  The formation pathways of different types of organic molecules in
protostellar envelopes and other regions of star formation are subjects of
intense current interest. We here present observations of C$_4$H and CH$_3$OH,
tracing two distinct groups of interstellar organic molecules, toward 16
protostars in the Ophiuchus and Corona Australis molecular clouds. Together
with observations in the literature, we present C$_4$H and CH$_3$OH data from
single-dish observations of 40 embedded protostars. We find no correlation
between the C$_4$H and CH$_3$OH column densities in this large sample. Based on
this lack of correlation, a difference in line profiles between C$_4$H and
CH$_3$OH, and previous interferometric observations of similar sources, we
propose that the emission from these two molecules is spatially separated, with
the CH$_3$OH tracing gas that has been transiently heated to high ($\sim$70-100
K) temperatures, and the C$_4$H tracing the cooler large-scale envelope where
CH$_4$ molecules have been liberated from ices. These results provide insight
in the differentiation between hot corino and warm carbon-chain chemistry in
embedded protostars.
