We have performed a comprehensive geometrical, vibrational and electron topological analysis of hydrogen bonds in DNA base pairs involving canonical and rare tautomer's. Quantum chemical calculations at the MP2/6-31G(d,p) and DFT B3LYP/631G(d,p) levels of theory allowed to establish that CH...O contacts are real hydrogen bonds, whose strengths are close to 1 kcal/mol, i.e. exceed kT value at the room temperature.