Question

Which ester on pyrolysis gives isobutylene
(A) $ {\rm{C}}{{\rm{H}}_3}{\rm{COOC}}{{\rm{H}}_2}{\rm{C}}{{\rm{H}}_2}{\rm{C}}{{\rm{H}}_3} $
(B) $ {\rm{C}}{{\rm{H}}_3} - {\rm{C}}{{\rm{H}}_2} - {\rm{C}}{{\rm{H}}_2} - {\rm{COO}} - {\rm{C}}{{\rm{H}}_3} $
(C) $ {\rm{C}}{{\rm{H}}_3}{\rm{COOC}}{{\rm{H}}_2} - {\rm{CH}}{\left( {{\rm{C}}{{\rm{H}}_3}} \right)_2} $
(D) All the above

Answer 1

Hint: An ester is a chemical compound formed from an acid (organic or inorganic) in which at least one –OH hydroxyl group is substituted by a –O– alkyl (alkoxy) group, as in the carboxylic acid and alcohol replacement reaction.

Complete answer:
Pyrolysis is the chemical decomposition of organic products at high temperatures in the absence of oxygen. Temperatures above 430 °C (800 °F) and pressure are common for the operation. It is an inevitable phenomenon that requires both a transition in physical phase and a change in chemical composition.
Lysis is a Greek word that means "breaking down." Pyrolysis of plastic is a chemical reaction. In the presence of the sun, this reaction entails the molecular fragmentation of larger molecules into smaller molecules. Pyrolysis is also referred to as thermal melting, cracking, thermolysis, depolymerization, among other words.
Ester Pyrolysis is a syn-elimination that produces an alkene, analogous to the Cope Elimination, which requires ß-hydrogens. A byproduct is the carboxylic acid that corresponds to the ester.
Only if the steric condition is not too demanding will the cyclic transition state be reached. According to Hofmann's Rule, steric results have the greatest impact on the result of Hofmann or related eliminations. The -hydrogen is ideally lost from the least hindered (least substituted) position $ {\rm{C}}{{\rm{H}}_3} > - {\rm{C}}{{\rm{H}}_2} - {\rm{R}} > - {\rm{CH}}\left( {{{\rm{R}}_2}} \right) $ .The substance alkene with the fewest substituents will win out.
Here
 $ {\rm{C}}{{\rm{H}}_3}{\rm{COOC}}{{\rm{H}}_2} - {\rm{CH}}{\left( {{\rm{C}}{{\rm{H}}_3}} \right)_2}{(C{H_3})_2}C = C{H_2} $
Isobutylene is formed
To get an iso group in the product we need to have the same iso group in the reactant side. Less substituted Hoffman product is formed.
Hence Option C is correct.

Note:
A hydrogen atom that is directly bound to a β carbon atom is known as β hydrogen. An ester with beta hydrogens. The presence of beta hydrogens in an alkyl bromide. Depending on the reference point, a beta hydrogen may also be an alpha hydrogen.