  Molecular complexity builds up at each step of the Sun-like star formation
process, starting from simple molecules and ending up in large polyatomic
species. Complex organic molecules (COMs; such as methyl formate, HCOOCH$_3$,
dymethyl ether, CH$_3$OCH$_3$, formamide, NH$_2$CHO, or glycoaldehyde,
HCOCH$_2$OH) are formed in all the components of the star formation recipe
(e.g. pre-stellar cores, hot-corinos, circumstellar disks, shocks induced by
fast jets), due to ice grain mantle sublimation or sputtering as well as
gas-phase reactions. Understanding in great detail the involved processes is
likely the only way to predict the ultimate molecular complexity reached in the
ISM, as the detection of large molecules is increasingly more difficult with
the increase of the number of atoms constituting them.
  Thanks to the recent spectacular progress of astronomical observations, due
to the Herschel (sub-mm and IR), IRAM and SMA (mm and sub-mm), and NRAO (cm)
telescopes, an enormous activity is being developed in the field of
Astrochemistry, extending from astronomical observatories to chemical
laboratories. We are involved in several observational projects providing
unbiased spectral surveys (in the 80-300 and 500-2000 GHz ranges) with
unprecedented sensitivity of templates of dense cores and protostars. Forests
of COM lines have been detected. In this chapter we will focus on the chemistry
of both cold prestellar cores and hot shocked regions, (i) reviewing results
and open questions provided by mm-FIR observations, and (ii) showing the need
of carrying on the observations of COMs at lower frequencies, where SKA will
operate. We will also emphasize the importance of analysing the spectra by the
light of the experimental studies performed by our team, who is investigating
the chemical effects induced by ionising radiation bombarding astrophysically
relevant ices.
