The i.r. spectra of adducts of some trihalogenoacetic acids with dimethyl selenoxide and of dichloroacetic acid with trimethylarsine oxide, and trimethylamine oxide, indicate very strong hydrogen bonding with proton transfer. Besides an OH+ stretching band near 2200 cm.–1 and the deformation bands near 1350 and 950 cm.–1 they show additional protonic bands close to the antisymmetric band of the CO2– group. The corresponding vibration interacts by Fermi resonance with ν2(CO2–) which explains the shift of the latter band on deuteriation.
