  The chemical composition of high-mass protostars reflects the physical
evolution associated with different stages of star formation. In this study,
the molecular inventory of the forming high-mass star AFGL 4176 is studied in
detail at high angular resolution (~0.35 arcsec) using ALMA. This high
resolution makes it possible to separate the emission associated with the inner
hot envelope and disk around the forming star from that of its cool outer
envelope. In addition, the high sensitivity of ALMA makes it possible to
identify weak and optically thin lines and allows for many isotopologues to be
detected, providing a more complete and accurate inventory of the source. A
total of 23 different molecular species and their isotopologues are detected in
the spectrum towards AFGL 4176. The most abundant species is methanol (CH3OH),
remaining species are present at levels between 0.003 % and 15 % with respect
to CH3OH. Hints that N-bearing species peak slightly closer to the location of
the peak continuum emission than the O-bearing species are seen. AFGL 4176
comprises a rich chemical inventory including many complex species present on
disk-scales. On average, the derived column density ratios with respect to
methanol of O-bearing species are higher than those derived for N-bearing
species by a factor of three. This may indicate that AFGL 4176 is a relatively
young source since nitrogen chemistry generally takes longer to evolve in the
gas-phase. Taking methanol as a reference, the composition of AFGL 4176 more
closely resembles that of the low-mass protostar IRAS 16293-2422B than that of
high-mass star-forming regions located near the Galactic centre. This
similarity hints that the chemical composition of complex species is already
set in the cold cloud stage and implies that AFGL 4176 is a young source whose
chemical composition has not yet been strongly processed by the central
protostar.
