<![CDATA[Free radicals are one of the main causes of cell damage that triggers various chronic diseases, so the use of natural antioxidants from the monoterpenoid group of tropical plants continues to be developed. This study aims to evaluate the chemical reactivity, kinetic stability, and theoretical free radical scavenging capacity of three monoterpenoid compounds (Eugenol, Menthol, and Thymol) compared with Ascorbic Acid as a positive control. The method used is computational chemistry simulation based on Density Functional Theory (DFT) with the B3LYP/6-31G(d) level of theory. The global quantum descriptor parameters analyzed include HOMO energy (EHOMO), LUMO energy (ELUMO), energy gap (ΔEgap) and global electrophilicity index (ω), which are supported by Molecular Electrostatic Potential (MEP) mapping. The results of computational calculations show that Eugenol has the highest EHOMO value (-5,539412 eV) and the smallest ΔEgap of 4,721751 eV. This indicates that Eugenol is kinetically the most reactive and most easily species compared to Thymol (-5,973139 eV), Ascorbic Acid (-6,424009 Ev), and Menthol (-6,424009 eV). The presence of aromatic rings and delocalized (π) electron systems in Eugenol has been shown to stabilize phenoxyl radicals through resonance effects. MEP visualization confirms the presence of electron-rich nucleophilic active centers (dark red) around the oxygen atoms of the hydroxyl (-OH) and methoxy (OCH3) groups that are ready to interact via a hydrogen atom transfer mechanism. In contrast, Menthol shows the lowest efficiency (ΔEgap= 6,499870 eV) because its structure is saturated without conjugation (π). This theoretical study provides a fundamental basis that phenolic functional groups and conjugated systems are crucial in predicting the in silico antioxidant activity of monoterpenoids.]]>
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