## 1 Introduction  
It is well recognized that conjugated organic systems possessing \(\pi\)-electrons, which are typically delocalized, exhibit varying degrees of stability, influenced by their structural and electronic characteristics. In heterocyclic compounds, factors such as the nature and position of substituents, intra- and intermolecular interactions, and ionization and protonation/deprotonation processes play a pivotal role in modulating electron delocalization and, in turn, the stability and reactivity of these molecules. Flavonoid compounds, a prominent class of polyphenic substances, have gained significant attention due to their diverse biological activities, including antioxidant, anti-inflammatory, and anticancer properties [1]. Recent studies have also identified several flavonoids as inhibitors of viral replication, making them promising candidates for therapeutic intervention in diseases such as COVID-19 [2]. Notably, compounds like 3-hydroxyflavone (3-HF) have demonstrated a unique combination of chemical features and bioactivity, meriting further exploration of their electronic structures. Flavonoids are a structurally diverse group of naturally occurring compounds, widely distributed in plants and dietary sources [3]. They share a common 15-carbon skeleton comprising two benzene rings (A- and B-rings) connected by a heterocyclic pyran ring (C-ring) (see Figure 1). Flavonoids are classified into subclasses, including flavones, flavanones, flavonoids, isoflav, and anthocyanins, based on their structural variations, such as substitutions and the degree of oxidation in the C-ring [3]. Among these, flavones are characterized by the absence of oxygenation at the C3 position [4], a double bond between C2 and C3, and a ketone group at C4 [5]. The position and number of hydroxyl groups on the flavone backbone are critical determinants of their electron delocalization, hydrogen-bonding capabilities, and radical-scavenging activity, which underpin their biological function. In mono-hydroxyflavones, subtle changes in hydroxyl placement can lead to pronounced differences in chemical reactivity and stability--highlighted by the unique behavior of 3-HF, which features intramolecular hydrogen bonding. Due to hydroxylation at the C3 position of the C-ring, 3-HF is neither the most stable nor the least stable mono-hydroxyflavone. Previous studies have found that most naturally occurring flavones have a hydroxyl group at the C5 position of the A-ring, while hydroxylation at other positions, such as C7 (A-ring) or C3\({}^{\prime}\) and C4\({}^{\prime}\) (B-ring), varies across different plant species [5]. While experimental spectroscopic techniques offer foundational insight into the structural properties of flavonoids, they often depend on empirical or semi-empirical models fitted to natural derivatives, potentially overlooking subtle electronic effects in synthetic or non-naturally occurring isomers [6; 7]. In this context, quantum mechanical (QM) methods, such as density functional theory (DFT), provide a robust framework for elucidating the structure-property relationships of flavones and their analogues [8; 9; 10]. These methods allow for a first-principle analysis of the electron density distribution, conjugation, orbital energetics, and solvation effects--essential for understanding how positional isomerism influences molecular properties. This is particularly relevant for non-natural derivatives like 8-hydroxyflavone [7], where the hydroxyl substitution at an atypical position significantly alters the electronic structure and intramolecular interactions compared to biosynthetically preferred isomers. A QM approach thus enables predictive insight beyond experimental limitations, offering a deeper understanding of how structural variations in flavone derivatives impact their stability and functional potential. In this study, we explored the electronic structure of flavone and its eight mono-hydroxyflavone derivatives (n-HFs) using density functional theory (DFT)-calculated NMR chemical shifts.