UV and IR Spectroscopies

The IR spectra of aristolochic acids obtained as Nujol mulls usually show bands near 1689 cm- (5.92 t) (COOH), and 1348 cm- (7.42 ju) (NO2). Aristolactams exhibit a band near 1692 cm (5.91 jj) (lactam C=0). 

Ultraviolet (UV) data are seldom reported for new pyrrolizine derivatives. Flamini et al. 2001J(P1)3069 described the optical spectra of 5-amino-3-imino-l,2,6,7-tetracyano-3//-pyrrolizines 18, which exhibit an intense broad absorption band centered at ca. 580 nm. 

Bicyclic 5-5 Systems with One Bridgehead (Ring Junction) Nitrogen Atom No Extra Heteroatom 

No characteristic IR data were reported for pyrrolizines or dihydropyrrolizines. An almost complete set of vibrational frequencies was deduced by combining an infrared (IR) and a Raman spectrum of pyrrolizinone 2 2001J(P2)2195 . The experimental values thus obtained were used to scale the theoretical complete set of vibrational frequencies of 2. Using the same scaling constant, the authors proposed a set of calculated vibrational frequencies for dihydropyrrolizinone 3. 

Charge-transfer (CT) molecular complexes of some pyrazole donors (pyrazole, 4-methylpyrazole, 3-methylpyrazole, and 3,5-dimethylpyrazole) with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) and tetracyanoethylene (TCNE) as 7t-electron acceptors have been studied in methylene chloride at 25 °C by UV spectroscopy 2002SAA1895 . CT complexes of some pyrazoles with iodine as a cr-electron acceptor and with DDQ, TCNE, and chloranil (CHL) as 7t-electron acceptors were also investigated spectroscopically 2003SPL357 . In both reports, the spectral characteristics and stability constants of the CT complexes formed were discussed in terms of the nature of donor and acceptor molecular structure, as well as in relation to solvent polarity. The thermodynamic parameters (A/7, AG, and AS) associated with CT complex formation were also examined. 

The stability of the two pyrazole tautomers monosubstituted at a C-3(5) position by various substituents was investigated by theoretical IR spectroscopy and at the MP2/6-311-I— -G level 2004JMT(673)17 . For each substituent studied, the energy difference between the two tautomers, expressed in terms of AE and AG, was calculated. The F and OH substituents significantly stabilized the N(2)-H tautomer, whereas CFO, COOH, and BH2 favored the N(l)-H tautomer. 

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An azo coupling reaction of monatomic phenols with diazotized 4-nitroaniline has been investigated. By HPLC, NMR, elemental analysis, UV and IR spectroscopy it has been shown that the azo derivatives of o-guaiacol, o- and m-cresols interact with an excess of diazonium in pH interval of 4,5-9,5 and form corresponding 4,4-di(4-nitrophenylazo)-2,5-cyclohexadien-1 -ones. 

The structure of the intermediate obtained from 3-phenyl-5-amino-l,2,4-thiadi-azole (Goerdeler and Deselaers, 1958) was elucidated by UV- and IR-spectroscopy. The results are consistent with the nitrosoamine structure 3.18. Its UV spectrum (Fig. 3.4) is very similar to that of the A-methyl-TV-nitroso compound 3.19, but different from that of the isomeric compound 3.20 with a methyl group in the 4-position (Goerdeler and Deselaers, 1958). The spectrum of this 4-methyl derivative is expected to be similar to that of the nitrosoamine structure 3.21, which is obviously not present, at least not in detectable tautomeric equilibrium concentration. 

A matrix isolation IR study of cyclic siladienes was more successful (Khabashesku et al., 1992). At first, unstable l-silacyclopenta-2,4-diene [128] was generated by vacuum pyrolysis (800°C 10 -10 Torr) of 5-silaspiro[4.4]nona-2,7-diene [129] or pyrolysis and photolysis (A = 248 nm) of l,l-diazido-l-silacyclopenta-2,4-diene [130] it has been studied by UV and IR spectroscopy in an argon matrix at 12 K. The UV band at Amax = 278 nm and nine IR bands (including two sp Si-H stretching vibrations at 2175 and 2144 cm ) have been recorded in matrix spectra of [128]. Reversible photochemical interconversion of [128] with silacy-... 

Various additives show considerable extraction resistance, such as impact modifiers (polyacrylates and polyblends PVC/EVA, PVC/ABS, etc.), highpolymeric processing aids (PMMA-based), elastomers as high-MW plasticisers, reactive flame retardants (e.g. tetrabromobisphenol-A, tetrabromophthalic anhydride, tetrabromophthalate diol, dibromostyrene). Direct measurement of additives by UV and IR spectroscopy of moulded films is particularly useful in analysing for additives that are difficult to extract, although in such cases the calibration of standards may present a problem and interferences from other additives are possible. 

The mechanism of this reaction was studied in detail, using high-pressure UV and IR spectroscopy. The first step is a fast thermal reaction of cobalt acetate with syn-gas and phosphine to from the ionic complex 7. The yellow cation is the photoactive species. 

If one compares the solvolyses of 2-bromo-l,l-diphenyl-4-(p-methoxyphenyl)-but-l-en-3-yne (57) and 4.4-diphenyl-1 -bromo-1 -(/ -mcthoxyphcny l)-buta-1,2,3-tricncs (58, X = Br) in aqueous ethanol (equation 21), the destabilization of the intermediate cation 59 by the large inductive effect of the triple bond as compared to its conjugative effect is evident42. Only in the case of 58 could the substitution product butatrienyl enol ether 60 be isolated in 40% yield, while it was only detected by UV and IR spectroscopy in the solvolysis product of 57. The faster observed reaction rate of 58 as compared to 57 was ascribed to a difference in their ground-state energies42. 

I. UV and IR Spectroscopy of Nitronates Table 3.9 contains selected data from UV and IR spectroscopy of different types of nitronates. It is quite evident that characteristic spectral parameters are virtually independent of the nature of the fragment bound to the oxygen atom of the nitro group. 

The basic principles of absorption spectroscopy are summarised below. These are most obviously applicable to UV and IR spectroscopy and are simply extended to cover NMR spectroscopy. Mass Spectrometry is somewhat different and is not a type of absorption spectroscopy. 

Basic instrumentation for both UV and IR spectroscopy consists of an energy source, a sample cell, a dispersing device (prism or grating) and a detector, arranged as schematically shown in Figure 2.1. 

Kinetic study of the reaction of cyclopentyl-MgBr + 4-methylmercaptoacetophenone by using stopped-flow UV and IR spectroscopies also showed that the rate constant was in the range of 2-6 s in diethyl ether at 25 °C, and the rate was first order in RMgX at low concentration (ca 0.1 M) and 0th order at high concentrations (0.3-0.8 M). The results were interpreted by the mechanism which involved pre-equilibrium of complex formation and conversion of the complex to the product. 

NMR, UV and IR spectroscopies are routinely used for the characterization of the majority of reviewed systems and the reader is referred to the individual references for this information. The special cases of structure elucidation of a secondary metabolite of the Chinese drug Danshen Salvia miltiorrhiza Bunge) by... 

Ozone can be measured by UV and IR spectroscopy. It forms an intense band at 290nm. 

Under UV-laser irradiation, photosensitive multifunctional acrylate resins become rapidly cross-linked and completely insoluble. The extent of the reaction was followed continuously by both UV and IR spectroscopy in order to evaluate the rate and quantum yield of the laser-induced polymerization of these photoresist systems. Two basic types of lasers emitting in the UV range were employed, either a continuous wave (C.W.) argon-ion laser, or a pulsed nitrogen laser. 

Anthracene consumption was followed by UV and IR spectroscopy (e379 nm = 8900 L. mof cm 1). FTIR was used also to follow the formation of hydroperoxides and to detect grafting. Hydroperoxides were also characterized by derivatization by NO gas... 

The use of modern physical methods (NMR, UV, and IR spectroscopy, mass spectrometry, and gas-liquid (GLC) and thin-layer (TLC) chromatography is becoming increasingly noticeable. By 19522 few systematic studies of the preparation of derivatives of benzo [6]thiophene had been undertaken, no attempt had been made to alkylate benzo[6]thiophene by means of the Friedel-Crafts reaction, and Friedel-Crafts acylation had been little studied. Halogenation of benzo[6]thiophene had only been superficially investigated and... 

Dimethyl-9-hydroxypyrido[ 1,2-a]pyrimidinium perchlorate and its metal complexes were characterized by UV and IR spectroscopy (90MI24). 

Argon matrix photolysis of tetrazolo[l,5-a]quinazoline/2-azidoquinazoline (96) gave a nitrene (97) which was observable by ESR, UV, and IR spectroscopy.81 The reactions of this nitrene were characterized and included fragmentation to radical species (98), rearrangement to cycloheptatetraene (99), and ring opening to a new nitrene (100). 

Two explanations have been advanced for such copolymerization behavior in hydrocarbon solvents. Korotkov (67) suggested that selective complexation or solvation of the lithium chain ends by butadiene causes an increase in the concentration of butadiene about the growing chain ends. In turn, this monomer dominates the early phases of the copolymerization. Consistent with this notion are the high entropies of activation for this copolymerization noted by Morton (68). The work of Oliver and co-workers (64, 65) adds further suggestive support to the concept of preferential solvation. They observed the interaction between the lithium and the double bond of the model compound 3-butenyllithium by 7Li-NMR, UV, and IR spectroscopy. Similar observations were made by Glaze et al. (52) and Halasa el al. (37). 

Questions concerning the application of UV- and IR-spectroscopy for solving the problem of thione-thiol dynamic tautomerism of benzothiazolinthione derivatives including nitrated ones have been considered in detail in [1250],... 

It was observed that the liquid crystalline substances incorporated on the polyimide films which were only 0.8 nm (2 layers) thick were successfully oriented to the transfer direction without a surface rubbing treatment of the polyimide film. This observation can be explained by orientation of the polymer molecule to the film transfer direction as observed by polarized UV and IR spectroscopy. 

Holm and Zienty have measured the quantum yield for the overall polymerization process of a, a -bis(4-acetoxy-3-methoxybenzylidene)-p-benzenediacetonitrile (AMBBA) crystals in slurries where scattered light was calibrated and the conversion determined by UV and IR spectroscopy or by the weight of isolated solid residues7-1. The quantum yield of the polymerization of AMBBA is 0.7 which was determined on the basis of the disappearance of two double bonds (1.4 if assigned on the basis of the number of double bonds disappeared). 

Previous attempts to estimate Drago parameters for solid surfaces met with limited success. Fowkes and co-workers (198-201) calculated Q and Ex values for SiOj, TiOj, and Fe Oj using a combination of UV and IR spectroscopies and a flow calorimeter. They determined heats of adsorption of pyridine, triethylamine, ethyl acetate, acetone, and polymethylmethacrylate (PMMA) in neutral hydrocarbon solutions. However, their results did not provide consistent Q/Ea parameters for the surface acid sites. It should be noted that the heats determined were for high surface coverages, and these values provide a lower bound for the actual acid strength distribution. 

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