The present article deals with quantum chemical calculations of two nematogens namely; 4-Cyanophenyl-4'-n-Pentylbenzoate (CPPB), and 4-Cyanophenyl-4'-n-Pentoxybenzoate (CPPOB) by using the Density functional theory (DFT) and Hartree-Fock (HF) methods supplemented with basis set 6-31++G(d.p). The aromatic core with terminal cyano group confers a positive dielectric anisotropy, and high optical anisotropy. Cyano-substituent molecules possess great thermal and chemical stability, contributing many display and photonic applications. The observed vibrational spectra has resolved and assigned in detail for comparision with the molecules. It has been observed that global reactivity descriptors pertinant to intrinsic property of the system indicating a possible chemical change. Further, the frontier molecular orbital analysis for both the molecules has been carried out. It is important to note here that the method based on DFT predicts accurate molecular structures, and vibrational frequencies with moderate computational effort than HF method.