate, which would interfere with the Birch reduction solvent system. The heptane solution is dried over sodium sulfate and the solvent is removed. The residue is satisfactory for the Birch reduction step. Infrared analysis shows that the material contains 1.3-1.5% of estrone methyl ether. The pure ketal may be obtained by crystallization from anhydrous ethanol, mp 99-100°. Acidification of the methanolic sodium hydroxide washes affords 10-12 g of recovered estrone methyl ether. 

Further development of the column with 25% ethyl acetate in benzene produces 2.5 g of material, which on repeated crystallization yields 0.22 g of 17a,21-dihydroxypregn-4-ene-3,ll,20-trione 21-acetate mp 248-251°. Identity with cortisone acetate is established by a comparison of infrared spectra. Elution of the column with 30 % ethyl acetate in benzene gives after crystallization, 0.21 g of ll/9,17a,21-trihydroxypregn-4-ene-3,20-dione 21-acetate mp 219-222°. 

A mixture consisting of 0.69 g (10.5 mmoles) of zinc-copper couple, 12 ml of dry ether, and a small crystal of iodine, is stirred with a magnetic stirrer and 2.34 g (0.7 ml, 8.75 mmoles) of methylene iodide is added. The mixture is warmed with an infrared lamp to initiate the reaction which is allowed to proceed for 30 min in a water bath at 35°. A solution of 0.97 g (2.5 mmoles) of cholest-4-en-3/ -ol in 7 ml of dry ether is added over a period of 20 min, and the mixture is stirred for an additional hr at 40°. The reaction mixture is cooled with an ice bath and diluted with a saturated solution of magnesium chloride. The supernatant is decanted from the precipitate, and the precipitate is washed twice with ether. The combined ether extracts are washed with saturated sodium chloride solution and dried over anhydrous sodium sulfate. The solvent is removed under reduced pressure and the residue is chromatographed immediately on 50 g of alumina (activity III). Elution with benzene gives 0.62 g (62%) of crystalline 4/5,5/5-methylene-5 -cholestan-3/5-ol. Recrystallization from acetone gives material of mp 94-95° Hd -10°. 

A mixture of 2.0 g (0.064 mol) of 2-fluoromethyl-3-(o-tolyl)-6-nitro-4(3H)-qulnazolinone, Oi g of 5% palladium-carbon and 100 ml of acetic acid is shaken for 30 minutes in hydrogen gas. The initial pressure of hydrogen gas is adjusted to 46 lb and the mixture is heated with an infrared lamp during the reaction. After 30 minutes of this reaction, the pressure of hydrogen gas decreases to 6 lb. After the mixture is cooled, the mixture is filtered to remove the catalyst. The filtrate is evaporated to remove acetic acid, and the residue is dissolved in chloroform. The chloroform solution is washed with 5% aqueous sodium hydroxide and water, successively. Then, the solution is dried and evaporated to remove solvent. The oily residue thus obtained is dissolved in 2 ml of chloroform, and the chloroform solution is passed through a column of 200 g of silica gel. The silica gel column is eluted with ethyl acetate-benzene (1 1). Then, the eluate is evaporated to remove solvent. The crude crystal obtained is washed with isopropylether and recrystallized from isopropanol. 0.95 g of 2-fluoromethyl-3-(o-tolyl)-6-amino-4(3H)-quinazolinone Is obtained. Yield 52.5% MP 195°-196°C. 

A mixture of 20 g of 1 -bromo-3,5-dimethyladamantane, 75 ml of acetonitrile, and 150 ml of concentrated sulfuric acid was allowed to react overnight at ambient room temperature. The red reaction product mixture was poured over crushed ice, and the white solid which precipitated was taken up in benzene and the benzene solution dried over sodium hydroxide pellets. The benzene solution was filtered from the drying agent and evaporated to dryness in vacuo to yield 1 B.2 g of product having a melting point of about 97°C and identified by infrared spectrum as 1-acetamido-3,5-dimethvladamantane. 

Changes in relative peak intensity and marginal line shifts have been observed for benzene adsorbed on porous glass (26). More significantly, infrared spectroscopic evidence had been found in the appearance of inactive fundamentals for the lowering of molecular symmetry of benzene on adsorption on zeolites (47). 

The correlation analysis of infrared data has been much examined by Katritzky, Topsom and colleagues69,70. Thus, the intensities of the v16 ring-stretching bands of mono- and di-substituted benzenes may be correlated with the oR° values of the substituents and these correlations may be used to find new oR° values. 

The submitters have not been successful in isolating tert-butylcyanoketene by any method. If the solvent is removed, the ketene polymerizes. The spectral properties of the product are as follows infrared (benzene) cm.-1 2220 (C=N), 2130 (C=C=0) proton magnetic resonance (benzene) <5, multiplicity, assignment 0,75 [singlet, C(CH3)3],... 

The limitations of the reaction have not been systematically investigated, but the inherent lability of the aziridines can be expected to become troublesome in the case of epoxyketones which are slow to form hydrazones. The use of acid catalysis is curtailed by the instability of the aziridines, particularly the diphcnylaziridine, in acidic media. Because of their solvolytic lability, the hydrazones are best formed in inert solvents. A procedure proven helpful in some cases is to mix the aziridine and the epoxyketone in anhydrous benzene, and then to remove the benzene on a rotary evaporator at room temperature. Water formed in the reaction is thus removed as the azeotrope. This process is repeated, if necessary, until no carbonyl band remains in the infrared spectrum of the residue. 

Except in simple cases, it is very difficult to predict the infrared absorption spectrum of a polyatomic molecule, because each of the modes has its characteristic absorption frequency rather than just the single frequency of a diatomic molecule. However, certain groups, such as a benzene ring or a carbonyl group, have characteristic frequencies, and their presence can often be detected in a spectrum. Thus, an infrared spectrum can be used to identify the species present in a sample by looking for the characteristic absorption bands associated with various groups. An example and its analysis is shown in Fig. 3. 

Fig, 37. Far-infrared spectra of chromium, iron, and cobalt atom reactions with benzene, benzene-(f and benzene/benzene-d mixtures in argon matrices at 10-12K 171). 

Far-Infrared Bands and Shifts of the vC=C Stretching and SC-H o.p. Bending Vibrations of Benzene upon Complexation (171)... 

Otsuka et al. (107) describe [Ni(CNBu )2], as a reddish brown microcrystalline substance, which is extremely air-sensitive. It can be recrystallized from ether at —78°C, and is soluble in benzene in the latter solution the infrared spectrum (2020s, br, 1603m, 1210m) and proton NMR (three peaks of equal intensity at t8.17, 8.81, and 8.94) were obtained. Neither analytical data nor molecular weight is available on this complex. The metal-ligand stoichiometry is presumably established by virtue of the molar ratio of reactants and by the stoichiometries of various reaction products. 

The infrared region of the electromagnetic spectrum lies between the wavelengths 1000 and 15000 nm (Kemp AVellacdo, 1980). Absorption of radiation in this region by organic compounds has been known since 1866, when Tyndall first conducted experiments on the interaction of radiation with compounds such as chloroform, methyl and ethyl iodides, benzene. 

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