Carbonyl compounds absorptions

T tt transitions.14 These generally occur near 290, 180, and 160 mp, respectively. With more complicated carbonyl compounds, absorption of other chromophores is frequently superimposed on these regions, but the n -n transition is usually still observable. 

Determination of the dissociation constants of acids and bases from the change of absorption spectra with pH. The spectrochemical method is particularly valuable for very weak bases, such as aromatic hydrocarbons and carbonyl compounds which require high concentrations of strong mineral acid in order to be converted into the conjugate acid to a measurable extent. 

The absorption of uv light produces radicals by cleavage of hydroperoxides and carbonyl compounds (eqs. 10—12)... 

The CO stretch in the infrared spectra of carbonyl compounds gives rise to a strong absorption around 1700 cm , and is often used as a diagnostic. 

The end group of the polymers, photoinitiated with aromatic amine with or without the presence of carbonyl compound BP, has been detected with absorption spectrophotometry and fluororescence spectrophotometry [90]. The spectra showed the presence of tertiary amino end group in the polymers initiated with secondary amine such as NMA and the presence of secondary amino end group in the polymers initiated with primary amine such as aniline. These results show that the amino radicals, formed through the deprotonation of the aminium radical in the active state of the exciplex from the primary or secondary aromatic amine molecule, are responsible for the initiation of the polymerization. 

Table 21.3 Infrared Absorptions of Some Carbonyl Compounds...

In the mass spectra of all these substances (4,5,14,15,87,92,94), the molecular ions peaks are present. The base peak at m/z 58, typical for all the seco alkaloids with the N,iV-dimethylaminoethyl chain, corresponding to the CH2=N(CH3)2+ ion is observed. The main mass fragmentation under electron impact seems to involve bond cleavage between C-l and C-9. This can be evidenced by the presence of ions of the 122 and 123 type found in spectra of all compounds except for N-methylhydrastines (98, 99), where the 123 — C02 ion is formed instead. Finally, the carbonyl group absorption... 

There are at least two different series of isomeric compounds having the formula Pt4(C0)sL4. One series, which is brown-black (L = PMe2Ph50, PPh3 50 2S1, PPh2(o-Tol)251, PPh(o-Tol)2 251 ) and has only bridging carbonyl infrared absorptions, has the structure shown in Fig. 19. The other series of compounds, which are all red,... 

Figure 8.33 Strong, sharp band at 1700 cnY1 indicating a carbonyl group. Absorption bands on the high side of 3000 cnY1 and a series of weak bands between 1700 and 2000 cnY1 indicating a benzene ring. Possibly benzaldehyde, or a similar compound.

Carbonyl compounds for instance can be trapped by absorption in a reagent solution containing 2, 4-dinitrophenylhydrazine and hydrogen chloride. Details of this method are extensively described elsewhere (8). The principle of the method is that the carbonyl compounds, in case of rendering plant emission the aldehydes, react with the 2,4-dinitrophenylhydrazine and form 2,4-dinitrophenylhydrazones (2,4-DNPH s) according to the scheme. 

The commonest modern method for determining the degree of hydration is to measure the intensity of the broad n- carbonyl absorption band at about 280 m/x, which disappears on hydration. Early measurements (Schou, 1926, 1929 Harold and Wolf, 1929, 1931) show considerable discrepancies, but the results of later workers are in reasonable agreement. The main uncertainty lies in the value to be assigned to the maximum extinction coefficient of the unhydrated carbonyl compound, which varies between 12 and 80 for different compounds. This is commonly taken as the value measured in a non-hydroxylic solvent such as hexane or cyclohexane, but this is not strictly valid, since the intensities of n-n- transitionsvary somewhat with the solvent (see e.g. Dertooz and Nasielki, 1961) moreover, since the shape of the band and the value of e are also solvent-dependent it may make some difference whether the extinction coefficients are compared at the same wavelength, at the respective maxima, or in terms of the band area. Special difficulties arise... 

If the solution contains an appreciable concentration of unhydrated carbonyl compound, the variation of carbonyl u.v. absorption with pH can be used to obtain (Bunnett et al., 1961 Hiiie et al., 1965). Similarly, in the weakly dissociated compounds X.CoH4.C(OH)2.CF3 the variation of the aromatic absorption with pH provides a means of determining Kx or (Stewart and Van der Linden, 1960). 

Empirical rules (Woodward s Rules) of good predictive value are available to estimate the positions of the absorption maxima in conjugated alkenes and conjugated carbonyl compounds. 

Solvent polarity may affect the absorption characteristics, in particular since the polarity of a molecule usually changes when an electron is moved from one orbital to another. Solvent effects of up to 20 nm may be observed with carbonyl compounds. Thus the absorption of acetone occurs at 279 nm in n-hexane, 270 nm in... 

In general, if no conjugation occurs, the UV-visible absorption of carbonyl compounds is below 215 nanometers (nm) and, for this reason, isn t very useful. However, in a few cases, a second absorption may be present. You can see some examples of the additional absorption band in Table 9-2. 

The first step, sometimes referred to as the zeroth law of photochemistry, is the absorption of light by the carbonyl compound. There are three absorption regions in the ultraviolet for the simplest carbonyl compounds owing to the ground state to singlet n-+ a, and... 

The initial excitation is of the carbonyl compound, rather than the olefin, since the reaction can be brought about by irradiation in a region where only the carbonyl compound absorbs. The simple olefins are essentially transparent at wavelengths longer than 250 m[x. The absorption maximum for the transition of simple olefins is shorter... 

The mixture of hydrazones formed from the reactions of the set of carbonyl compounds commonly found in air can then be separated using HPLC and detected using light absorption at 254 or 365 nm (e.g., see Kuntz et al., 1980 Lipari and Swarin, 1982 and Kuwata et al., 1983). 

Examination of the optical spectrum of the filtered purple solution gave a structured absorption band with maxima at 514 and 543 nm. This position is remarkably close (566 nm) to the n-n electronic transition predicted by Davis and Goddard for the parent system H2N=N. As expected for an n-n transition, the position of the absorption maximum is solvent dependent. In dichloromethane solution, A,i ax is 541 nm, in 2-propanol it is 526 nm. The blue shift of 15 nm is completely consistent with the n-n absorptions of isoelectronic carbonyl compounds. 

By its characteristic carbonyl IR absorption band the product of intramolecular termination, i. e. the cyclic B-ketoester was detected by Goode et al. (58), Glusker et al. (59), and Owens et al. (6o) as one of the products of the oligomerization of MMA with phenylmagnesium bromide or fluorenyllithium in toluene. The same compound was found by Lochman et al. (61) when using metalated methylisobutyrate as the initiator in a THF/pentane mixture at high initiator/monomer ratios. 

The absorptions of several carbonyl compound classes are summarized in Table 3.3. 

The compound PPN[Ru6N(CO)i 6] is obtained as brick red crystals. The solid is stable in air for several hours, but it should be stored in an inert atmosphere. It is unstable in solution over extended periods of time, even under an inert atmosphere, decomposing to form PPN[Ru5N(CO)14]. The crystals are soluble in THF, diethylether, dichloromethane, and acetone and, insoluble in hexane and water. The IR spectrum of a THF solution contains the following carbonyl stretching absorptions 2010(vs), 1965(wsh), 1839(w)cm-1. 

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