  Remote observations of comets, especially using high spectral resolution
millimeter spectroscopy, have enabled the detection of over 25 molecules in
comets for the last twenty years. Among the molecules identified at radio
wavelengths, complex organic molecules (COMs) such as acetaldehyde,
ethylene-glycol, formamide, methyl-formate or ethanol have been observed in
several comets and their abundances relative to water and methanol precisely
determined. Significant upper limits on the abundance of several other COMs
have been determined and put constraints on the dominant isomer for three of
them. The abundances measured in comets are generally of comparable order of
magnitude as those measured in star-forming regions, suggesting that comets
contain preserved material from the presolar cloud from which the solar system
was born.
