Benzo thiophenes spectra

The IR spectrum of thieno[2,3-6]thiophene (1) was first reported by Godart in 1937 in work devoted to the UV and IR spectral analysis of thiophene, thienothiophene 1, and benzo[6]thiophene. Comparison of spectral features in the 4000-11,000 cm" region of thiophene and benzene, thieno[2,3-6]thiophene (1) and naphthalene, and benzo[6]-thiophene, benzene, and naphthalene demonstrated, in Godart s opinion, the similarity of IR spectra (in this region) of thiophene, thienothiophene 1, and benzo[6]thiophene, on the one hand, and benzene, thienothiophene 1, and naphth ene, on the other hand. The molecular absorption coefficients of benzene and thiophene, as well as of naphthalene and thienothiophene 1, were also similar. 

Thiocoumarins characteristically lose carbon monoxide from their strong molecular ion in the mass spectrum, thus forming a benzo[Z>]thiophene cation, invariably accompanied by a large metastable peak. Similar observations are recorded for selenocoumarins. ... 

The UV spectrum has been measured in hexane and cyclohexane other solvents also seem to have been used. In the 305-343 nm region, the UV spectrum strongly resembles that of benzo[c]thiophene.2 The lack of solvent dependence together with a mirror relationship to its fluorescence spectrum (in isopentane-methylcyclohexane 3 1 at 77°K) is indicative of the 7t,7r -character of the lowest singlet transition. ... 

The chemical shifts of the six protons in the rather complex H NMR spectrum of benzo[6]thiophenes have been estimated from specific deuteration experiments.83,87,89 The chemical shifts of H-5... 

When a cyclization reaction leads to mixtures of two isomeric benzo[6]thiophenes, their relative proportions are readily estimated by examination of the 1H NMR spectrum of the mixture.96 104-106 Mixtures obtained by acetylation98 and bromination 76,90 reactions and by Baeyer-Villiger oxidation of acetylbenzo[6]thiophenes107 have been similarly analyzed. The 19F NMR spectra of several polyfluoro-benzo[6]thiophenes have been examined,103,108-m and used to study the reaction of 4,5,6,7-tetrafluorobenzo[6]thiophene with nucleophiles.108 The tautomerism of 2-amino-,112-114 3-N-phenylamino-,116 and 3-hydroxybenzo[6]thiophene109,116-117 derivatives has been studied by 7H NMR spectroscopy. 

The main features of the mass spectrum of benzo[6]thiophene have been established by Porter,121 using the spectrum of 3-deutero-benzo[6]thiophene for comparison purposes. Triply charged ions have been detected in the mass spectra of benzo[6]thiophene and its 2- and 3-methyl derivatives.126... 

The mass spectra of 2-phenyl-, 3-phenyl-, and 3-methyl-2-phenyl-benzo[6]thiophene have been discussed, and tentative structural assignments of the main fragment ions have been made.121 The mass spectra of benzo[6]thiophene-l, 1-dioxide and its 2,3-dihydro derivative have been examined in detail.121> 127 The partial mass spectrum of 2,3-dihydrobenzo[6]thiophene has been recorded.124... 

Several workerslz0-128-131 have recorded the IR spectrum of benzo-[f>]thiophene, but the assignment of bands is far from complete. The CH out-of-plane bending (y-CH) frequencies of the benzene ring, which occur in the region 967-758 cm-1, have been most fully examined.128... 

The UV spectrum of benzo [6]thiophene has been obtained in solution120,130,134 155-167 and in the vapor phase,168-172 mainly for... 

The solvent perturbation technique has been used to study the absorption bands attributable to singlet-triplet transitions in benzo-[6]thiophene, using ethyl iodide as the perturbing solvent.173 Attempts to obtain information on the -electron conjugation in the 5-membered ring of benzo[6]thiophene by examination of the vibrational structure of the electronic spectrum were unsuccessful.171 UV evidence suggests that the valence shell of the sulfur atom can expand to a 10-electron structure in benzo[6]thiophene.156... 

A molecular orbital treatment of the UV spectrum of benzo[6]thio-phene has been given.68,72,74,75 The luminescence166,175 and phosphorescence176,177 spectra of benzo[6]thiophene have been recorded its singlet-triplet absorption spectrum has been measured.178... 

Attempts to correlate the position of the substituent with the UV spectrum have been largely unsuccessful, but some general comments may be made. The spectra of most monosubstituted derivatives resemble that of benzo [6]thiophene and the three distinct zones usually remain. Methyl or halo substituents cause an overall bathochromic shift relative to benzo [6]thiophene—zone B is most affected by 3-, 5-, or 6-substituents zone C by 5-substituents.134,159,162 3-Alkyl-benzo[6]thiophenes are characterized by zone-B bands of lower intensity than those of benzo [6]thiophene and its other alkyl derivatives.134 The UV spectra of 2-methylbenzo[6]thiophene and its selenium analog have been compared.182... 

The UV spectrum of 3-phenylbenzo[6]thiophene185, 186 resembles that of benzo[6]thiophene, since steric interaction between the ortho hydrogens of the phenyl group and H-4 prevents complete conjugation. Such steric effects are absent from 2-phenylbenzo[6]thio-phene, and its spectrum is widely different from that of the parent.174,186... 

There has been no systematic study of the spectra (mass, UV, IR, or NMR) of benzo[c]thiophene derivatives, although spectroscopic data have been recorded for individual compounds in the more recent literature. The spectroscopic data for benzo[c]thiophene itself have been recorded,5,6,12,15,16 the IR spectrum of l,3-diphenylbenzo[c]-thiophene has been studied in some detail,17 and the excitation and... 

The anion-radical of benzo[Z>] thiophene has transient occurrence in the exciplex which results when the heterocycle is irradiated in amine solvents, and the reactivity of the exciplex is explicable in terms of the distribution of spin population calculated for the anion-radical.The anion-radical 106 of benzo[c]thiophene has been formed by reduction of the parent heterocycle with potassium in Its ESR spectrum was measured and assigned. 

The anion-radical 128 of benzo[c]thiophene-l,3-dione was observed by ESR spectroscopy several years ago its electronic absorption spectrum has been recorded more recently. ... 

From such a study, it appears that the sulfur atom acts as a 71-donor. The spectrum of benzo [b]thiophene in a nematic solvent is consistent with a planar molecule without significant distortion in the geometry of the benzene and thiophene rings.71... 

The behavior of benzo[6]tellurophene under electron impact has been analyzed by Buu-Hoi and co-workers.89 The mass spectrum is similar to those of benzo[6]thiophene and benzoU>]selenophene. The base peak corresponds to a detellurated species, probably benzocyclobutadiene. 

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