A molecule with a different set of isotopes in it. Some
isopotologues of C2H5OH are shown
below:
H H H H H D
| | | | | |
H-C-C-O-D D-C-C-O-D D-C-C-O-H
| | | | | |
H H H H D H
Isotopologues should not be confused with
isotopomers.
http://www.iupac.org/goldbook/I03351.pdf