The tautimerization between a nitroalkane and an acinitroalkane is presented in the chemical literature to be important for primary and secondary mono-nitroalkanes. It has been reported that for nitroethane and nitromethane the acinitro tautomer is present in about 10%, a value higher than estimated for the enol/keto tautomerization of monoketones. These estimates are based upon a rapid titration of a nitroalkane sample with molecular bromine in a method similar to the determination of the amount of the enol tautomer present in ketones. We have reinvestigated this tautomerization for nitromethane by the method of 1HNMR spectroscopy and have found very low levels of the acinitroalkane in nitromethane. The method used and the results in water and buffered solutions will be presented.