### Abstract

Twistane, C_{10}H_{16}, is a classic D_{2}- symmetric chiral hydrocarbon that has been studied for decades due to its fascinating stereochemical and thermodynamic properties. Here we propose and analyze in detail the contiguous linear extension of twistane with ethano (ethane-1,2-diyl) bridges to create a new chiral, C_{2}-symmetric hydrocarbon nanotube called polytwistane. Polytwistane, (CH)_{n}, has the same molecular formula as polyacetylene but is composed purely of C(sp ^{3})ï£¿H units, all of which are chemically equivalent. The polytwistane nanotube has the smallest inner diameter (2.6 A) of hydrocarbons considered to date. A rigorous topological analysis of idealized polytwistane and a C_{236}H_{242} prototype optimized by B3LYP density functional theory reveals that the polymer has a nonrepeating, alternating σ-helix, with an irrational periodicity parameter and an instantaneous rise (or lead) angle near 15 °. A theoretical analysis utilizing homodesmotic equations and explicit computations as high as CCSD(T)/cc-pVQZ yields the enthalpies of formation {{\rm{\Delta }}-f H-0^ \circ }(twistane)=-1.7 kcal mol^{-1} and {{\rm{\Delta }}-f H-0^ \circ }(polytwistane)= +1.28 kcal (mol CH)^{-1}, demonstrating that the hypothetical formation of polytwistane from acetylene is highly exothermic. Hence, polytwistane is synthetically viable both on thermodynamic grounds and also because no obvious pathways exist for its rearrangement to lower-lying isomers. The present analysis should facilitate the preparation and characterization of this new chiral hydrocarbon nanotube. Let's do the twist: Polytwistane is an experimentally unrealized (CH)_{n} alkane exhibiting helical chirality and a regular carbon nanotube. A rigorous theoretical analysis of its topology reveals that polytwistane contains a non-repeating, alternating primary helix stiffened by longitudinal crosslinks (see figure). Thermochemical computations suggest that polytwistane is a viable synthetic target.

Original language | English (US) |
---|---|

Pages (from-to) | 1638-1645 |

Number of pages | 8 |

Journal | Chemistry - A European Journal |

Volume | 20 |

Issue number | 6 |

DOIs | |

State | Published - Feb 3 2014 |

### Fingerprint

### Keywords

- alkanes
- chirality
- density functional calculations
- nanotubes
- stereochemistry
- thermodynamics

### ASJC Scopus subject areas

- Chemistry(all)

### Cite this

*Chemistry - A European Journal*,

*20*(6), 1638-1645. https://doi.org/10.1002/chem.201303081

**Polytwistane.** / Barua, Shiblee R.; Quanz, Henrik; Olbrich, Martin; Schreiner, Peter R.; Trauner, Dirk; Allen, Wesley D.

Research output: Contribution to journal › Article

*Chemistry - A European Journal*, vol. 20, no. 6, pp. 1638-1645. https://doi.org/10.1002/chem.201303081

}

TY - JOUR

T1 - Polytwistane

AU - Barua, Shiblee R.

AU - Quanz, Henrik

AU - Olbrich, Martin

AU - Schreiner, Peter R.

AU - Trauner, Dirk

AU - Allen, Wesley D.

PY - 2014/2/3

Y1 - 2014/2/3

N2 - Twistane, C10H16, is a classic D2- symmetric chiral hydrocarbon that has been studied for decades due to its fascinating stereochemical and thermodynamic properties. Here we propose and analyze in detail the contiguous linear extension of twistane with ethano (ethane-1,2-diyl) bridges to create a new chiral, C2-symmetric hydrocarbon nanotube called polytwistane. Polytwistane, (CH)n, has the same molecular formula as polyacetylene but is composed purely of C(sp 3)ï£¿H units, all of which are chemically equivalent. The polytwistane nanotube has the smallest inner diameter (2.6 A) of hydrocarbons considered to date. A rigorous topological analysis of idealized polytwistane and a C236H242 prototype optimized by B3LYP density functional theory reveals that the polymer has a nonrepeating, alternating σ-helix, with an irrational periodicity parameter and an instantaneous rise (or lead) angle near 15 °. A theoretical analysis utilizing homodesmotic equations and explicit computations as high as CCSD(T)/cc-pVQZ yields the enthalpies of formation {{\rm{\Delta }}-f H-0^ \circ }(twistane)=-1.7 kcal mol-1 and {{\rm{\Delta }}-f H-0^ \circ }(polytwistane)= +1.28 kcal (mol CH)-1, demonstrating that the hypothetical formation of polytwistane from acetylene is highly exothermic. Hence, polytwistane is synthetically viable both on thermodynamic grounds and also because no obvious pathways exist for its rearrangement to lower-lying isomers. The present analysis should facilitate the preparation and characterization of this new chiral hydrocarbon nanotube. Let's do the twist: Polytwistane is an experimentally unrealized (CH)n alkane exhibiting helical chirality and a regular carbon nanotube. A rigorous theoretical analysis of its topology reveals that polytwistane contains a non-repeating, alternating primary helix stiffened by longitudinal crosslinks (see figure). Thermochemical computations suggest that polytwistane is a viable synthetic target.

AB - Twistane, C10H16, is a classic D2- symmetric chiral hydrocarbon that has been studied for decades due to its fascinating stereochemical and thermodynamic properties. Here we propose and analyze in detail the contiguous linear extension of twistane with ethano (ethane-1,2-diyl) bridges to create a new chiral, C2-symmetric hydrocarbon nanotube called polytwistane. Polytwistane, (CH)n, has the same molecular formula as polyacetylene but is composed purely of C(sp 3)ï£¿H units, all of which are chemically equivalent. The polytwistane nanotube has the smallest inner diameter (2.6 A) of hydrocarbons considered to date. A rigorous topological analysis of idealized polytwistane and a C236H242 prototype optimized by B3LYP density functional theory reveals that the polymer has a nonrepeating, alternating σ-helix, with an irrational periodicity parameter and an instantaneous rise (or lead) angle near 15 °. A theoretical analysis utilizing homodesmotic equations and explicit computations as high as CCSD(T)/cc-pVQZ yields the enthalpies of formation {{\rm{\Delta }}-f H-0^ \circ }(twistane)=-1.7 kcal mol-1 and {{\rm{\Delta }}-f H-0^ \circ }(polytwistane)= +1.28 kcal (mol CH)-1, demonstrating that the hypothetical formation of polytwistane from acetylene is highly exothermic. Hence, polytwistane is synthetically viable both on thermodynamic grounds and also because no obvious pathways exist for its rearrangement to lower-lying isomers. The present analysis should facilitate the preparation and characterization of this new chiral hydrocarbon nanotube. Let's do the twist: Polytwistane is an experimentally unrealized (CH)n alkane exhibiting helical chirality and a regular carbon nanotube. A rigorous theoretical analysis of its topology reveals that polytwistane contains a non-repeating, alternating primary helix stiffened by longitudinal crosslinks (see figure). Thermochemical computations suggest that polytwistane is a viable synthetic target.

KW - alkanes

KW - chirality

KW - density functional calculations

KW - nanotubes

KW - stereochemistry

KW - thermodynamics

UR - http://www.scopus.com/inward/record.url?scp=84895059481&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84895059481&partnerID=8YFLogxK

U2 - 10.1002/chem.201303081

DO - 10.1002/chem.201303081

M3 - Article

VL - 20

SP - 1638

EP - 1645

JO - Chemistry - A European Journal

JF - Chemistry - A European Journal

SN - 0947-6539

IS - 6

ER -