Ketones ultraviolet spectrum

In some cases spectroscopic evidence for such species exists. Thus the ultraviolet spectrum of acetophenone in aqueous sulfuric acid changes markedly as the concentration of acid is increased.278 In concentrated sulfuric acid simple aldehydes and ketones exists completely in the conjugate acid form. Unsaturated ketones give colored solutions in sulfuric acid and have -factors greater than two. The higher i-factors... 

The liquid phase photolysis of several alcohols was first systematically studied in the years between 1910 and 1913 by Berthelot and Gaudechon using a medium pressure mercury arc (21). They recognized that the main photolysis products of primary and secondary alcohols were H2 and an equivalent amount of aldehyde and ketone, respectively (21a,b). They also found (21d) that the part of the ultraviolet spectrum active on alcohols must lie below 250 nm, while carbonyl compounds are readily decomposed by light around 250 nm and above, yielding much CO. It was concluded (21d,22) that CO was a secondary product of the alcohol photolyses and due to the photolysis of the primarily produced carbonyl compound. In aqueous solutions of the alcohols the rate of decomposition was lower (21d) but led to the same products as those found in the neat photolyses. Similar to the liquid phase results Bates and Taylor (1927) found H2 as the major product in the methanol and ethanol gas phase photolysis (23). 

After isolation as sedoheptulosan, the free sugar can be recovered through its acetate. Acetolysis of sirupy sedoheptulosan tetraacetate, in the presence of a catalytic proportion of perchloric acid, gives a crystalline sedoheptulose hexaacetate which, since its ultraviolet spectrum shows no ketonic absorption, was designated hexa-O-acetyl-a-n-alfro-heptulopyra-nose. Cautious deacetylation of this product gave sirupy sedoheptulose,... 

Let us now look at an ultraviolet spectrum, shown in Figure 4.1. The spectrum is that of a saturated ketone, butan-2-one, CH3COCH2CH3. The spectrum shows a single absorption peak at Amax 279 nm, max 16.6. This very low value of max shows us that this is a forbidden transition, an n jr transition, characteristic of an aldehyde or ketone group or a nitro group. These peaks all occur within the general range of 275-290 nm. Note that... 

Like the carbonyl groups of simple aldehydes and ketones, the carboxyl group shows only weak absorption in the ultraviolet spectrum unless it is conjugated with a carbon-carbon double bond or an aromatic ring. 

TMB (42) was first generated by Roth el al. by photochemical decarbonyla-tion of the ketone 44 in a low-temperature matrix. This preparation was intensely colored, with a main transition at 490 nm and several subsidiary absorptions. Earlier ti-CI quantum chemical computations had predicted ultraviolet-visible (UV-vis) is transitions for the singlet and triplet states of TMB, and the bands observed by the Roth group were in better agreement with the predictions for the triplet. The preparation also showed a narrow ESR spectrum interpreted by the authors as that of a triplet species with D = 0.0042 cm and E = 0.0009 cm, which gave a linear Curie plot. The authors assumed that the carriers of the UV-vis and ESR spectra were the same species, namely, triplet TMB. They concluded that TMB is a ground-state triplet, contrary to the disjoint theory and to the computational results described above. 

Similar sorts of results may be found with the nitrate anion. In this case, the nitrate ion itself has a characteristic absorption in the ultraviolet. When paired with a transition-element cation, in alcoholic solution, this absorption is markedly altered (2). It also shows alterations with other cations. In certain ketone and ether solutions, it has been possible to demonstrate further that the vibrational spectrum of the nitrate ion has been altered in such a pattern as to be consistent with a binding of one of the nitrate oxygens to the cation (2), so that major vibration now occurs between this oxygen and the rest of the bound nitrate group. 

It may be of interest to compare the photochemistry of the unsubstituted cyclic ketones. The effect of ring size on the ultraviolet absorption spectrum has been discussed (4,22) although its pertinence to the photochemistry is not obvious. 

Ultraviolet transmission spectra of irradiated films showed absorbance changes similar in sensitivity to those of yc. The spectrum itself only showed a general absorbance increase in the 220-400 m/x region, with a slight indication of band formation near 315 m/x. Plots of absorbance increases against exposure time were linear for 285 m/x (ketonic carbonyl formation) and 315 m/x, with the absorbance increase amounting to 0.32 and 0.25, respectively, for 20/x films exposed 300 min. 

Acid hydrolysis of 5-amino-5-deoxy-l,2-0-isopropylidene-o -D-xy-lofuranose (15) might be expected to afiFord 5-amino-5-deoxy-D-xylose, but instead, at 70 , 3-pyridinol (21) is the main product. If the acid hydrolysis of compound 15 is conducted at room temperature, there is obtained, besides 3-pyridinol (21), the crystalline hydrochloride of l-amino-l,5-anhydro-l-deoxy-D-fhreo-pentulose hydrate (22). The crystalline hydrate exhibits no carbonyl band in its infrared and ultraviolet spectra. The water content cannot be removed without decomposition of the compound, and is, therefore, water of constitution. The nuclear magnetic resonance spectrum of 22 lacks the signal characteristic of an anomeric proton. The free ketone group is, however, detectable by the preparation of a (2,4-dinitrophenyl)-hydrazone. 

Thioxanthiones (TX) absorb strongly in the near-ultraviolet region of the spectrum, and their reaction with amines comprises a bimolecular initiator system competitive with photodissociative initiators [138 150. The photochemistry and photophysics of TX in the presence of amines are similar to that observed for other aromatic ketones, and can be summarized by the scheme proposed by Davidson [148] (Scheme 17). 

A solvent for ultraviolet/visible spectroscopy must be transparent in the region of the spectrum where the solute absorbs and should dissolve a sufficient quantity of the sample to give a well-defined analyte spectrum. In addition, we must consider possible interactions of the solvent with the absorbing species. For example, polar solvents, such as water, alcohols, esters, and ketones, tend to obliterate vibration spectra and should thus be avoided to preserve spectral detail. Nonpolar solvents, such as cyclohexane, often provide spectra that more closely approach that of a gas (compare, for example, the three spectra in Figure 24-14). In addition, the polarity of the solvent often influences the position of absorption maxima. For qualitative analysis, it is therefore important to compare analyte spectra with spectra of known compounds measured in the same solvent. 

The formulation of aconitoline as an a , 3-unsaturated ketone should be capable of direct proof, since such ketones and their derivatives generally have characteristic ultraviolet absorption spectra unfortunately, the absorption spectrum of aconitoline is not on record, and such direct evidence in support of the reaction scheme outlined (51) is therefore not yet available. It is clear, however, that the oxidation according to the above scheme cannot proceed unless the hydroxyl group in the /3-position to the methoxyl is free some indirect evidence may be adduced for the reaction scheme since triacetylaconitine (53) in which this group is esterified is not attacked whilst mesaconitine (51) is. Moreover, of the two alkaloids, hypaconitine and pseudaconitine, containing one hydroxyl group less than aconitine, the latter (54) is, but hypaconitine (51) is not, oxidized by chromic acid it appears, therefore, that the hydroxyl group which hypaconitine lacks is that in the 3-position to one of the methoxyls, that specifically attacked by chromic acid. 

Oxidation may then be assumed (71) to give the keto acid, in which the ethylenic linkage is conjugated with the carbonyl group this placing of the ethylenic linkage is purely speculative and not fully corroborated by the ultraviolet absorption spectrum (which, instead of the high-intensity maximum near 2350 a. expected for an isocyclic a,/3-unsaturated ketone. 

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