Aldehydes absorption

Since the unpurified toxins show no aldehyde absorption, it was of interest to identify the precursors of helminthosporol and helminthosporal. Thin-layer chromatography of fresh chloroform extracts of the toxin that had been concentrated below 40° indicated several spots (6). One was identified as prehelminthosporol, a hemiacetal (X), from NMR spectra and chemical reactions. Refluxing with triethylamine yielded helminthosporol, identical with Tamura s prod-... 

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

Spectroscopic Properties. Characteristic aldehyde absorptions are summarized in Table 3. A carbonyl stretching frequency between 1720 and ... 

Figure 16.2. Control of the synthesis via FT-IR-spectroscopy (KBr-method). From top to bottom poly-mer-Z-Cl-resin (P-Z-resin, v (C=0) = 1774 cm 1) P-Z-fluorenyl methyl ester (v (C=0) = 1726 cm-, 5(C—C, fluorene) = 740 cm- ) P-Z-amino acid (fluorene absorption disappeared) P-Z-amino acid pen-tafluorophenylester (v (C=0) = 1794 cm "P-Z-amino alcohol (Pfp-ester absorption disappeared) P-Z-amino aldehyde (v(C—H, aldehyde) = 2720 cm-1) P-Z-imine (v(C=N) = 1670 cm-1, aldehyde absorption disappeared) P-Z-carboline (imine absorption disappeared). (Reproduced from [26].)...

Of the compounds reported to be crystalline, most are obviously not free aldehydes as they exhibit no aldehyde absorption in the infrared. The only exception, so far, seems to be methyl 2-formyl-3,4-0-isopropylidene-/3-L-pentoside. The compounds can exist as internal hemiacetals, or dimers, as shown for l,2-0-isopropylidene-a-D-a 3/lo-pentodialdo-l,4-furanose, as hemialdals (cyclization by the addition of water across two aldehyde groups) as suggested for the dialdoses from the splitting of two streptamine derivatives, or as hydrates, as proposed for D-gluco-hexodialdose. ... 

The spectroscopic properties of these isomers are in accord with their formulation as the C-17 epimeric 0,X-diacetyl derivatives XV and XVI (R = OAc). Neither epimer exhibits aldehyde absorption in the IR-spectrum or aldehydic proton signals in the NMR-spectrum. Further,... 

Table 5.7 Rules for a, -Unsaturated Ketone and Aldehyde Absorptions...

The reaction mixtures were then filtered to remove zinc oxide, washed with water to remove excess acetic acid and then dried. Removal of the solvent by distillation then yielded the aldehyde-functional polysiloxanes. Listed below are the polymers prepared for use in this study. The polymers exhibited characteristic aldehyde absorption at- 1733 cm . ... 

UV-VIS Aldehydes and ketones have two absorption bands in the ultraviolet region Both involve excitation of an electron to an antibonding tt orbital In one called a TT TT transition the electron is one of the tt electrons of the C=0 group In the other called an n ir transition it is one of the oxygen lone pair electrons Because the tt electrons are more strongly held than the lone parr electrons the transition is of... 

Acids generally absorb more strongly than esters, and esters more strongly than ketones or aldehydes. Amide absorption is usually similar in intensity to that of ketones but is subject to much greater variations. 

The amount of a particular component in a sample can be monitored by examining the height of a spectral absorption peak The reduction of an aldehyde to an alcohol would show up as a decrease in line intensity for the carbonyl and an increase for the hydroxyl peaks in the spectrum. Changes in the relative importance of different relaxation modes in a polymer can also be followed by the corresponding changes in a mechanical spectrum. 

High purity acetaldehyde is desirable for oxidation. The aldehyde is diluted with solvent to moderate oxidation and to permit safer operation. In the hquid take-off process, acetaldehyde is maintained at 30—40 wt % and when a vapor product is taken, no more than 6 wt % aldehyde is in the reactor solvent. A considerable recycle stream is returned to the oxidation reactor to increase selectivity. Recycle air, chiefly nitrogen, is added to the air introducted to the reactor at 4000—4500 times the reactor volume per hour. The customary catalyst is a mixture of three parts copper acetate to one part cobalt acetate by weight. Either salt alone is less effective than the mixture. Copper acetate may be as high as 2 wt % in the reaction solvent, but cobalt acetate ought not rise above 0.5 wt %. The reaction is carried out at 45—60°C under 100—300 kPa (15—44 psi). The reaction solvent is far above the boiling point of acetaldehyde, but the reaction is so fast that Httle escapes unoxidized. This temperature helps oxygen absorption, reduces acetaldehyde losses, and inhibits anhydride hydrolysis. 

Iron Porphyrins. Porphyrias (15—17) are aromatic cycHc compouads that coasist of four pyrrole units linked at the a-positions by methine carbons. The extended TT-systems of these compounds give rise to intense absorption bands in the uv/vis region of the spectmm. The most intense absorption, which is called the Soret band, falls neat 400 nm and has 10. The TT-system is also responsible for the notable ring current effect observed in H-nmr spectra, the preference for planar conformations, the prevalence of electrophilic substitution reactions, and the redox chemistry of these compounds. Porphyrins obtained from natural sources have a variety of peripheral substituents and substitution patterns. Two important types of synthetic porphyrins are the meso-tetraaryl porphyrins, such as 5,10,15,20-tetraphenylporphine [917-23-7] (H2(TPP)) (7) and P-octaalkylporphyrins, such as 2,3,7,8,12,13,17,18-octaethylporphine [2683-82-1] (H2(OEP)) (8). Both types can be prepared by condensation of pyrroles and aldehydes (qv). 

Examples are given of common operations such as absorption of ammonia to make fertihzers and of carbon dioxide to make soda ash. Also of recoveiy of phosphine from offgases of phosphorous plants recoveiy of HE oxidation, halogenation, and hydrogenation of various organics hydration of olefins to alcohols oxo reaction for higher aldehydes and alcohols ozonolysis of oleic acid absorption of carbon monoxide to make sodium formate alkylation of acetic acid with isobutylene to make teti-h ty acetate, absorption of olefins to make various products HCl and HBr plus higher alcohols to make alkyl hahdes and so on. 

Therefore it is possible to determine absorption spectra directly on the TLC plate by comparison with a substance-free portion of the layer. The wavelengths usually correspond to the spectra of the same substances in solution. However, adsorbents (silanols, amino and polyamide groups) and solvent traces (pH differences) can cause either bathochromic (ketones, aldehydes [60, 61], dyestuffs [62]) or hypsochromic (phenols, aniline derivatives [63]) shifts (Fig. 23). 

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. 

UV-VIS Aldehydes and ketones have two absorption bands in the ultraviolet region. 

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