Methanimine (CH₂NH) was initially detected in Sgr B2 by Godfrey et al. and reported in 1973. As summarized by Müller, it has been found in other hot core sources, and its ¹³C isotope has also been identified, by Cummins et al. Methanimine was recently detected in the ultraluminous infrared galaxy (ULIRG) Arp 200 by Salter et al. with the Arecibo radio telescope, a discovery that is particularly remarkable because this object is 250 million light years away. In addition to the vast distance, methanimine is of interest because it is an amino acid precursor.

Methanime (also known as methyleneimine) is isolectronic with formaldehyde. Like O in the latter, the -NH imine group forms a double bond with the triplet methylene.