  Hot molecular cores (HMCs) are intermediate stages of high-mass star
formation and are also known for their rich emission line spectra at (sub-)mm
wavebands. The observed spectral feature of HMCs such as total number of
emission lines and associated line intensities are also found to vary with
evolutionary stages. We developed various 3D models for HMCs guided by the
evolutionary scenarios proposed by recent empirical and modeling studies. We
then investigated the spatio-temporal variation of temperature and molecular
abundances in HMCs by consistently coupling gas-grain chemical evolution with
radiative transfer calculations. We explored the effects of varying physical
conditions on molecular abundances including density distribution and
luminosity evolution of the central protostar(s). The time-dependent
temperature structure of the hot core models provides a realistic framework for
investigating the spatial variation of ice mantle evaporation as a function of
evolutionary timescales. With increasing protostellar luminosity, the water ice
evaporation font ($\sim$100K) expands and the spatial distribution of gas phase
abundances of these COMs also spreads out. We simulated the synthetic spectra
for these models at different evolutionary timescales to compare with
observations. A qualitative comparison of the simulated and observed spectra
suggests that these self-consistent hot core models can reproduce the notable
trends in hot core spectral variation within the typical hot core timescales of
10$^{5}$ year. These models predict that the spatial distribution of various
emission line maps will also expand with evolutionary time. The model
predictions can be compared with high resolution observation that can probe
scales of a few thousand AU in high-mass star forming regions such as from
ALMA.[Abridged]
