<Li> Nucleophilic abstraction is used to produce carbon dioxide </Li> <P> α, β - Unsaturated carbonyl compounds are an important class of carbonyl compounds with the general structure (O = CR) − C = C - R; for example enones and enals . In these compounds the carbonyl group is conjugated with an alkene (hence the adjective unsaturated), from which they derive special properties . Unlike the case for simple carbonyls, α, β - unsaturated carbonyl compounds are often attacked by nucleophiles at the β carbon . This pattern of reactivity is called vinylogous . Examples of unsaturated carbonyls are acrolein (propenal), mesityl oxide, acrylic acid, and maleic acid . Unsaturated carbonyls can be prepared in the laboratory in an aldol reaction and in the Perkin reaction . </P> <P> The carbonyl group draws electrons away from the alkene, and the alkene group is, therefore, deactivated towards an electrophile, such as bromine or hydrochloric acid . As a general rule with asymmetric electrophiles, hydrogen attaches itself at the α - position in an electrophilic addition . On the other hand, these compounds are activated towards nucleophiles in nucleophilic conjugate addition . </P> <P> Since α, β - unsaturated compounds are electrophiles, many α, β - unsaturated carbonyl compounds are toxic, mutagenic and carcinogenic . DNA can attack the β carbon and thus be alkylated . However, the endogenous scavenger compound glutathione naturally protects from toxic electrophiles in the body . Some drugs (amifostine, N - acetylcysteine) containing thiol group may protect biomolecules from such harmful alkylation </P>

Which class of molecules contains the carbonyl group co