Partial premixing within simple gas jet diffusion flames has a very long history - reaching back to the Bunsen flame. Yet HRTEM data of soot from such flames appears absent. Using benzene as the primary fuel with partial premixing tested the chemical path for C5 production - proceeding through partial benzene oxidation yielding the phenoxy radical followed by CO loss to produce C5. A strong variation of lamellae curvature with oxygen content in the primary fuel stream was observed - reflecting the increasing C5 production rate. Generality of the nanostructure dependence upon partial premixing and associated change in gas phase chemistry (compared to pure thermal pyrolysis) was demonstrated using an ordinary laboratory Bunsen burner with ethylene as fuel. Absent partial premixing, soot production is well described by the HACA mechanism, yielding benzenoid aromatics and soot nanostructure consisting of flat lamellae, without curvature, dissimilar to observations described here accompanying partial premixing. (C) 2016 Published by Elsevier Inc. on behalf of The Combustion Institute.