Linearly Polymerized Benzene Arrays As Intermediates, Tracing Pathways to Carbon Nanothreads

How might fully saturated benzene
polymers of composition [(CH)6]n form under high pressure? In
the first approach to answering this question, we examine the stepwise
increase in saturation of a one-dimensional stack of benzene molecules
by enumerating the partially saturated polymer intermediates, subject
to constraints of unit cell size and energy. Defining the number of
four-coordinate carbon atoms per benzene formula unit as the degree
of saturation, a set of isomers for degree-two and degree-four polymers
can be generated by either thinking of the propagation of partially
saturated building blocks or by considering a sequence of cycloadditions.
There is also one 4 + 2 reaction sequence that jumps directly from
a benzene stack to a degree-four polymer. The set of degree-two polymers
provides several useful signposts toward achieving full saturation:
chiral versus achiral building blocks, certain forms of conformational
freedom, and also dead ends to further saturation. These insights
allow us to generate a larger set of degree-four polymers and enumerate
the many pathways that lead from benzene stacks to completely saturated
carbon nanothreads.