Two or more @M03986@ are described as isoelectronic if they have the same number of @V06588@ electrons and the same structure, i.e. number and @C01274@ of atoms, but differ in some of the elements involved. Thus: CO, N2 and NO+ are isoelectronic. CH2=C=O and CH2=N=N are isoelectronic. CH3COCH3 and CH3N=NCH3 have the same number of electrons, but have different structures, hence they are not described as isoelectronic.
PAC, 1994, 66, 1077. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1128 [Terms] [Paper]