Geometric isomerism in polyacetylene is ab asic concept in chemistry textbooks.Polymerization to cis-isomer is kinetically preferred at lowtemperature,not only in the classic catalytic reaction in solution but also,u nexpectedly,i nt he crystalline phase when it is driven by external pressure without ac atalyst. Until now,n op erfect reaction route has been proposed for this pressure-induced polymerization. Using in situ neutron diffraction and meta-dynamic simulation, we discovered that under high pressure,acetylene molecules react along aspecific crystallographic direction that is perpendicular to those previously proposed. Following this route produces apure cis-isomer and more surprisingly,predicts that graphane is the final product. Experimentally,p olycyclic polymers with alayered structure were identified in the recovered product by solid-state nuclear magnetic resonance and neutron pair distribution functions,w hich indicates the possibility of synthesizing graphane under high pressure.

Pressure-induced polymerization (PIP) of aromatics is anovel method for constructing sp 3 -carbon frameworks, and nanothreads with diamond-like structures were synthesized by compressing benzene and its derivatives.H ere by compressing abenzene-hexafluorobenzene cocrystal (CHCF), H-F-substituted graphane with al ayered structure in the PIP product was identified. Based on the crystal structure determined from the in situ neutron diffraction and the intermediate products identified by gas chromatography-mass spectrum, we found that at 20 GPaCHCF forms tilted columns with benzene and hexafluorobenzene stackeda lternatively,a nd leads to a[4+ +2] polymer,which then transforms to short-range ordered H-F-substituted graphane.The reaction process involves [4+ +2] Diels-Alder,r etro-Diels-Alder,a nd 1-1' coupling reactions, and the former is the key reaction in the PIP.T hese studies confirm the elemental reactions of PIP of CHCF for the first time,and provide insight into the PIP of aromatics.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.