Animated Solution for Chemistry - Organic Chemistry: Major product of the following reaction is

Building the Monomer

Imagine you are an architect tasked with building a complex molecular structure. Our starting materials are 2-chloroacryloyl chloride and ethylenediamine. The first step in our blueprint is a classic nucleophilic acyl substitution.

In the presence of a base like triethylamine ($E{t}_{3}N$), the nucleophilic amine groups of ethylenediamine attack the highly electrophilic carbonyl carbons of the acid chloride. The triethylamine acts as a crucial acid scavenger, neutralizing the $HCl$ byproduct and driving the reaction forward. Because we have a diamine reacting with an excess of the acid chloride, both ends of the diamine react. This yields a symmetrical bis-amide intermediate known as N,N'-ethylenebis(2-chloroacrylamide).

Now, the real magic begins. We introduce a free radical initiator to trigger polymerization. Take a close look at our bis-amide intermediate: it possesses two polymerizable vinyl groups (the carbon-carbon double bonds). This presents a fascinating dilemma. Will the growing polymer chain react intermolecularly to form a linear chain, or will it react intramolecularly to form a ring (a process known as cyclopolymerization)?

To answer this, we must look at the kinetics and thermodynamics of ring formation. If the radical at one end of the monomer were to attack the double bond at the other end, it would have to form either an 8-membered or a 9-membered ring.

Thermodynamics Rules

Here is the catch: forming medium-sized rings (specifically 8 to 11 members) is notoriously difficult. These rings suffer from significant transannular strain (steric clashes across the ring) and an unfavorable entropy of activation. The ends of the molecule simply have a hard time finding each other in the right orientation.

Because intramolecular cyclization is so sluggish, the intermolecular propagation completely outcompetes it. The polymerization proceeds linearly through just one of the double bonds of each monomer unit. The other double bond is left completely intact, hanging off the main polymer backbone as a pendant group.

Therefore, the major product is a linear polymer adorned with these reactive pendant double bonds. In a real-world application, as the concentration of the polymer increases, these pendant groups will eventually react with other growing chains, creating a highly cross-linked, robust 3D network. This is precisely why such bis-acrylamide monomers are widely used as cross-linking agents in polymer chemistry!