Spectrum benzene

Although there was no evidence in oligomers with normal BD that Li formed a localized bond at theAt carbon as illustrated in III, two experiments with 90 percent enrichment in BD- 3C2 were carried out. The )f carbon is "transparent", of course, in the samples with Cj enrichment. Figure 10 is the spectrum of the reaction product at 5°C of 1.0 M t-Bu°Li and 1.02 M BD- c in benzene. Spectrum a was taken 4 minutes after warming to reaction temperature. The peak at 137.94 ppm is the C2 carbon of the unreacted BD. In trace b, which was taken 23 minutes after warming to reaction temperature, this peak has disappeared. The trans and the cis peaks are clearly shown at 144.00 and 140.17 ppm, and are in a ratio of 3/l, respectively. The... 

Since there are normal modes of B2g and E2g symmetry, both the transitions 1 A g > 1B1 and 1A, —> 1 B2 (which are forbidden by symmetry in a rigid molecule) become allowed through vibronic coupling. These transitions account for the two weaker bands in the benzene spectrum at 2000 and 2600 A. 

Job and Littlehailes [127] have irradiated a 1 1 molar mixture of benzene and acrylonitrile under nitrogen at 0°C and obtained 7-cyanobicyclo[4.2.0] octa-2,4-diene. The reaction did not proceed in the absence of ultraviolet irradiation or in a Pyrex apparatus. The yield of photoadduct is little affected by the presence of air, which, according to the authors, strongly supports the intermediacy of a singlet excited complex. They were, however, unable to detect a UV absorption band of a ground-state complex. However, the yields of adduct were low and the possibility is considered that a low-intensity absorption band is hidden by the benzene spectrum. 

Maslen PE, Handy NC, Amos RD, Jayatilaka D. Higher analytic derivates IV anharmonic effects in the benzene spectrum. I Chem Phys 1992 97 4233-4254. 

All three major bands in the benzene spectrum correspond to tt — tt transitions. The absorption at 184 nm corresponds to the energy of the transition from one of the two HOMOs to one of the two LUMOs. The weaker band at 204 nm corresponds to a forbidden transition that would be impossible to observe if benzene were always an unperturbed, perfectly hexagonal structure. 

The benzene spectrum is one of the most studied and one of the best-known illustrations of the occurrence of line broadening in electronic tiansitions to the higher-lying excited states of a large molecule. The 2600 h4 ig) and 2000 A... 

The longest wavelength absorption in the benzene spectrum can be estimated according to this model as... 

In Figure 2.34 the spectra of some monosubstituted benzenes are shown. From these spectra it is evident that there is a continuous change from a weakly perturbed benzene spectrum to a strongly perturbed one, such as that of aniline. 

Before that time molecular orbital calculations had been made with empirical parameters found by fitting a calculated energy interval to experiment in one molecule, usually benzene, and applying it to others. In the GMS paper the required quantities were integrals over molecular orbitals calculated in a basis of Slater orbitals and without empirical quantities. As with all other calculations only the it-electrons were included, the o-electrons being supposed simply to hold the atoms in a framework. The agreement with experimental intervals in the benzene spectrum was not good, but the paper was a landmark in method. 

Fio. 3. Bathochromio shift of the benzene spectrum. Curve 1 vapor adsorbed on a silica gel disk (pressure 12.7 mm Hg) curve 2 vapor at 13.8 mm Hg (D scale x 5). Photoelectric records, from Okuda (37). 

Before obtaining an INS spectrum all relevant information on the sample should have been studied and an idea formulated as to the likely bands in the spectrum and the broad distribution of intensities. Often the best estimate of the likely spectrum will result from ab initio calculations and this partly synthetic approach will be used to inform our interpretation of the benzene spectrum. 

The first thing to note is that the overall pattern is good, we have obviously measured a benzene spectrum very similar to that calculated. We can immediately conclude that there are no strong intermolecular interactions in the crystal. 

Figure 3. ESR spectrum of PMDT Na+C10H8 ion pairs in benzene. Spectrum shows 23Na hf splitting of the 25-line pattern of the C10H8 anion. This splitting is shown for the central (0, 0) and the outermost (2,2) line of the free anion.

Figure 4. ESR spectrum of initial product of sodium reduction of Ci0H8 + TMED in benzene. Spectrum is that of an ion cluster and shows hf interaction with two equivalent 23Na cations.

Spectrum Chemical Fact Sheet Benzene. Spectrum Laboratories. http //www.speclab.com/compound/c71432.htm (accessed on September 21, 2005). 

All three major bands in the benzene spectrum correspond to transi-... 

Investigations of IR spectra of [Cr(C6H6)(CO)3] and [Cr(C6D6)(CO)3] showed that the benzene ligand has C symmetry. The bands of the benzene spectrum which lie at ca 1600 and 1500 cm become shifted to lower frequencies after the benzene molecule is coordinated to the metal. 

The physico-chemical properties of monosubstituted benzenes were discussed in terms of inductive and resonance effects [9-1 ], the last being very important in the interpretation of electronic spectra and of dipole moments. In vapour phase, the near ultraviolet spectra of monosubstituted benzenes are shifted towards longer wave lengths as compared to the benzene spectrum [15]. Sponer et al [16] have established such a shift of, 035 cm for aniline. We established the position of the electronovibrational component max vapour phase, at 39,6 0 cm for benzene, and at 3, 870 cm... 

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