Question

What sequence of steps represents the best synthesis of 4-heptanol ${\left({CH}_3{CH}_2{CH}_2\right)}_{2}CHOH$?

• A. ${CH}_3{CH}_2{CH}_{2}MgBr$ (2 moles) + formaldehyde ($H_{2}C=O$) in diethyl ether followed by $H_3{O}^{+}$
• B. ${CH}_3{CH}_2{CH}_{2}MgBr$ + butanal (${CH}_3{CH}_2{CH}_{2}CH=O$) in diethyl ether followed by $H_3{O}^{+}$
• C. ${CH}_3{CH}_2{CH}_{2}MgBr$ + acetone$[{\left({CH}_3\right)}_{2}C=O$) in diethyl ether followed by $H_3{O}^{+}$
• D. ${\left({CH}_3{CH}_2{CH}_2\right)}_{2}CHMgBr$ + formaldehyde ($H_{2}C=O$) in diethyl ether followed by $H_3{O}^{+}$

Answer 1

The correct option is B ${CH}_3{CH}_2{CH}_{2}MgBr$ + butanal (${CH}_3{CH}_2{CH}_{2}CH=O$) in diethyl ether followed by $H_3{O}^{+}$

$O$

(A) $C{H}_{3}C{H}_{2}C{H}_{2}MgBr+H\stackrel{||}{C}H⟶\underset{\downarrow H_3{O}^{+}}{C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}OMgBr}$

$C{H}_{3}C{H}_{2}C{H}_3+C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}OH\underset{\left(ii\right)H^{+}}{\overset{\left(i\right)C{H}_{3}C{H}_{2}C{H}_{2}MgBr}{\to }}C{H}_{3}C{H}_{2}C{H}_{2}C{H}_{2}OH$

[Acid base reaction]

(B) $C{H}_{3}C{H}_{2}C{H}_{2}MgBr\underset{\left(ii\right)H_3{O}^{+}}{\overset{\left(i\right)C{H}_{3}C{H}_{2}C{H}_{2}CHO}{\to }}C{H}_{3}C{H}_{2}C{H}_2-\underset{|}{CH}-OH$

$\underset{4-heptanol}{C{H}_{3}C{H}_{2}C{H}_2}$

$O$ $C{H}_3$

(C) $C{H}_{3}C{H}_{2}C{H}_{2}MgBr\underset{\left(ii\right)H_3{O}^{+}}{\overset{\left(i\right)H_{3}C\stackrel{||}{C}C{H}_3}{\to }}C{H}_{3}C{H}_{2}C{H}_2-\underset{|}{\stackrel{|}{C}}-OH$

$\underset{2-Methyl-2-pentanol}{C{H}_3}$

(D) $(C{H}_{3}C{H}_{2}C{H}_2{)}_{2}CHMgBr\underset{\left(ii\right)H_3{O}^{+}}{\overset{\left(i\right)C{H}_2=O}{\to }}C{H}_3-C{H}_2-C{H}_2-\underset{|}{C}-CH-C{H}_{2}OH$

$H_{3}C{H}_{2}CC{H}_2$

Therefore the reaction B only gives our desired product $4-heptanol$. All the reactions involve treatment of Grignard reagent with carbonyl compounds giving alcohol after hydrolysis.