<p>A comprehensive investigation of the linear and nonlinear optical (NLO) properties and reactivity of six ethanamide derivatives was performed at the DFT/CAM-B3LYP level. The linear optical parameters, including the dipole moment, mean polarizability, and polarizability anisotropy, were computed to assess the electronic polarizability and molecular anisotropy. The NLO properties were evaluated by calculating the total first hyperpolarizability <i>β</i>_tot, the electric-field-induced second harmonic generation <i>β</i>_//, and the hyper-Rayleigh scattering <i>β</i>_HRS. Mulliken atomic charge, frontier molecular orbitals, and their energy gaps are also predicted and analyzed for these ethanamides. The NLO results demonstrate variations in polarizabilities and first hyperpolarizabilities with structural modifications, revealing the roles of substituent effects and conjugation patterns in NLO responses. Ethanamides with -NO₂, -CH₃, and -OCH₃ show strong <i>β</i>_tot (958.65, 911.48, and 890.32 a.u.), respectively. The correlations are well marked between <i>β</i>_tot and the energy gap, and between <i>β</i>_HRS and <i>β</i>_//. The atomic charge values suggest extensive charge delocalization in Acet@F. The same for the ethanamide Acet@NO₂ with the strong attractor group NO₂. The results position thiazole-containing ethanamides as promising candidates for the development of optoelectronic and photonic devices.</p> Graphical Abstract <p></p>