Benzene, absorption spectrum substituted

Quite a number of workers have examined specific aspect of the direct photolysis of substituted benzenes and, although the mechanisms are not fully understood, some important conclusions have been reached. Hentz and Burton examined the photolysis of toluene, ethyl benzene and mesitylene in both liquid and vapor states using a medium-pressure mercury lamp. They concluded that the gas-phase products, hydrogen, methane and ethane, were formed with a quantum yield of about 10 , while polymer formation was much more important. At 150 °C hydrogen was the most important gas-phase product except for the case of ethyl benzene in the vapour, where both methane and ethane were more important than hydrogen. Porter and Wright have shown by flash photolysis that benzyl radicals are formed in the photolysis of toluene and ethyl benzene and have observed the absorption spectrum of the benzyl radical. 

Absorption spectrum (cont.j silabenzene, 105, 107 substituted benzenes, 115-17 tetracene, 72, 103... 

Figure 4.43 shows the absorption spectrum of phenol. Phenol has one OH group substituted on a benzene ring, so you need to consider not only the peaks in Table 4.10 bnt also the peaks in Table 4.9 and the earlier discussion of aromatic hydrocarbons. Note that the CO H is very broad due to hydrogen bonding and the C H at abont 3050 cm , on the right side of the OH band, is a short... 

The absorption spectrum of 7 in aqueous acidic solutions has also been detected. The vertical gas-phase ionization potential /p of benzene was measured from the He(I) photoelectron spectrum as 9.23 ev.37e standard anodic peak potential Ep could not be measured directly but was estimated from data for alkyl-substituted benzenes as 2.86 V vs NHE. Jahn-Teller distortion in 7 has been reviewed, and the high-resolution state-to-state threshold photoionization spectrum of benzene gives the shape of 7 8 and diminished significantly the mystery regarding the structure. The geometries, hyperfine structure, and relative stabilities of the two mono-deuterated Jahn—Teller-distorted ions CeHsD were examined theoretically and experimentally. EPR and ENDOR studies showed the toluene radical cation possessed the B2g structure. The IR spectra of the two Jahn—Teller forms of 7 were also calculated. On the basis of the calculated energy levels, both 7 and 8 have been classified as antiaromatic. ... 

Compounds 1 and 2 were identified by FTIR and 13C-NMR. The 13C proton decoupled spectra for 1 and 2 are dominated by signals ranging from 62 to 195 ppm. The 13C chemical shift assignments were made based on comparisons with 4,4 -(hexafluoroisopropylidene)diphenol and from calculations based on substituted benzenes and naphthalenes.15 The 13C-NMR spectrum clearly showed that the Friedel-Crafts acylation of 1 by 4-fluorobenzoyl chloride yielded the 1,4-addition product exclusively. The 13C chemical shifts for 2 are listed in Table 8.1. The key structural features in the FTIR spectrum of2 include the following absorptions aromatic C-H, 3074 cnr1, ketone C=0, 1658 cm-1, aromatic ether Ar—0—Ar, 1245 cm-1, and C—F, 1175 cm-1. 

Pseudopterosin X (1) was isolated as a yellow colored gum. The UV spectrum of 1 showed maximum absorption at 280 nm due to the presence of a highly substituted benzene chromophore [10], Its IR spectmm displayed intense absorption bands at 3,470 (OH), 2,904 (CH), 1,705 (C = O), 1,595 (C = C) and 1,100 (C-0) cm . The high-resolution electron-impact mass spectmm (HREIMS) of 1 showed M+ at m/z 474.2622, and this mass provided molecular formula indicating the presence of nine double bond equivalents in 1. The C-NMR chemical shift assignments of 1 are shown around stracture 1. On the basis of the detailed NMR studies and comparison with the reported pseudopterosins in the literature and L-xylose [3-5], stmcture 1 was proposed for this new natural product. 

Chlorobenzenes absorb in the 1096-1089 cm-1 region. The position within this region depends on the substitution pattern. Aryl fluorides absorb in the 1250-1100 cm-1 region of the spectrum. A monofluo-rinated benzene ring displays a strong, narrow absorption band near 1230 cm-1. 

The absorption of aromatic compounds produces more complex spectra than that of ethylenic compounds. The 7r —> n transitions result in the presence of fine structure in the spectrum. The spectrum of benzene vapour, obtained by depositing a droplet in a quartz cell of 1 cm pathlength, is an excellent test to evaluate the resolution of instruments in the near UV (Fig. 11.1). Substitution on the benzene ring produces modifications in the shape of the absorption bands. 

Annelation on to a benzene ring increases considerably the complexity of the spectra, and indole has absorptions at 216 (4.54), 266 sh (3.76), 270 (3.77), 276 (3.76), 278 (3.76) and 287 (3.68) nm in ethanol solution. Because of the widespread occurrence of the indole ring system in nature and the sensitivity of absorption band position and intensity to substitution type, considerable use has been made of electronic spectroscopy in the past for structure identification. An extensive tabulation of data, primarily for monosubstituted derivatives, is available (71PMH(3)67,p.94). As expected, whereas the effects of alkylation are comparatively slight, introduction of groups capable of mesomeric interaction with the indole it -system may cause profound changes in the appearance of the spectrum representative examples are given in Table 24. 

Silabenzene 24 reveals a characteristic Si—H stretching vibration at 2217 cm-1, as expected for hydrogen attached to a sp2-hybridized silicon atom. Compound 24 shows a typical benzene-type UV spectrum with absorptions at X = 217, 272 and 320 nm, which fit into the series of the already known donor-substituted heterobenzenes30. An additional structural proof was the partially reversible photochemical conversion of 24 into Dewar... 

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