  We present observations of 25 transitions of 17 isotopologues of 9 molecules
toward B335. With a goal of constraining chemical models of collapsing clouds,
we compare our observations, along with data from the literature, to models of
chemical abundances. The observed lines are simulated with a Monte Carlo code,
which uses various physical models of density and velocity as a function of
radius. The dust temperature as a function of radius is calculated
self-consistently by a radiative transfer code. The gas temperature is then
calculated at each radius, including gas-dust collisions, cosmic rays,
photoelectric heating, and molecular cooling. The results provide the input to
the Monte Carlo code. We consider both {\it ad hoc} step function models for
chemical abundances and abundances taken from a self-consistent modeling of the
evolution of a star-forming core. The step function models can match the
observed lines reasonably well, but they require very unlikely combinations of
radial variations in chemical abundances. Among the self-consistent chemical
models, the observed lines are matched best by models with somewhat enhanced
cosmic-ray ionization rates and sulfur abundances. We discuss briefly the steps
needed to close the loop on the modeling of dust and gas, including off-center
spectra of molecular lines.
