Prismanes
The prismanes are a class of hydrocarbon compounds consisting of prism-like polyhedra of various numbers of sides on the polygonal base. Chemically, it is a series of fused cyclobutane rings (a ladderane, with all-cis/all-syn geometry) that wraps around to join its ends and form a band, with cycloalkane edges. Their chemical formula is (C2H2)n, where n is the number of cyclobutane sides (the size of the cycloalkane base), and that number also forms the basis for a system of nomenclature within this class. The first few chemicals in this class are:
| Structures |  |
 |
 |
 |
|---|---|---|---|---|
| Common name | Prismane [3]Prismane Triprismane |
Cubane (preferred) [4]Prismane Tetraprismane |
[5]Prismane Pentaprismane |
[6]Prismane Hexaprismane |
| Chemical formula | (C2H2)3 C6H6 |
(C2H2)4 C8H8 |
(C2H2)5 C10H10 |
(C2H2)6 C12H12 |
| IUPAC nomenclature | tetracyclo |
pentacyclo |
hexacyclo |
heptacyclo |
| 3D models (PubChem) | triprismane | cubane | pentaprismane | hexaprismane |
Triprismane, tetraprismane, and pentaprismane have been synthesized and studied experimentally. As of 1994[update], hexaprismane and higher members have not been successfully synthesized.[1]
The geometries of the unknown members have been studied using computer models. Initially, they do have the geometry of a regular prism, with flat n-gon bases. As n becomes increasingly large, however, the highly symmetric geometry is expected to be unfavorable, with the molecule distorting into less-symmetric forms. One series of models suggests that the transition occurs at [11]prismane. For example, the structure of [12]prismane would have the cyclobutane chain twisted, with the dodecagonal bases non-planar and non-parallel.[2][3] [4]
Hexaprismane and octaprismane are expected to be kinetically stable.[5]
The prismanes have also been studied in terms of the aromatic or antiaromatic nature of the cage.[6] Hexaprismane in particular would not be thermodynamically stable because it is the dimer of highly stable benzene.
Nonconvex prismanes
[edit]
For large base-sizes, some of the cyclobutanes can be fused anti to each other, giving a non-convex polygon base. These are geometric isomers of the prismanes. Two isomers of [12]prismane that have been studied computationally are named helvetane and israelane, based on the star-like shapes of the rings that form their bases.[7] This was explored computationally after originally being proposed as an April fools joke. Their names refer to the shapes found on the flags of Switzerland and Israel, respectively.
Polyprismanes
[edit]
The polyprismanes consist of multiple prismanes stacked base-to-base.[8] The carbons at each intermediate level—the n-gon bases where the prismanes fuse to each other—have no hydrogen atoms attached to them.
Related structures
[edit]
The asteranes contain a methylene group bridge on each edge between the two n-gon bases. Each side is thus a cyclohexane rather than a cyclobutane.
A substituted compound based on hexasilaprismane, the all-silicon analog of triprismane, has been synthesized.[9] Theoretical analysis suggests that the prismane form of Si6H6 is more stable than the aromatic-ring or Dewar benzene-like isomers of Si6H6.[10][11]
References
[edit]- ↑ Forman, Mark A.; Dailey, William P. (1994). "The synthesis and reactions of prismanes". Organic Preparations and Procedures International. 26 (3). Taylor & Francis. doi:10.1080/00304949409458427.
- ↑ Gribanova, T. N.; Minyaev, R. M.; Minkin, V. I. (2007). "Quantum-chemical investigation of structure and stability of [n]-prismanes and [n]-asteranes". Russian Journal of Organic Chemistry. 43 (8): 1144–1150. doi:10.1134/S107042800708009X. S2CID 97458519.
- ↑ Shinmyozu, Terou; Nogita, Riki; Akita, Motoki; Lim, Chultack (2003). "23. Photochemical Approaches to the Synthesis of [n]Prismanes". In Horspool, William H.; Lenci, Francesco (eds.). CRC Handbook of Organic Photochemistry and Photobiology, Volumes 1 & 2, Second Edition. CRC Press. ISBN 9780203495902.
- ↑ Allinger, Norman L.; Eaton, Philip E. (1983). "The geometries of pentaprismane and hexaprismane insights from molecular mechanics". Tetrahedron Letters. 24 (35): 3697–3700. doi:10.1016/S0040-4039(00)94512-X.
- ↑ Shostachenko, S. A.; Maslov, M. M.; Prudkovskii, V. S.; Katin, K. P. (2015). "Thermal stability of hexaprismane C12H12 and octaprismane C16H16". Physics of the Solid State. 57 (5): 1023–1027. doi:10.1134/S1063783415050261.
- ↑ Alonso, Mercedes; Poater, Jordi; Solà, Miquel (2007). "Aromaticity changes along the reaction coordinate connecting the cyclobutadiene dimer to cubane and the benzene dimer to hexaprismane". Structural Chemistry. 18 (6): 773–783. doi:10.1007/s11224-007-9240-4.
- ↑ Wang, Xin; Lau, Kai-Chung; Li, Wai-Kee (2009). "Structures and Properties of Closed Ladderanes C24H24, Laddersilanes Si24H24, and Their Nitrogen-Containing Isoelectronic Equivalents: A G3(MP2) Investigation". J. Phys. Chem. A. 113 (14): 3413–3419. Bibcode:2009JPCA..113.3413W. doi:10.1021/jp900161s. PMID 19296633.
- ↑ Minyaev, Ruslan M.; Minkin, Vladimir I.; Gribanova, Tatyana N.; Starikov, Andrey G.; Hoffmann, Roald (2003). "Poly[n]prismanes: A Family of Stable Cage Structures with Half-Planar Carbon Centers". J. Org. Chem. 68 (22): 8588–8594. doi:10.1021/jo034910l. PMID 14575490.
- ↑ Sekiguchi, A.; Yatabe, T.; Kabuto, C.; Sakurai, H. (1993). "Chemistry of Organosilicon Compounds. 303. The "Missing" Hexasilaprismane: Synthesis, X-Ray Analysis and Photochemical Reactions". Journal of the American Chemical Society. 115 (13): 5853–5854. doi:10.1021/ja00066a075.
- ↑ Sax, Alexander; Janoschek, Rudolf (1986). "Si6H6: Is the Aromatic Structure the Most Stable One?". Angewandte Chemie International Edition in English. 25 (7): 651–652. doi:10.1002/anie.198606511.
- ↑ Janoschek, R. (1995). "Si6H6 revisited: The hexasilaprismane-to-hexasilabenzene and hexasila-dewarbenzene interconversion". Journal of Inorganic and Organometallic Polymers. 5 (2): 155–161. doi:10.1007/BF01058143.