Carbonyl functional groups aldehydes

Carbonyl functional groups are the easiest to identify of all IR absorptions because of their sharp, intense peak in the range 1670 to 1780 cm-1. Most important, the exact position of absorption within the range can often be used to identify the exact kind ot carbonyl functional group—aldehyde, ketone, ester, and so forth. 

Monosaccharides are identified by their carbonyl functional group (aldehyde or ketone) and by the number of carbon atoms they contain. The simplest monosaccharides are the two trioses glyceraldehyde (an aldotriose) and dihydroxyacetone (aketotriose). Four-, five-, six-, and seven-carbon-containing monosaccharides are called tet-roses, pentoses, hexoses, and heptoses, respectively. Structures of some monosaccharides are shown in Figure 9-1. All monosaccharides, with the exception of dihydroxyacetone, contain at least one asymmetrical or chiral carbon atom, and therefore two or more stereoisomers are... 

Although carbohydrates exist almost entirely as cyclic hemiacetals m aqueous solution they are m rapid equilibrium with their open chain forms and most of the reagents that react with simple aldehydes and ketones react m an analogous way with the carbonyl functional groups of carbohydrates... 

Hydro carbonylation of olefins, hydroformylation, hydroesterification and hy-droxycarbonylation are reactions which appear to be of particular interest. Indeed, they allow the simultaneous creation of a new C - C bond as well as the introduction of a functional group (aldehyde, ester and acids). One or two new stereogenic centres can thus be formed at the same time (Scheme 26). Despite the difficulty of using high carbon monoxide pressure, the aheady existing industrial processes prove that such reactions can be performed on a very large scale [107]. 

Aldehydes and ketones both have the carbonyl functional group. An aldehyde is an organic compound that has a double-bonded oxygen on the last carbon of a carbon chain. The functional group for an aldehyde is... 

Since aldehydes and ketones both possess the carbonyl functional group, they undergo similar chemical reactions. 

The name aldol is derived from the names of the two functional groups, aldehyde and alcohol, present in the products. The aldol and ketol readily lose water to give a,p-unsaturated carbonyl compounds which are aldol condensation products and the reaction is called Aldol condensation. Though ketones give ketols (compounds containing a keto and alcohol groups), the general name aldol condensation still applies to the reactions of ketones due to their similarity with aldehydes. 

Aldehydes and ketones both contain the carbonyl functional group ... 

Aluminum atom reactions are relevant to interfacial chemistry associated with aluminum-polyimide junctions. Al deposited under ultra high vacuum will reduce surface carbonyl functional groups (22). MVS co-condensation experiments show that besides ketones, aldehydes and epoxides, atomic aluminum will deoxygenate ethers. Chapter 7 of the monograph by Klabunde (12) includes tables of deoxygenation products of a variety of cyclic and acyclic ketones and ethers. 

The Homer-Wadsworth-Emmons reaction is among the most important reactions for effecting a two-carbon chain elongation of a carbonyl functional group - " It can be described as a general synthetic protocol for the conversion of aldehydes and ketones into aji-unsaturated carbonyl compounds and their derivatives " ... 

The carbonyl functional group provides an electrophilic site for nucleophilic attack. As none of the naturally occurring amino acids contains a ketone or aldehyde moiety, it is not possible for a protein-bound carbonyl group to be present at an enzyme active site, unless it is provided by a cofactor. The most commonly seen reactive carbonyl group in enzymes is that provided by the pyridoxal phosphate cofactor which is derived from vitamin B6." The carbonyl serves as a site for covalent adduct formation with a nucleophilic substrate, often an amine or the amino group of amino acid substrates. An alternative strategy for introduction of a reactive carbonyl at an enzyme active sight has been described for a class of enzymes that possess a covalent pyruvoyl cofactor. 

Solution A characteristic of both ketones and aldehydes is the carbonyl functional group they possess. Thus, to characterize and identify ketones and aldehydes, reactions with the carbonyls are often done. Since oxygen is more electronegative, (electron-attracting) than carbon, the carbonyl carbon becomes susceptible to nucleophilic attack. Hydroxylamine, derived from its hydrochloride salt, can act as a nucleophilic reagent. 

Organic compounds containing a carbonyl functional group, J C=0, such as aldehydes, ketones, esters, and carboxylic acids, exhibit a low order of toxicity. The lower aldehydes, such as formaldehyde, acetaldehyde, and acrolein, are severe irritants to the eyes and respiratory tract. Acrolein is a severe lachry-mator. Lower carboxylic acids are corrosive substances. Formic acid is a poison, but the toxic effects arise as a result of lowering of the blood pH below normal levels and have little to do with the carbonyl group in the molecule. 

A number of naturally occurring aldehydes and ketones play important roles within living systems. The carbonyl functional group is fairly common in biological compounds. For example, progesterone and testosterone, female and male sex hormones, respectively, are both ketones. 

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 for simple ketones, aldehydes, and acids as a standard for comparison. Appendix 2 gives a more complete table of characteristic IR frequencies. 

Aldehydes, ketones, ketosteroids and sugars contain the carbonyl function group. In earlier studies on the HPLC separation of these compunds, 2,4-dinitrophenyl-hydrazine was widely used as a derivatization reagent to enhance their detectivity. 2,4-DNPH reacts with carbonyl groups to form 2,4-dinitrophenylhydrazones (Figure 14). 

---