Exploring C-H···O hydrogen bonds in dihydrocoumarin from combined vibrational spectroscopy and DFT calculations

► A combined vibrational spectroscopy and DFT calculations approach is performed. ► Presence of extra components in the carbonyl stretching mode band is observed. ► Analysis shows the co-existence of a Fermi resonance and C-H···O hydrogen bonds. ► A value of ΔH° = −8.4 ± 0.9 kJ mol−1 for the equilibrium process is established. ► Analysis shows that both methylene and aromatic C-H groups have a important role.