The complex formed between methyl chloride and formic acid provides a suitable model system for exploring the nature and characteristics of weak as well as unconventional hydrogen bonding interactions. In the present study, four minima corresponding to distinct van der Waals complexes of formic acid HCOOH and methyl chloride CH3Cl are considered. DFT study using B3LYP 6 311 G level of theory has been used to find the minima of the four van der Waals complex. Binding and activation energies were evaluated at the same level of theory. RHF and RMP2 level calculations were also performed to present a comparative account. The four optimized minima are connected through low lying energy barriers of approximately 0.9–2.6 kcal mol 1, suggesting that facile interconversion between these structures is possible. The study highlights the significance of cyclic arrangements in which multiple weak hydrogen bonds contribute to the overall structural stability, with the combined stabilization being enhanced through cooperative interactions among these hydrogen bonds. The findings provide deeper insight into the nature and significance of unconventional hydrogen bonding interactions. B3LYP, van der Waals complex, binding energy, activation energy. 461-466 Issue-5 Volume-10 Arjun Singh | Jyoti Tyagi | Sanjeev Kumar Mishra