The separation of mixtures of isomers is a daunting task. It is found that perethylated pillar[5]arene can separate trans-dichloroethene from its cis isomer. This work deals with the host-guest interactions and the selective separation of trans dihaloethene over cis-dihaloethene using perethylated pillar[5]arene. From this work, one can understand why only trans dihaloethenes are encapsulated while cis-dihaloethenes are not. Initially, molecular dynamics was performed at different picoseconds for the 1 : 1 inclusion complexes. In addition to these, MD simulation on a mixture of cis & trans isomers has also been done to ensure the preferential selectivity of perethylated pillar[5]arene towards the trans isomer. A brief DFT study was carried out to explain the better encapsulation of trans-dihaloethene in perethylated pillar[5]arene. Frontier molecular orbital analysis provides information on the stability and reactivity of the dihaloethene isomers. The non-covalent interactions between the host and the guest are determined using the quantum theory of atoms in molecules. Energy decomposition analysis indicates that the solvent phase influences the binding energy to a greater extent compared to the gas phase and orbital interaction energies are reduced substantially upon moving from the gas to the solvent phase. The Gibbs free energy indicates that these isomers readily form inclusion complexes with perethylated pillar[5]arene. Overall our results provide valuable information on the non-covalent interactions that drive the inclusion phenomenon in these host-guest systems.