Question

(a) Write the chemical reaction involved in Wolff- Kishner reduction.
(b) Arrange the following in the increasing order of their reactivity towards nucleophilic addition reaction:
${{C}_{6}}{{H}_{5}}COC{{H}_{3}},C{{H}_{3}}CHO,C{{H}_{3}}COC{{H}_{3}}$
(c) Why do carboxylic acids not give reactions of carbonyl groups?
(d) Write the product in the following reaction:
$C{{H}_{3}}C{{H}_{2}}CH=CHC{{H}_{2}}CN\xrightarrow[{{H}_{2}}O]{{{\left( i-Bu \right)}_{2}}AlH}$
(e) A and B are two functional isomers of compound ${{C}_{3}}{{H}_{6}}O$ . On heating with $NaOH$ and ${{I}_{2}}$ , isomer B forms yellow precipitate of iodoform whereas isomer A does not form any precipitate. Write the formula of A and B.

Answer 1

Hint:A chemical reaction is defined as a process in which the bond of the reactant molecules breaks and results in the formation of a new bond that gives a product molecule. It is a reaction in which two or more molecules interact and form new substances.

Complete step-by-step answer: Let us discuss the above questions one by one:
(a) Wolff kishner reduction is a chemical name reaction in which aldehydes and ketones are converted into an alkane in presence of hydrazine, base and thermal conditions. When aldehydes or ketones are heated with hydrazine and potassium hydroxide in ethylene glycol, it results in the formation of alkanes.
Let us see the chemical reaction:
$R-CO-{{R}^{'}}\xrightarrow[KOH,\Delta ]{N{{H}_{2}}-N{{H}_{2}},{{H}_{2}}O}RC{{H}_{2}}-{{R}^{'}}+{{N}_{2}}$
(b) As we know that, aldehydes are more reactive than alcohol because aldehydes are less hindered than ketones. Aliphatic ketones are more reactive than aromatic ketones because aromatic ketoses have delocalisation of electrons. Therefore the reactivity order can be written as:
${{C}_{6}}{{H}_{5}}COC{{H}_{3}}(c)Carboxylic acids do not give reactions to carbonyl groups because the lone pair of electrons on oxygen atoms of the $-OH$ group of carboxylic acid is less electrophilic than the carbonyl group of ketones and aldehydes.
(d) Let us write the product of the given reaction:
$C{{H}_{3}}C{{H}_{2}}CH=CHC{{H}_{2}}CN\xrightarrow[{{H}_{2}}O]{{{\left( i-Bu \right)}_{2}}AlH}C{{H}_{3}}C{{H}_{2}}CH=CHC{{H}_{2}}CHO$
(e) B is a methyl ketone as it forms yellow precipitate of iodoform, that means it undergoes a haloform reaction. hence, B is acetone $C{{H}_{3}}COC{{H}_{3}}$ . The isomer A does not form any precipitate, therefore it will not have any methyl ketone. Hence isomer A is propanal $C{{H}_{3}}C{{H}_{2}}CHO$ .

Note:It is to note that nucleophilic addition reaction is defined as reaction where a compound that contains electrophilic double or triple bond reacts with a nucleophile so that it can break the double or triple bond. It converts carbonyl groups into a variety of functional groups.