Benzene, absorption spectrum

Figure 6. Comparison of benzene absorption spectrum in methanol (32 OMA accumulations) with published absorption spectrum of benzene in water...

Effect of the monochromator s slit width on noise and resolution for the ultraviolet absorption spectrum of benzene. The slit width increases from spectrum (a) to spectrum (d) with effective bandpasses of 0.25 nm, 1.0 nm, 2.0 nm, and 4.0 nm. 

In Section 17.13 reference has been made to the influence of various substituents in the benzene ring on the absorption of ultraviolet radiation, and the purpose of this exercise is to examine the effect in the case of benzoic acid by comparing the absorption spectrum of benzoic acid with those given by 4-hydroxybenzoic acid and 4-aminobenzoic acid. 

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. 

The vibronic coupling model has been applied to a number of molecular systems, and used to evaluate the behavior of wavepackets over coupled surfaces [191]. Recent examples are the radical cation of allene [192,193], and benzene [194] (for further examples see references cited therein). It has also been used to explain the lack of structure in the S2 band of the pyrazine absorption spectrum [109,173,174,195], and recently to study the photoisomerization of retinal [196],... 

Irradiation of a benzene solution of DABA at room temperature with a nitrogen laser (Horn and Schuster, 1982) gives the transient absorption spectrum shown in Fig. 3. This spectrum was recorded 50 ns after irradiation of the diazo-compound and decays over a period of ca 250 ps by a path exhibiting complex kinetic behavior. This transient spectrum is essentially identical with the low temperature optical spectrum described above, and thus is similarly assigned to 3BA. 

Fig. 3 Transient absorption spectrum recorded 50 ns after irradiation of DABA in benzene solution. The region between 370 and 440 nm is obscured by the absorption of the diazo compound...

Figure 2.6 Absorption spectrum of a solution of anthracene in benzene, and the vibronic transitions responsible for the vibrational line structure...

Figure 4.2 Absorption spectrum (continuous line) and fluorescence spectrum (dashed line) of anthracene in benzene...

Other experimental evidence leads to essentially the same conclusion regarding the n ionization of pyridine. El Sayed and Kasha (1961) have detected Rydberg series in the absorption spectrum similar to those in benzene and ascribable to n orbitals (9-266 e.v., 02 11-56 e.v., 62) and, in addition, reported a fragmentary series leading to a third ionization potential of 10-3 e.v. which they ascribed to the nitrogen lone pair. Similar values are found by photoelectron spectroscopy which also indicated the 10-3 e.v. (10-54 e.v.) level to be only weakly bonding. 

Figure 4.8 shows the UV absorption spectrum of a 100 mg/100 ml solution of ephedrine. Ephedrine has the simplest type of benzene ring chromophore, which has a spectrum similar to that of benzene with a weak symmetry forbidden band ca 260 nm with anA (1%, 1 cm) value of 12. Like benzene its most intense absorption maximum is below 200 nm. There are no polar groups attached to or involved in the chromophore so that its vibrational fine structure is preserved because the chromophore does not interact strongly with the solvent. 

The LFP of diphenyldiazomethane ( DDM ) in a variety of solvents produces triplet diphenylcarbene ( DPC, 14a), whose transient absorption is readily monitored. The optical absorption spectrum of DPC is quenched by methanol and yields the product of O—H insertion, suggesting that DPC is quenched by the O—H bond of methanol. The quenching rate constant (fex) is determined to be 6.8 X 10 M s in benzene. ... 

Benzene. The ultraviolet absorption spectrum of benzene is characterized by the low intensity L band at 256 nm and the more intense La band at about 200 nm, both bands being 77 77 transitions. Changes in the absorption spec-... 

Azulene. The absorption spectrum of azulene, a nonbenzenoid aromatic hydrocarbon with odd-membered rings, can be considered as two distinct spectra, the visible absorption due to the 1Lb band (0-0 band near 700 nm) and the ultraviolet absorption of the 1L0 band.29 This latter band is very similar to the long wavelength bands of benzene and naphthalene CLb) and shows the same 130 cm-1 blue shift when adsorbed on silica gel from cyclohexane.7 As in the case of benzene and naphthalene, this blue shift is due to the fact that the red shift, relative to the vapor spectra, is smaller (305 cm"1) for the adsorbed molecule than in cyclohexane solution (435 cm"1). Thus it would appear that the red shifts of the 1La band are solely due to dispersive forces interacting with the aromatic molecule, in agreement with Weigang s prediction,29 and dipole-dipole interaction is negligible. 

Benzidine [92-87-5] M 184.2, m 128-129 . Its soln in benzene was decolorized by percolation through two 2-cm columns of activated alumina, then concentrated until benzidine crystd on cooling. Recrystd alternatively from EtOH and benzene to constant absorption spectrum [Carlin, Nelb and Odioso JACS 73 1002 7957]. Has also been crystd from hot water (charcoal) and from ethyl ether. Dried under vac in an Abderhalden pistol. Stored in the dark in a stoppered container. CARCINOGENIC. 

A sharp decrease in the hydroxyl concentration was observed when small amounts of CO or of hydrocarbon penetrated into the discharge tube. It might be such as to prevent detection of hydroxyl by its absorption spectrum. In order to restore the hydroxyl concentration it was necessary to clean the discharge tube and the reaction vessel by means of a discharge with water vapor lasting for several hours. For instance, after having worked with benzene without controlling the presence of hydroxyl, the latter was not detected in the reaction vessel. 

Several reports have appeared in which the UV absorption spectrum of PS was found to be qualitatively similar to an alkyl benzene model compound. Vala and Rice15> demonstrated the similarity between atactic PS and ethyl benzene this was confirmed for atactic PS in cyclohexane by Hirayama 16) and in tetrahydrofuran by Abuin 17>. Bovey and co-workers20) found that absorbance spectra for isotactic PS, atactic PS, and styrene-methylmethacrylate copolymers in 1,2-dichloroethane were roughly similar to that of toluene. 

This system (see Fig. 17) is unique in many aspects of the structure and dynamics and has historic roots for nearly 50 years since the seminal works by Hildebrand and Mulliken. Mixing of benzene and iodine results in a new color, a new absorption spectrum, and a new theory. 

Probably the first isolation of a triphenylmethyl carbocation salt was by Gomberg and Cone (68) who successfully prepared the perchlorate from the corresponding chloride. A direct synthesis from the carbinol was achieved at about the same time (69), and more recently the preparation of the perchlorate and tetrafluoroborate have been much improved (70). Anderson (7/) succeeded in recording the characteristic visible absorption spectrum of the ion in concentrated acids, and Fairbrother and Wright (72) observed the same absorption when triphenylmethyl bromide was ionised in benzene in the presence of stannic bromide. 

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