Structure, and infrared and ultraviolet spectra of protonated dimethylacetamide

Abstract

The X-ray crystal structure of the title compound was determined by the heavy-atom method from diffractometer data and refined to R 0.052 for 621 independent reflections. Crystals of NN′-dimethylacetamide hydrochloride (NN′-dimethylacetamidonium chloride) are monoclinic, space group P2₁ with Z= 2 in a unit cell of dimensions a= 7.343(7), b= 6.890(7), c= 6.765(7), Å,β= 97.2(1)°. A difference-Fourier synthesis revealed the site of protonation of the amide to be the oxygen atom, confirming much indirect evidence. The i.r. spectrum for dichloromethane solution shows an absorption band at 1 670 cm^–1, not present in that of the amide base, and assigned to ν(C–N). The u.v. spectrum for dichloromethane solution shows two weak absorption bands at 360 and 315 nm, whereas in aqueous solution there is only a single weak absorption band at 330 nm. Upon acidification of the aqueous solution, the u.v. spectrum of the protonated amide became identical with that obtained for dichloromethane solution.