Question

$0.44\, g$ of a monohydric alcohol when added to methyl magnesium iodide in ether liberates at $S.T.P.,$ $112\, cm^3$ of methane. With $PCC$ the same alcohol forms a carbonyl compound that answers silver mirror test. The monohydric alcohol is

• A. ${(CH_3)_3}C - CH_2OH$
• B. ${(CH_3)_2}CH - CH_2OH$
• C.
• D.

Answer 1

Answer: (A)

${(CH_3)_3}C - CH_2OH$

Answer 2

This problem includes conceptual mixing of mole concept, Tollen's test, reaction if carbonyl compound and function of Grignard reagent. Follow the steps given below to solve this questions. Calculate the molecular mass of a alcohol using the concept of mole concept. Now use the concept of Tollen's test to identify the correct substrate as among aldehyde and ketone only aldehyde undergo Tollen's test. Aldehyde can be prepared by the reaction of primary alcohol with PCC. $\therefore$ Molecular mass of alcohol $=\frac{0.44 \times 22400}{112}=88$ Since, alcohol oxidised with PCC [pyridinium chloro chromate or Corey's reagent $\left.C _{5} H _{5} NH ^{+} CrO _{3} Cl ^{-}\right]$ to form a carbonyl compound (aldehyde), which gives positive silver mirror test hence carbonyl compound must be an aldehyde therefore it must be a primary alcohol. $\underset{m=88}{(CH _{3})_{3}} C - CH _{2} OH \stackrel{\text { PCC}}{\longrightarrow}\left( CH _{3}\right)_{3} C - CHO$ $\underset{m=74}{(CH _{3})_{2}} CH - CH _{2} OH \stackrel{\text { PCC }}{\longrightarrow}\left( CH _{3}\right)_{2} CH - CHO$ In the given options, (b) and (c) are primary alcohols having molecular masses 88 and 74 respectively. Hence only (b) will be the correct choice.