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

Abstract

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: Addition and Condensation Reactions

“…We also predicted a series of lithium polycarbides with a stoichiometric ratio of Li n+1 C 2n (Figure 3c), which share the common feature of zigzag nano-ribbon structure with various width, and LiC 2 (n = ∞) and Li 3 C 4 (n = 2) are the two terminal compounds (Figure 3b) [33]. As mentioned, acetylene normally reacts at around 5.0 GPa [23], while the polymerization pressures of disubstituted metal acetylides are mostly over 20 GPa (~22 GPa for CaC2, and 35 GPa for Li2C2 [31,32]) due to the repulsion of the electrostatic interaction and spatial blocking of the cations. We also studied the monosubstituted acetylene sodium As mentioned, acetylene normally reacts at around 5.0 GPa [23], while the polymerization pressures of disubstituted metal acetylides are mostly over 20 GPa (~22 GPa for CaC 2 , and 35 GPa for Li 2 C 2 [31,32]) due to the repulsion of the electrostatic interaction and spatial blocking of the cations.…”

“…As mentioned, acetylene normally reacts at around 5.0 GPa [23], while the polymerization pressures of disubstituted metal acetylides are mostly over 20 GPa (~22 GPa for CaC2, and 35 GPa for Li2C2 [31,32]) due to the repulsion of the electrostatic interaction and spatial blocking of the cations. We also studied the monosubstituted acetylene sodium As mentioned, acetylene normally reacts at around 5.0 GPa [23], while the polymerization pressures of disubstituted metal acetylides are mostly over 20 GPa (~22 GPa for CaC 2 , and 35 GPa for Li 2 C 2 [31,32]) due to the repulsion of the electrostatic interaction and spatial blocking of the cations. We also studied the monosubstituted acetylene sodium (NaC 2 H) with only one charge on the carbon group [34].…”

“…We used Paris-Edinburgh Press (PE press) as a HP generation apparatus to avoid the photoactivation and facilitates the in situ neutron diffraction [20][21][22]. The crystal structure of deuterated acetylene at the critical reaction pressure of 5.7 GPa was determined by in situ neutron diffraction, from which we found the possible reaction route to produce cis-PA [23]. As shown Figure 1a (left), the previous proposed bonding route along a+b or a−b direction will result in trans-PA (grey line route) [17,18], while there is another bonding route along the a+c and a−c direction with D C of 3.1 Å (yellow line), which will promote the formation of cis-polymer.…”

Nanoarchitecture through Strained Molecules: Cubane-Derived Scaffolds and the Smallest Carbon Nanothreads

“…It is also important to compare the experimental results with other possible CH polymorphs. Several CH structures have been proposed to be thermodynamically stable or metastable and could potentially be obtained from the compression of small CH molecules. , For example, several proposed graphane structures exhibit volumes from 11.12 to 13.65 Å 3 /CH depending on stacking geometry . Benzene polymer II possesses a volume of 12.8 Å 3 /CH, and the hypothetical 3D polymorphs K 4 -CH, hex-CH, and R 6 -CH all have volumes near 9.65 Å 3 /CH.…”

Pressure-driven electronic phase transition in the high-pressure phase of nitrogen-rich 1H-tetrazoles

“…Some unsaturated organic molecules tend to form a more saturated polymer with an extended structure and higher density under pressure. [9][10][11] For instance, several structures of polymeric nitrogen have been predicted to exist under extreme high-pressure conditions, such as cubic-gauche (cg-N), and layered (LP-N) polymeric nitrogen. [12][13][14][15][16] Polymeric nitrogen, a pure single-bonded nitrogen compound, has attracted much interest because of the signicant difference between the single bond ($160 kJ mol À1 ) and triple bond ($946 kJ mol À1 ).…”