  We have made self-consistent models of the density and temperature profiles
of the gas and dust surrounding embedded luminous objects using a detailed
radiative transfer model together with observations of the spectral energy
distribution of hot molecular cores. Using these profiles we have investigated
the hot core chemistry which results when grain mantles are evaporated, taking
into account the different binding energies of the mantle molecules, as well a
model in which we assume that all molecules are embedded in water ice and have
a common binding energy. We find that most of the resulting column densities
are consistent with those observed toward the hot core G34.3+0.15 at a time
around 10$^4$ years after central luminous star formation. We have also
investigated the dependence of the chemical structure on the density profile
which suggests an observational possibility of constraining density profiles
from determination of the source sizes of line emission from desorbed
molecules.
