  We combine {\em ab initio} density functional theory (DFT) structural studies
with DFT-based nonequilibrium Green function calculations to investigate how
the presence of non-hexagonal rings affects electronic transport in graphitic
structures. We find that infinite monolayers, finite-width nanoribbons and
nanotubes formed of 5-8 haeckelite with only 5- and 8-membered rings are
generally more conductive than their graphene-based counterparts. Presence of
haeckelite defect lines in the perfect graphitic structure, a model of grain
boundaries in CVD-grown graphene, increases the electronic conductivity and
renders it highly anisotropic.
