Ketones chemical reactivity

The chemistry of the carbonyl group is probably the single most important aspect of organic chemical reactivity Classes of compounds that contain the carbonyl group include many derived from carboxylic acids (acyl chlorides acid anhydrides esters and amides) as well as the two related classes discussed m this chapter aldehydes and ketones... 

Historically carbohydrates were once considered to be hydrates of carbon because their molecular formulas m many (but not all) cases correspond to C (H20) j It IS more realistic to define a carbohydrate as a polyhydroxy aldehyde or polyhydroxy ketone a point of view closer to structural reality and more suggestive of chemical reactivity... 

Many biological processes involve an "association" between two species in a step prior to some subsequent transformation. This association can take many forms. It can be a weak association of the attractive van der Waals type, or a stronger interaction such as a hydrogen bond. It can be an electrostatic attraction between a positively charged atom of one molecule and a negatively charged atom of another. Covalent bond formation between two species of complementary chemical reactivity represents an extreme kind of association. It often occurs in biological processes in which aldehydes or ketones react with amines via imine intermediates. 

The reaction of an amino group with an aldehyde or ketone leads to an imine, which, as we have just seen with aldolase, provides a splendid example of how to bond a carbonyl substrate to an enzyme, and yet maintain its chemical reactivity in terms of enolate anion chemistry. Another type of covalent interaction is quite commonly encountered, and this exploits the thiol group of cysteine. Thiols are more acidic than... 

Certain structural features, including whether it contains functional groups such as aldehydes, ketones, nitriles, or isocyanates, often define a class of chemicals. If information on the mechanism of action of a hazardous property of a chemical is not known, or if variances in the chemical s hazard through structural modification cannot be determined, then the assumption that certain chemically reactive functional groups can react similarly with the body or in the environment is often a good starting point in the process of evaluating the safety of solvents. 

As was the case for alkenes, alkyl substituents lower the enthalpy of the unsaturated molecule. Hence, ketones, with two R s, have lower enthalpies than aldehydes, with one R. The electron-releasing R s diminish the electrophilicity of the carbonyl C, lessening the chemical reactivity of ketones. Furthermore, the R s, especially large bulky ones, make approach of reactants to the C more difficult. 

Diisopropylbenzene Hydroperoxide — Fire Hazards Flash Point (deg. F) 175 Flammable Limits in Air (%) Data not available Fire Extinguishing Agents Foam, dry chemical, carbon dioxide Fire Extinguishing Agents Not to be Used Water may be ineffective Special Hazards of Combustion Products Flammable alcohol and ketone gases are formed in fires Behavior in Fire Burns with a flare effect. Containers may explode Ignition Temperature (deg. F) Data not available Electrical Hazard Data not available Burning Rate Data not available Chemical Reactivity Reactivity with Water No reaction Reactivity with Common Materials Aluminum, copper, brass, lead, zinc salts. 

We consider first how surfaces which are themselves not photosensitive can perturb chemical reactivity. First, the surface can influence diffusional motion of adsorbed substrates, intermediates or products. With preadsorbed substrates, one can probe the nature of motion of intermediates generated on the surface and search for differences in reactivity caused by surface confinement . When several photochemical precursors to benzyl radicals, e.g., benzyl phenylacetate, a dibenzyl ketone, or a dibenzyl sulfone, are irradiated as adsorbates on dry silica gel, singlet and triplet radical pairs are generated, Eq. (7). The extent of radical recombination observed requires... 

Fortunately, the rules of chemical reactivity and conformational analysis, coupled with the laws of thermodynamics, join forces to allow us to functionalize polyhydroxy aldehydes and ketones (aldoses and alduloses) in a selective and predictable fashion. 

An alternate explanation for the rapid rate of intersystem crossing in aromatic ketones is that 17,17 triplet levels lie between the singlets and the ,77 triplets,369 and Kearns has interpreted some T S absorption spectra as indicating two such low-lying triplets.105 However, even if two triplets do lie beneath the lowest singlet, the chemical reactivity of the lowest triplet would not be expected to change unless the two triplets were of mixed character. 

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