Carbonyl Compounds
2,4-dinitrophenylhydrazine (2,4-DNP) which is also known as Brady’s reagent is used to identify the presence of carbonyl group in aliphatic as well as aromatic compounds. A solution of 2,4-DNP in sulphuric acid is added to the alcoholic solution of an organic compound (A) with molecular formula C4H8O. An orange-red precipitate is obtained. On warming Compound A with freshly prepared ammoniacal silver nitrate solution, a bright silver mirror is produced due to the formation of silver metal. Compound A is easily oxidised to carboxylic acid B with molecular formula C4H8O2 on treatment with common oxidising agents like nitric acid, potassium permanganate, potassium dichromate, etc. A on catalytic hydrogenation give a straight chain alcohol. Two moles of compound A in the presence of dilute alkali form a β-hydroxy aldehyde C which readily loses water to give α,β-unsaturated carbonyl compound D.
The IUPAC name of the compound C is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 2-ethyl-3-hydroxyhexanal
Compound C is the aldol formed from two molecules of butanal (compound A) in dilute alkali:
\( \displaystyle \ce{2CH3CH2CH2CHO} \xrightarrow{\text{dil. NaOH}} \ce{CH3CH2CH2-CH(OH)-CH(C2H5)-CHO} \)
To name it by the IUPAC system:
The aldehyde group has higher priority than the hydroxyl group, so it is the principal group (suffix -al) and its carbon is C-1.
The longest chain containing the CHO carbon has six carbon atoms: CHO (C-1), \( \ce{CH(C2H5)} \) (C-2), CH(OH) (C-3) and three more carbons. The parent name is hexanal.
The substituents are an ethyl group on C-2 and a hydroxy group on C-3, written in alphabetical order.
So the IUPAC name of C is 2-ethyl-3-hydroxyhexanal.