Construction of vitrinite molecular structures based on 13C NMR and FT-IR analysis: Fundamental insight into coal thermoplastic properties

•Chemical structures of vitrinite were investigated by characterization techniques.•Molecular structure models of vitrinite were established.•Correlation between vitrinite structure and thermoplastic properties were studied.•Cyclic aliphatic structures contribute significantly to fluidity.•Aromatic rings may originate from cyclic aliphatic structures.