Aldehydes absorption spectra

Dobbie and Tinkler suggested that, sipce hydrastinine in solution in ether or chloroform has an absorption spectrum almost identical with that of hydrohydrastinine, whilst the absorption spectra of its solutions in water or alcohol resemble those of the salts, it may exist in two forms, represented by formula I (solid state or dissolved in ether or chloroform), and II (dissolved in water or alcohol) these conclusions have been confirmed by Steiner. No evidence for the existence of Roser s aldehydic form was obtained. 

Properties of panal (Nakamura etal., 1988a). Purified panal is a colorless, amorphous solid, soluble in alcohols, water, ethyl acetate, and chloroform. The absorption spectrum (Fig. 9.3) shows a single peak (A.max 217nm, e 15,300). Optical rotation [a]D —17° (c 0.9, methanol). Mass spectrometry and NMR analysis showed that panal is a sesquiterpene aldehyde, C15H18O5 (Mr 278.30), with the structure shown below. 

The hydrolysis of the cyclic acetal, which was used as the connecting group between the polymer chain and the lipid, was confirmed both by the IR and the proton NMR spectra of the lipid recovered from the vesicular system after standing for 3 weeks at room temperature. The lactone absorption at 1805 cm-1 disappeared from the IR spectrum (Figure 6) as the result of hydrolysis. Furthermore, a new aldehyde absorption band at 1705 cm 1 was observed in the spectrum, which is related to the substituted benzaldehyde group of the hydrolyzed product. The proton NMR spectrum (Figure 10) also clearly showed the formation of the benzaldehyde, as indicated by the peak at 810.20 ppm. 

The method was first applied by Rothman, Case, and Kearns to the determination of the Ti- -So absorption spectrum of 1-bromonaphthalene. Sixteen photochemically active aromatic ketones cind aldehydes have been investigated by Kearns and Case Transitions from So to two triplet states were located and assigned as n,n ) and... 

However, as discussed in Chapter 4, the absorption spectrum of higher aldehydes cuts off at shorter wavelengths than formaldehyde. This, combined with higher quantum yields for radical production in the 290- to 340-nm range and the fact that HCHO produces 2H02 essentially immediately upon dissociation, makes the photolysis of aldehydes larger than formaldehyde less important at equal concentrations of the aldehydes. 

The spectrum of 2-phenylpropionaldehyde, illustrating typical aldehydic absorption characteristics, is shown in Figure 3.22. 

The UV-visible absorption spectrum of the monoprotonated form of PLP was divided mathematically into individual bands for the aldehyde with dipolar ionic ring (+), the aldehyde tautomer with an uncharged ring (0) and the hydrate of the dipolar ion. The following fractions were estimated (Harris et al, 1976, Biochem. Biophys. Acta. 521,181-194. 

The Pharmacopea and the Essential Oil Association of the United States require the following analyses as an index of oil purity refractive index, optical rotation, refractive index and optical rotation of a 10% distillate, specific gravity, aldehyde content, evaporation residue and ultraviolet absorption spectrum (Kesterson et al. 157 and Sale 29). 

Identification The infrared absorption spectrum of the sample exhibits relative maxima at the same wavelengths as those of a typical spectrum as shown in the section on Infrared Spectra, using the same test conditions as specified therein. Assay Not less than 80.0%, by volume, of total aldehydes. Angular Rotation Between -1° and +1°. 

Electronic Spectrum. Acetone is the simplest ketone and thus has been one of the most thoroughly studied molecules. The it n absorption spectrum extends from 350 nm and reaches a maximum near 270 nm (125,175). There is some structure observable below 295 nm, but no vibrational and rotational analysis has been possible. The fluorescence emission spectrum starts at about 380 nm and continues to longer wavelengths (149). The overlap between the absorption and the fluorescence spectra is very poor, and the 0-0 band has been estimated to be at - 330 nm (87 kcal/mol). The absorption spectra, emission spectra, and quantum yields of fluorescence of acetone and its symmetrically methylated derivatives in the gas phase havbe been summarized recently (101). The total fluorescence quantum yield from vibrationally relaxed acetone has been measured to be 2.1 x 10 j (105,106), and the measurements for other ketones and aldehydes are based on this fluorescence standard. The phosphorescence quantum yield is -0.019 at 313 nm (105). 

Recently, Kemal and Bruice (1976) have produced chemical evidence to confirm this hypothesis. They have shown that a synthetic 4a-hydroperoxy-5-ethyl-3-methyllumiflavine (F1R-OOH) has the same absorption spectrum as intermediate II. Moreover, many similarities are found to exist between the synthetic FlR-OOH and intermediate II (a) they both react with aldehydes to produce light (b) the aldehyde is converted to an acid (c) as in the case with the enzymic reaction, chemiluminescence of FlR-OOH occurs equally in anaerobic and aerobic conditions, with exponential decay. 

The solution frequently becomes warm,12 and its refractive index,1 viscosity,2 freezing point-composition curve,3 and ultraviolet absorption spectrum 36 are not those which would be expected if no reaction took place. Usually hydrates or hemiacetals of simple aldehydes are too unstable to be isolated, but a number of them are actually known and their physical properties have been determined.4 When the carbonyl group is attached to an electron-attracting group (making the carbonyl carbon atom abnormally positive), stable hydrates are frequently formed. Glyoxal, chloral, and ketomalonic acid are common examples. 

To ensure that photolysis is the only loss process for the aldehyde experiments can be carried out in the presence of an excess concentration of a radical scavenger such as cyclohexane. In cases where the high concentration of a scavenger is undesirable, e.g. because it causes saturation in the infrared absorption spectrum, a tracer compound, such as di-n butyl ether, can be used to correct for the measured decay of the aldehyde in order to obtain the j value. Typical starting concentrations used in photolysis experiments at EUPHORE are [aldehyde] = 0.5-1.5 ppmv, [scavenger] = 10-50 ppmv or [tracer] = 0.1-02. ppmv (Wenger et ai, 2004 and Magneron et al, 2002). 

The introduction of a second substituent into an aromatic ring may have a very small or a very dramatic effect on the positions of the absorption bands. If both substituents are electron donors or electron acceptors, the effect of the second substituent will usually be rather small. If the two substituents are not identical, the electron donor with the highest-energy lone pair will dominate the spectrum. For example, the absorption spectrum of m-aminophenol will be very close to that of aniline. If the two substituents are electron acceptors, the one with the stronger electron-withdrawing influence will appear to be the dominating factor. The absorption spectrum of pyridine 3-aldehyde, for example, appears in very nearly the same place as the spectrum of benzaldehyde. If, however, one substitu-... 

Identification of the Fluorescent Species. Figure 2 compares the fluorescence excitation spectra of the polymers with the absorption spectrum of a simple ,/3-unsaturated carbonyl compound (pent-3-ene-2-one) (13). The three spectra are very similar. Figure 2 shows also that the fluorescence from the polymers in the region 300-400 nm cannot be caused by the presence of polynuclear aromatic hydrocarbons such as naphthalene as postulated earlier by Carlsson and Wiles (13). Furthermore, as shown below, the excitation spectrum also differs significantly from that of a fully saturated aldehyde or ketone. 

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