Post-translational modifications (PTMs) such as nitration of Tyr (Y) residues and di-tyrosine (DT) formation are known to impact the aggregation behavior of α-synuclein (α-syn), a protein closely linked to Parkinson’s disease. Using tetranitromethane (TNM) as a model nitrating agent, we systematically investigated the chemical modifications of α-syn and their consequences for aggregation. Mass spectrometry analysis revealed selective nitration of all four Tyr residues, with Y39 and Y125 being most susceptible. DT crosslinks were also observed, primarily involving Y39, but were disfavored at higher TNM concentrations, indicating competition between nitration and crosslinking pathways.