Molecular manufacturing should let us synthesize most arrangements of
atoms that are consistent with physical law. Assemblers have been prop
osed as a means of accomplishing this objective. They would be able to
build a wide range of useful products as well as copies of themselves
. A simpler though less general proposal is a hydrocarbon assembler, r
estricted to manufacturing relatively stiff hydrocarbons. The design a
nd analysis of such an assembler should be substantially simpler than
that of a more general assembler. In this paper, we consider the 'inte
rmediary metabolism' of a hydrocarbon assembler, i.e. the set of react
ions that permit processing of the feedstock molecules and their conve
rsion into molecular tools (positionally controlled carbenes, radicals
, and other reactive species). The specific feedstock molecule analyze
d is butadiyne (a linear molecule, C4H2, also known as diacetylene; no
t to be confused with the more common but chemically distinct nonlinea
r molecule butadiene: C4H6).