Esters infrared frequencies

The infrared spectra of solid phospholipids vary due to the occurrence of polymorphism. The ester carbonyl frequency and bands between 670 and 1050 cm may shift due to the variations in the crystal structure arising from different polymorphs. 

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. 

Table 2 Infrared carbonyl absorption frequencies (CHC13), 13C and selected 15N chemical shiftsa (CDC13) for 7V-acyloxy-7V-alkoxyamides (R1ON(OCOR2)COR3) and precursor hydroxamic esters... 

One of tire distinguishing physical characteristics of the cephalosporins is the infrared stretching frequency of the /i-lactam carbonyl. This absorption occurs at higher frequencies (1770-1815 cm-1) than those of either normal secondary amides (1504-1695 cm-1) or ester carbonyl groups (1720-1780 cm-1). 

Collette (1992) proposed a novel approach to developing and applying QSARs for the alkaline hydrolysis of carboxylic acid esters using infrared (IR) spectroscopic data. The concept is to extend QSARs to a larger and more diverse group of organic compounds by including the structural information encoded in IR spectra. Such data are available from spectral data bases, but even in the absence of literature data, IR frequencies are readily measurable. 

Infrared spectra of (a) ethyl octanoate and (b) methyl benzoate. The carbonyl stretching frequency of simple esters is around 1735 cm-1 and that of conjugated esters is around 1710-1725 cm-1. 

Hyponitrous acid. In contrast to nitrous and nitric acids, hyponitrous acid crystallizes from ether as colourless crystals which easily decompose, explosively if heated. The detailed molecular structure of this acid has not been determined, but it is known that the molecular weights of the free acid and its esters correspond to the double formula, H2N2O2, that it is decomposed by sulphuric acid to N2O, and that it can be reduced to hydrazine, H2N-NH2. Infrared and Raman studies show conclusively that the hyponitrite ion has the trans configuration (a), but the N-N frequency suggests that the central bond has an order of rather less than two. ... 

Aldehydes Amides Carboxylic acid anhydrides Carboxylic acids Esters Ketones and functional groups, 56 infrared absorption frequencies, 519,... 

Herriott used the phosphorus epimers of 0-(-)-menthyl methylphenylphosphinoth-ioate to demonstrate the almost quantitative stereospecificity in the reaction with mCPBA by contrast, the use of trifluoroperoxyacetic acid was less successful, with a retention to inversion ratio of 21 79. A further feature in favour of mCPBA is the independence of its activity relative to solvent. Other extensive correlations were made by Inch and coworkers during investigations into the stereochemistry of displacement reactions at phosphorus in compounds based on a carbohydrate template 81 by means of structural assignments based on infrared absorption frequencies for the P=0 bond together with P NMR chemical shifts, they showed that mCPBA oxidation of thiophosphoryl or selenophosphoryl bonds (A or B = =S or =Se, B or A = Me or Ph) occurred highly stereoselectively with the formation of the phosphonate ester with retained stereochemistry ... 

We calculate an index of hydrogen deficiency of three. A quick glance at the infrared spectrum reveals the source of unsaturation implied by an index of three a nitrile group at 2260 cm (index = two) and a carbonyl group at 1747 cm (index = one). The frequency of the carbonyl absorption indicates an unconjugated ester. The appearance of several strong C—O bands near 1200 cm confirms the presence of an ester functional group. We can rule out a CM2 bond because they usually absorb at a lower value (2150 cm ) and have a weaker intensity than compounds that contain C=N. 

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