Abstarct: In this thesis, molecular structure, vibrational spectrum and proton chemical shift of Naringenin (NRG) were investigated by calculations Density functional theory (DFT) at M062X/6-311 ++ G**. The nature of intramolecular hydrogen bonding of chelated ring was studied. Then intramolecular hydrogen bonding of a number of flavonoids including Chrysin (CRS), Pinocembrin (PCB), Galangin (GLG), Pinobanksin (PBK), Apigenin (APG), Narigenin (NRG), Luteolin (LTL), Eriodictyol (EDC), Morin (MRN) And Dihydromorine (D-MRN) were also compared with using vibrational frequencies, chemical shift, QTAIM and NBO parameters. The relationship between intramolecular hydrogen bonding and antioxidant properties was investigated by bond dissociation energy for hydrogen abstraction (H-BDE). To determine the chemical activity of these compounds, general reactivity parameters and local chemical properties including MEP was studied at the M062X / 6-311 ++ G ** level of theory. The results showed that all the studied flavonoids have a moderate hydrogen bond with a partial covalent nature. Chrysin (CRS), Apigenin (APG) and luteolin (LTL) are the strongest hydrogen bonds and Pinobanxin (PBK) and Dihydromorin(D-MRN) has the weakest hydrogen bond among studied flavonoids. Also, it was shown with increasing intramolecular hydrogen bond strength, the H-BDE parameter increases and its antioxidant properties decrease. Comparison of the parameters related to reactivity properties showed that all above mentioned flavonoids have low hardness so they can interact with soft molecules. Among these studied molecules, NRG and PCB show less reactivity and GLG show more reactivity with other molecules than other studied compounds