Isomers of trimethylbenzene (TMB) are the important constituent chemicals used in a variety of industrial applications, including the production of synthetic resins, insecticides, dyes, pigments, and pharmaceuticals. However, these applications require them in their purest form, mandating them to separate from their mixtures. Due to the similar physicochemical properties of the TMB isomers, traditional methods such as cryogenic distillation are very energy-expensive. Thus, adsorption-based separation methods using nanoporous adsorbents such as zeolite are a cost-effective alternate. Such adsorption-based separation methods, however, require the isomers to exhibit significant differences in their adsorption and diffusion properties. In the present report, we carried out a thorough investigation of the structural, energetic, and dynamical properties of the three isomers of TMB in a faujasite-type zeolite NaY containing cage-like pores. Our results indicate that 1,2,4-TMB exhibits the most facile translational and out-of-plane rotational motions in contrast to the other two isomers. However, the in-plane rotational motions are seen to be more facile in 1,2,3-TMB compared with the other two isomers. It is evident from our analysis that the dynamics are dominantly driven by entropy. These results highlight the importance of the porous material in the case of the separation of a given hydrocarbon mixture.