MHTCET 20 Apr 2026 Shift 2 Paper

Concept:Clemmensen reduction converts the carbonyl group of ketones into a methylene group, producing alkanes.Explanation:Alkanones are ketones containing the group $>\mathrm{C=O}$.To obtain the corresponding paraffin (alkane), the carbonyl oxygen must be removed and replaced by hydrogen atoms.Clemmensen reduction uses zinc amalgam ($\mathrm{Zn-Hg}$) and concentrated hydrochloric acid to perform this conversion.The general reaction is:$$R-\mathrm{CO}-R' \xrightarrow[\text{conc.}\ \mathrm{HCl}]{\mathrm{Zn-Hg}} R-\mathrm{CH}_{2}-R'$$For example, acetone is reduced to propane:$$\mathrm{CH}_{3}\mathrm{COCH}_{3} \xrightarrow[\text{conc.}\ \mathrm{HCl}]{\mathrm{Zn-Hg}} \mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{3}$$The other reactions are not suitable for this purpose.The Etard reaction converts methylbenzenes into benzaldehydes.The Rosenmund reduction converts acid chlorides into aldehydes.The Haloform reaction acts on methyl ketones to produce haloform, not alkanes.Hence, the preferential method for preparing paraffins from alkanones is Clemmensen reduction.Answer:Option A: Clemmensen reduction.