The IR spectra of intramolecular hydrogen bonds in ortho Mannich bases have been measured in the gas phase and in diluted CCl₄ solutions. It is demonstrated that the intramolecular hydrogen bonds are stable both in the gas phase and in CCl₄ solutions. The hydrogen bonds in the gas phase are weaker but the ν_s(OH) bands are still broad with a halfwidth of about 400-500 cm^-1. It demonstrates that the coupling with internal modes of a molecule is a sufficient condition for such band broadening. Spectral moments of ν_s(OH) bands were determined and correlated with ΔpK_a values both in the gas phase and in CCl₄ solutions.