NH2-CO-NH2 Now replace one hydrogen with CH3. You get methylurea: CH3NH-CO-NH2 It looks like a tiny change. But something important has happened. Urea is symmetrical. Methylurea isn't.
Its two nitrogen atoms are now chemically different. That makes methylurea useful when chemists want to build unsymmetrical urea-containing molecules or nitrogen heterocycles with one methyl group already in the right place.
Global Chemical Database