Pressure‐Induced Polymerization of Acetylene: Structure‐Directed Stereoselectivity and a Possible Route to Graphane

Abstract

Geometric isomerism in polyacetylene is a basic concept in chemistry textbooks. Polymerization to cis-isomer is kinetically preferred at low temperature, not only in the classic catalytic reaction in solution but also, unexpectedly, in the crystalline phase when it is driven by external pressure without a catalyst. Until now, no perfect 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 a specific crystallographic direction that is perpendicular to those previously proposed. Following this route produces a pure cis-isomer and more surprisingly, predicts that graphane is the final product. Experimentally, polycyclic polymers with a layered structure were identified in the recovered product by solid-state nuclear magnetic resonance and neutron pair distribution functions, which indicates the possibility of synthesizing graphane under high pressure.

The Effect of Pressure on Organic Reactions in Fluids—a New Theoretical Perspective

“…[79,80] Another approach is that of molecular dynamics,w hether classical or quantum. [81][82][83][84][85][86] In this context, we wish to mention the works of the Houk, [87,88] Carpenter, [89] and Singleton [90] groups of using molecular dynamics to study molecular organic reactions at ambient pressure.…”

“…Similar idea has also been applied to compressing H 2 in one dimension . Another approach is that of molecular dynamics, whether classical or quantum . In this context, we wish to mention the works of the Houk, Carpenter, and Singleton groups of using molecular dynamics to study molecular organic reactions at ambient pressure.…”

From Molecules to Carbon Materials—High Pressure Induced Polymerization and Bonding Mechanisms of Unsaturated Compounds

“…Based on the calculated crystal structure of acetylene, the possible reaction route was proposed, but the selectivity of cis-polyacetylene could not be explained by the bonding route along the face diagonal of the a-b plane proposed in the literature [89][90][91][92][93]. By collecting the in situ high-pressure neutron diffraction data, the crystal structure (Figure 7a) at the threshold reaction pressure, 5.7 GPa, was determined [94]. Another reaction route along the face diagonal of the a−c plane is figured out, in which the C .…”

“…At 77 K, acetylene polymerizes at about 11 GPa, and mainly produces cis-polyacetylene [93], which isomerizes to the trans-isomer when warmed to room temperature. Based on the calculated crystal structure of acetylene, the possible reaction route was proposed, but the selectivity of cispolyacetylene could not be explained by the bonding route along the face diagonal of the a-b plane proposed in the literature [90][91][92][93][94]. By collecting the in situ high-pressure neutron diffraction data, the crystal structure (Figure 7a) at the threshold reaction pressure, 5.7 GPa, was determined [95].…”

Compression of glycolide-h4 to 6 GPa

“…There have been a number of spectroscopic studies (Murli & Song, 2010;Bini et al, 2012;Ceppatelli et al, 2000;Chelazzi et al, 2005;Ciabini et al, 2002;Ciabini et al, 2007;Santoro et al, 2003;Aoki et al, 1989;Kojima et al, 1995;Murli et al, 2012) but only a few diffraction-based studies (Jin et al, 2013;Wilhelm et al, 2008) that have investigated chemical reactions in a range of aromatic, olefinic materials. Recent work by Sun et al (2017) has highlighted the role of neutron powder diffraction and solid-state NMR to elucidate the pathways to various products from the compression of acetylene depending on the pressure achieved. Ring systems have been investigated using spectroscopy and observed to undergo chemical reactions, e.g.…”