Ketonic groups infrared spectroscopy

In the literature, LB films of chlorophyll a have been investigated by many techniques [21,27,28]. In particular, Chapados et al. [29] have studied the aggregation state of chlorophyll a in LB films with electronic and infrared spectroscopies. Their results suggest many points. First, immediately after the fabrication of the film (time zero) the ketone group C = 0 of one chlorophyll a molecule links to the magnesium of an adjacent chlorophyll a molecule to form a dimer. Each dimer interacts via water with another dimer to... 

The widespread use of infrared spectroscopy at that time was probably due to the observation that many chemical groups absorb in a very narrow range of frequency. Furthermore, within this frequency range, the observed frequency may be correlated to specific chemical structures. For example, aldehydes can be differentiated from ketones by the characteristic stretching frequency of the carbonyl group near 1700 cm-1, and the spectral pattern may be likened to a molecular fingerprint. ... 

Different types of carbonyl groups give characteristic strong absorptions at different positions in the infrared spectrum. As a result, infrared spectroscopy is often the best method to detect and differentiate these carboxylic acid derivatives. Table 21-3 summarizes the characteristic IR absorptions of carbonyl functional groups. As in Chapter 12, we are using about 1710 cm-1 for simple ketones and acids as a standard for comparison. Appendix 2 gives a more complete table of characteristic IR frequencies. 

Infrared spectroscopy is extremely useful for identifying aldehydes and ketones. Carbonyl groups absarh In the JR range 1660-1770 cm . with the exact position highly diagnostic of the kind of carbonyl up... 

Results of infrared spectroscopy studies have confirmed that COOH groups, or more precisely carboxylate (COO—), play a prominent role in the complexing of metal ions by humic and fulvic acids. Some evidence indicates that OH, C=0, and NH groups may also be involved (Vinkler et al., 1976 Boyd et al., 1979 Piccolo and Stevenson, 1981). The suggestion has been made (Piccolo and Stevenson, 1981) that, in addition to the above, complexes may be formed with conjugated ketonic structures, according to the following reactions ... 

Infrared spectroscopy IR and Fourier transform infrared (FTIR) spectra of humic substances show bands at 3400 cm (H bonding OFI), 2990 cm (aliphatic C-FI), 1725 cm(C = 0 of CO2H, C = 0 of ketone), 1630 cm (aromatic C = C, C = 0 of carbonyl, COO or quinone), 1450 cm (aliphatic C-H), 1400 cm - (COO ) and 1200 cm (C-O or OH of CO2H). The bands are usually broad due to overlapping of individual absorbances. While IR and FTIR provide worthwhile information about functional groups, they reveal little about the chemical structure of humic substances. FTIR and diffuse reflectance infrared Fourier transform (DRIFT) are the techniques most widely used. 

Sodium hypochlorite in acetic acid is an oxidizing agent capable of oxidizing alcohols to the corresponding aldehydes or ketones. In this experiment, you will oxidize a diol, 2-ethyl-l,3-hexanediol (1) and then use infrared spectroscopy to determine which of the alcohol functional groups was oxidized. 

You will determine whether the oxidation occurred selectively (and which functional group was oxidized) or whether both functional groups were oxidized at the same time. The possible outcomes of the oxidation are shown in the figure. If only the primary alcohol is oxidized, the aldehyde (2) will be formed if only the secondary alcohol is oxidized, the ketone (3) will be the product. If both alcohol functional groups are oxidized, compound (4) will be observed. Your assignment will be to use infrared spectroscopy to determine the structure of the product and decide which of these three possible outcomes actually takes place. 

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