Absorption carbonyl

The 4-hydroxy-THISs are extremely hygroscopic hydrolysis affords the parent thiobenzimide (3). When R" = Me and R = p-ClPh or Ph, but not p-NOjPh the nondipolar tautomer 3 (X = 0, Y = CH2) is present according to NMR and infrared spectra, the latter exhibiting carbonyl absorption at 1710 to 1720 cm ... 

Scheme 30) (6). Infrared spectra of the products possess a normal amide carbonyl absorption, indicating that the products are not present on the dipolar form (30) but rather as the neutral A -thiazoline tautomer (31 or 32) (6). 

Increased single bond character in a carbonyl group is associated with a decreased carbon—oxygen stretching frequency Among the three compounds benzaldehyde 2 4 6 trimethoxybenzaldehyde and 2 4 6 trinitrobenzaldehyde which one will have the lowest frequency carbonyl absorption" Which one will have the highest" ... 

The role of specific interactions in the plasticization of PVC has been proposed from work on specific interactions of esters in solvents (eg, hydrogenated chlorocarbons) (13), work on blends of polyesters with PVC (14—19), and work on plasticized PVC itself (20—23). Modes of iateraction between the carbonyl functionaHty of the plasticizer ester or polyester were proposed, mostly on the basis of results from Fourier transform infrared spectroscopy (ftir). Shifts in the absorption frequency of the carbonyl group of the plasticizer ester to lower wave number, indicative of a reduction in polarity (ie, some iateraction between this functionaHty and the polymer) have been reported (20—22). Work performed with dibutyl phthalate (22) suggests an optimum concentration at which such iateractions are maximized. Spectral shifts are in the range 3—8 cm . Similar shifts have also been reported in blends of PVC with polyesters (14—20), again showing a concentration dependence of the shift to lower wave number of the ester carbonyl absorption frequency. 

IR spectra of diaziridinones show carbonyl absorption at relatively high wave numbers, as found for aziridinones and cyclopropanones, absorbing at 1855-1880 cm (69JOC2254). 

The most informative feature of the IR spectra of azetidin-2-ones is generally the /3-lactam carbonyl absorption, the frequency of which is affected by substitution and by fusion of the ring (c/. Table 3). Thus, IR spectra of simple monocyclic /3-lactams generally have absorption maxima in the region 1730-1760 cm while the fused 2- and 3-cephem systems (60) and (61) show IR maxima in the regions 1772-1784 and 1782-1792 cm S respectively (b-72MI50900 p. 318). 

The higher frequencies of the /3-lactam carbonyl absorption in fused systems has been attributed to increased inhibition of amide resonance as the /3-lactam ring becomes less planar (b-72mI50900 p. 303). For the 3-cephems (61) there is also the possibility of enamine resonance which could further reduce the ability of the /3-lactam nitrogen to contribute to amide resonance. 

IR spectra of systems related to /3-lactams show the expected trends in the frequency of the carbonyl absorption, where present. For example, the presence of an exocyclic double bond at C-4 in an azetidin-2-one raises the value of vc=o considerably. Thus the 4-thioxoazetidin-2-one (62 Z=S) and the derived 4-alkylidene systems (62 Z = CR R ) exhibit /3-lactam carbonyl absorptions at 1835 and 1800-1810 cm respectively (80JOC1477, 80JOC1481), while the 4-iminoazetidin-2-ones (63) have vc=o at 1800-1825 cm (81CC41). Additional spectral data for these and similar systems may be found in the references in Table 5. 

The role of IR spectroscopy in the early penicillin structure studies has been described (B-49MI51103) and the results of more recent work have been summarized (B-72MI51101). The most noteworthy aspect of a penicillin IR spectrum is the stretching frequency of the /3-lactam carbonyl, which comes at approximately 1780 cm" This is in contrast to a linear tertiary amide which absorbs at approximately 1650 cm and a /3-lactam which is not fused to another ring (e.g. benzyldethiopenicillin), which absorbs at approximately 1740 cm (the exact absorption frequency will, of course, depend upon the specific compound and technique of spectrum determination). The /3-lactam carbonyl absorptions of penicillin sulfoxides and sulfones occur at approximately 1805 and 1810 cm respectively. The high absorption frequency of the penicillin /3-lactam carbonyl is interpreted in terms of the increased double bond character of that bond as a consequence of decreased amide resonance, as discussed in the X-ray crystallographic section. Other aspects of the penicillin IR spectrum, e.g. the side chain amide absorptions at approximately 1680 and 1510 cm and the carboxylate absorption at approximately 1610 cm are as expected. 

The purity of cyclobutanone was checked by gas chromatography on a 3.6-m. column containing 20% silicone SE 30 on chromosorb W at 65°. The infrared spectrum (neat) shows carbonyl absorption at 1779 cm. - the proton magnetic resonance spectrum (carbon tetrachloride) shows a multiplet at 8 2.00 and a triplet at S 3.05 in the ratio 1 2. 

Most other studies have indicated considerably more complex behavior. The rate data for reaction of 3-methyl-l-phenylbutanone with 5-butyllithium or n-butyllithium in cyclohexane can be fit to a mechanism involving product formation both through a complex of the ketone with alkyllithium aggregate and by reaction with dissociated alkyllithium. Evidence for the initial formation of a complex can be observed in the form of a shift in the carbonyl absorption band in the IR spectrum. Complex formation presumably involves a Lewis acid-Lewis base interaction between the carbonyl oxygen and lithium ions in the alkyllithium cluster. 

Shugar and FoxS " reported that 4-ethoxypyrimidin-2-one exists in the 0X0 form 102 since its ultraviolet spectrum is different from that of 103. They further claimed that the isomeric compound, 2-ethoxy-4-hydroxypyrimidine, existed in the hydroxy form (104) however, reexamination of the ultraviolet spectral data suggests that this unlikely conclusion may be incorrect, and the infrared spectrum of 104 does, indeed, show a carbonyl absorption band. 2-Methylthiopyrim-idin-4-one has been reported to exist in the hydroxy form, but this to appears unlikely. 

The Apomorphine-derived alkaloid PO-3 (129) was isolated as violet needles after crystallization from acetone and ether from Papaver orientale (66MI2), but was not found in the green solutions of autoxidized apomorhine hydrochloride (62M941, 68HCA683) (Scheme 51). No anion was detected by elemental analysis. The pA"a of PO-3 is 3.88 0.02 in 50% ethanol. The IR spectrum displays no carbonyl absorption between 1650 and 1700 cm (69MI2). The UV absorption maxima of PO-3 are in agreement with the formulation of a mesomeric betaine [T-max (EtOH) = 310... 

Ultraviolet and infrared spectroscopy indicate that quinoxaline-2,3-dione type structures are preferred to tlie tautomeric 3-hydroxy-quinoxalin-2 One or 2,3-dihydroxyquinoxaline forms. The light absorption properties (UV) of quinoxaline-2,3-dione have been compared with those of its NN -, ON-, and OO -dimethyl derivatives (79, 80, and 81), and also its N- and 0-monomethyl derivatives (43 and 82). The parent dicarbonyl compound and its mono- and di-A -methyl derivatives show very strong carbonyl absorption near to 1690 cm split into two peaks. 

Attempts were made to estimate the amount of the second form by studying the weak absorption band of malonaldehyde solutions at 350 mju. This band has been attributed to nonconjugated carbonyl absorption—i.e. to the dialdehydo form of malonaldehyde (40, 48). 

By monitoring the intensity of the carbonyl absorption it was observed that oxidation of methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexopyrano-side with chromium trioxide-pyridine at room temperature gave initially the hexopyranosid-3-ulose (2) in low concentration, but attempts to increase this yield resulted in elimination of methanol to give compound 3. However, when methyl 4,6-0-benzylidene-2-deoxy-a-D-Zt/ ro-hexo-pyranoside is oxidized by ruthenium tetroxide in either carbon tetrachloride or methylene dichloride it affords compound 2 without concomitant elimination. When compound 2 was heated for 30 minutes in pyridine which was 0.1 M in either perchloric acid or hydrochloric acid it afforded compound 3, but in pyridine alone it was recoverable unchanged (2). Another example of this type of elimination, leading to the introduction of unsaturation into a glycopyranoid ring, was observed... 

Tests. Chem analysis consists of reaction with KI soln and titration of the liberated I with Na thiosulfate soln. Instrumental analysis consists of measurement of the carbonyl absorption at 1760cm 1 using an infrared spectrophotometer. This procedure is valid for any physical state or soln strength of the acid (Ref 10)... 

This crude product does not show any carbonyl absorption at 1710 cm.-1 in the infrared spectrum due to unreacted 2,3-cpoxycyclo-hexanone. 

It is expected, therefore, that the cyclic hexamer also exhibits a characteristic tendency to complex with cations. In fact, the addition of an acetonitrile solution of metal thiocyanates to a solution of the cyclic hexamer in the same solvent shifted the carbonyl absorption to a lower wave number46,52 The shift values depended upon the kind of metal ions present, and the largest shift value of 40 cm-1 was observed for barium thiocyanate (molar ratio of Ba2+/hexamer = 10). In addition to the shift of the carbonyl absorption, the intensities of the C—O-C stretching vibrations around 1200 cm-1 varied appreciably. 

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