Cyclohexane ultraviolet spectrum

The ultraviolet spectrum of this material In cyclohexane solution exhibits absorbances at 381. 365. 356. and 344 nm with molar extinction coefficients of 91. 123. 97. and 60. respectively. In addition, shorter wave-length shoulders are observed. For a detailed discussion of the spectroscopic properties of acylsllanes. consult ref. 6. 

Figure 9-18 The ultraviolet spectrum of 2-propanone (acetone) in cyclohexane...

The ultraviolet spectrum of pyrazine in cyclohexane shows maxima at 260 nm (corresponding to a tt-tt transition) and 328 nm (corresponding to a n-7r transition) in each case with vibrational fine structure the coefficients of molecular extinction are 5600 and 1040, respectively.78,79 Substitution of halogen has a bathochromic effect on the ultraviolet spectrum of pyrazine.80 A useful index of the ultraviolet and visible spectra of pyrazine derivatives is available for the period from 1955 to 1963.81 The far-ultraviolet spectrum of pyrazine... 

The spectra of pyrazine, pyrimidine, and pyridazine, all in cyclohexane, are compared by Albert (1462). They show two bands with associated fine structure, the peaks for pyrazine center around 260 and 328 nm. The near-ultraviolet spectrum of pyrazine has been measured in several solvents [and at various pH values (1463)] and the transitions assigned (1474, 1482). The diffuse system at 260 nm has been attributed to rr->-7r transitions whereas the sharp system at 328 nm has been ascribed to n rr transitions (1467, 1474). Semiempirical calculations have been made on the electronic structure of pyrazine with reference to its -> rr transition (1483-1486), calculations have been made of transition energies in N-... 

The ultraviolet spectrum of the polymer, measured in cyclohexane solution, was essentially the same in the presence or absence of iodine. The polymer showed only weak absorption in CH2C]a solution, having a maximum of 258 nm (e=340/monomer unit or 27,000/polymer molecule). After treatment with a dilute solution of chlorine in CCli, the polymer no longer showed an absorption maxima at 258 nm instead, tail absorption of an intense band whose maximum would occur below 210 nm was observed. 

FIGURE 7.4 Ultraviolet spectrum of benzoic acid in cyclohexane. (From Friedel, R. A., and M. Orchin, Ultraviolet Spectra of Aromatic Compounds, John Wiley and Sons, New York, 1951. Reprinted by permission.)... 

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. 

The ultraviolet spectra of the several epiuulfides studied3 in both solution and in the gas phase are characterized by one band in the region of 2600 A (38,460 om. 1). Studies have been made on ethylene sulfide, propylene sulfide, and cyclohexane sulfide. The /solution spectra have inflections in the region of 2450 A (40,820 cm.-1). The gaa-phase spectrum reveals a distinct second transition... 

Figure 22-3 Ultraviolet absorption spectrum of benzene (in cyclohexane) showing the benzenoid" band...

The longest wavelength band in the ultraviolet (UV) spectrum of the 1 -phenyl-fV-methyl derivative of 9 was reported to occur at 356 nm in cyclohexane and displayed only slight solvatochromism, while the fluorescence spectrum ( = 0.13, cyclohexane) showed marked solvatochromism, for example, 87 nm with a change from cyclohexane to dimethylforma-mide (DMF) <1995CC1249>. No infrared (IR) data have been reported recently for borepins or their analogues. 

A solvent for ultraviolet/visible spectroscopy must be transparent in the region of the spectrum where the solute absorbs and should dissolve a sufficient quantity of the sample to give a well-defined analyte spectrum. In addition, we must consider possible interactions of the solvent with the absorbing species. For example, polar solvents, such as water, alcohols, esters, and ketones, tend to obliterate vibration spectra and should thus be avoided to preserve spectral detail. Nonpolar solvents, such as cyclohexane, often provide spectra that more closely approach that of a gas (compare, for example, the three spectra in Figure 24-14). In addition, the polarity of the solvent often influences the position of absorption maxima. For qualitative analysis, it is therefore important to compare analyte spectra with spectra of known compounds measured in the same solvent. 

The ultraviolet absorption spectrum of quinoxaline in cyclohexane shows bands with vibrational fine structure at 340 (log e 2.84), 312 (log e 3.81), and 232 nm (log e 4.51) which are attributed to n—tt and 77-77 transitions. In ethanol the vibrational fine structure disappears and the less intense n-77 band appears as a shoulder on the long-wave 77- 77 band. However in methanol and in water the n—tt band is obscured by the more intense 77-77 band. The weak n-77 bands in the ultraviolet spectra of 6-chloro- and 6-bromoquinoxaline ° and certain... 

Ultraviolet absorption data in either ethanol or cyclohexane have been tabulated for ten derivatives of the ring system. In ethanol, s-triazolo[4,3-a]pyrazine has three main bands, at 206, 253, and 292 nm, and the spectrum is very similar to that of s-triazolo[4,3-a]pyrimidine and the corresponding fused pyridine. Replacement of CH by N in the pyridine ring of s-triazolo[4,3-a]pyridine results in only small shifts in the... 

Figure 5.1 Typical UV absorption spectra for several organic molecules In solution, (a) The spectrum is that of pyridine dissolved in 95% ethanol. The absorption wavelength Is plotted on the x-axis and the logarithm of the molar absorptivity is plotted on the y-axis. (Reprinted with the pennission of the late Professor Milton Orchin. Jaffe, H.H. and Orchin, M., Theory and Applications of Ultraviolet Spectroscopy, John Wiley Sons, New York, 1962.) (b) A UV spectrum of naphthacene dissolved in cyclohexane.

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