Ketones infrared spectrum

Qualitative tests may be performed by selective chemical reactions or with the use of instrumentation. The formation of a white precipitate when adding a solution of silver nitrate to a dissolved sample indicates the presence of chloride. Certain chemical reactions will produce colors to indicate the presence of classes of organic compounds, for example, ketones. Infrared spectra will give fingerprints of organic compounds or their functional groups. 

That the 17-hydroxyl group was secondary and in a five membered ring was shown by its Oppenauer oxidation to a ketone (infrared spectrum indicative of a cyclopentanone). Reduction of this ketone would have been expected to proceed by addition of the hydrogen on the unhindered face that is the one before the... 

A second reason why AI is of value to scientists is that it offers powerful tools to cope with complexity. In favorable circumstances, the solutions to problems can be expressed by rules or by a well-defined, possibly trivial, model. If we want to know whether a compound contains a carbonyl group, we could record its infrared spectrum and check for a peak near 1760 cm1. The spectrum, paired with the rule that ketones generally show an absorption in this region, is all that we need. But other correlations are more difficult to express by rules or parametrically. What makes a good wine We may (or may not) be able to recognize a superior wine by its taste, but would have considerable difficulty in determining whether a wine is good, or even if it is palatable, if all we had to go on was a list of the chemicals of which it is comprised. 

The infrared spectrum of erythromycin is commonly used for its identification. Figure 2 shows the spectrum of a 75 mg./ml. chloroform solution. The bands at 1685 and 1730 cm- are due to the ketone carbonyl and the lactone carbonyl, respectively. The absorption peaks between 1000 and 1200 cm-1 are due to the ethers and amine functions. The CH2 bending is evidenced by peaks between 1340 and 1460 cm-, and alkane stretching peaks appear between 2780 and 3020 cm-. Hydrogen bonded OH and water appear as bands between 3400 and 3700 cm-1. 

Figure 14.5. Infrared spectra of a ketone, upper spectrum, and aldehyde. Both have strong =0 absorption bands. Hexanal has a chain of -CH2 groups and -CH3 group, and thus the strong absorption just less than 3000 cm"1. 

Figure 4 illustrates the infrared spectrum for a sample of PPE. The absorptions of the peaks at 3.4, 6.9 and 7.3 pm were assigned to C-H stretch and C-H bending frequencies in CH2 and CH3 (33). These absorptions are proportional to the surface density of deposited ethane (16). However, the absorptions at photons near 10 pm are attributable to OH deformations and CO stretchings of alcoholic groups and vibrations of alkyl ketones (22). They also indicate the existence of branches in unsaturated chain (33). 

Attempts were made to reduce any aldehyde and ketone function with sodium borohydride. A 1.5-gram sample was weighed into a 100-ml. reaction flask and suspended in 10 ml. of methanol. A solution of 0.3 gram of sodium borohydride in 25 ml. of 0.1 IV sodium hydroxide was added to the sample over a period of 15 minutes. The mixture was refluxed under nitrogen for 6 hours, filtered, and washed thoroughly with water. The amount of aldehyde and ketone was estimated by the decrease in the 5.8 micron peak in the infrared spectrum of the treated sample as compared with the untreated sample. 

If the unknown compound gives a positive test with 2,4-dinitrophenylhydrazine it then becomes necessary to decide whether it is an aldehyde or a ketone. The infrared spectrum of the compound should be very informative both aldehydes and ketones show strong absorption at 1740-1700cm-1 (C=0 str.), but only aldehydes exhibit two absorption bands at about 2720 and 2820 cm-1... 

If the unknown, neutral, oxygen-containing compound does not give the class reactions for aldehydes, ketones, esters and anhydrides, it is probably either an alcohol or an ether. Alcohols are readily identified by the intense characteristic hydroxyl adsorption which occurs as a broad band in the infrared spectrum at 3600-3300 cm-1 (O—H str.). In the nuclear magnetic resonance spectrum, the adsorption by the proton in the hydroxyl group gives rise to a broad peak the chemical shift of which is rather variable the peak disappears on deuteration. 

The band at 1725 cm-1 in the infrared spectrum is due to a carbonyl group, probably a ketone. The quartet-triplet pattern in the NMR spectrum suggests an ethyl group. The compound is 3-pentanone ... 

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. 

---