Hexamethylbenzene II (C$_{12}$H$_{18}$) Structure: A_aP12_2_6i-001
| Prototype | C$_{2}$H$_{3}$ |
| AFLOW prototype label | A_aP12_2_6i-001 |
| Mineral name | hexamethylbenzene |
| CCDC | 1176976 |
| Pearson symbol | aP12 |
| Space group number | 2 |
| Space group symbol | $P\overline{1}$ |
| AFLOW prototype command |
aflow --proto=A_aP12_2_6i-001
--params=$a, \allowbreak b/a, \allowbreak c/a, \allowbreak \alpha, \allowbreak \beta, \allowbreak \gamma, \allowbreak x_{1}, \allowbreak y_{1}, \allowbreak z_{1}, \allowbreak x_{2}, \allowbreak y_{2}, \allowbreak z_{2}, \allowbreak x_{3}, \allowbreak y_{3}, \allowbreak z_{3}, \allowbreak x_{4}, \allowbreak y_{4}, \allowbreak z_{4}, \allowbreak x_{5}, \allowbreak y_{5}, \allowbreak z_{5}, \allowbreak x_{6}, \allowbreak y_{6}, \allowbreak z_{6}$ |
- Solid hexamethylbenzene is found in three forms (Woodruff, 1977):
- Phase I (Watanabe, 1949) a triclinic high-temperature phase.
- Phase II (Brockway, 1939) is also triclinic, and is the room temperature phase.
- Phase III (Woodruff, 1977) is trigonal and stable below 115K.
- All three structures can be considered as a benzene ring with the hydrogen atoms replaced by methyl (CH$_{3}$) groups.
- Unfortunately we have not been able to obtain a copy of (Watanabe, 1949), and (Woodruff, 1977) only has Raman data and therefore cannot completely describe the structure of Phase III.
- (Lonsdale, 1928-1929) studied hexamethylbenzene as a means of understanding the crystal structure of benzene, which is liquid at room temperature. She determined that the carbon atoms were all co-planar, and by inference extended this finding to benzene. (Brockway, 1939) presented a refinement of the structure, and we use their results here.
- Each of the outer carbon atoms is connected to three hydrogen atoms, but those positions were never determined in either paper. We do not even know if they are organized to maintain the inversion symmetry of the $P\overline{1}$ #2 space group, or if the inversion is lost and the space group becomes $P1$ #1.
- The CCSD CIF file has no atomic positions.
\[ \begin{array}{ccc}
\mathbf{a_{1}}&=&a \,\mathbf{\hat{x}}\\\mathbf{a_{2}}&=&b \cos{\gamma} \,\mathbf{\hat{x}}+b \sin{\gamma} \,\mathbf{\hat{y}}\\\mathbf{a_{3}}&=&c_{x} \,\mathbf{\hat{x}}+c_{y} \,\mathbf{\hat{y}}+c_{z} \,\mathbf{\hat{z}}\\c_{x} & = & c \cos{\beta} \\ c_{y} & = & c (\cos{\alpha} - \cos{\beta}\cos{\gamma}) / {\sin{\gamma}} \\ c_{z} & = & \sqrt{c^2 - c_{x}^2- c_{y}^2}
\end{array}\]
Basis vectors
| Lattice coordinates | Cartesian coordinates | Wyckoff position | Atom type | |||
|---|---|---|---|---|---|---|
| $\mathbf{B_{1}}$ | = | $x_{1} \, \mathbf{a}_{1}+y_{1} \, \mathbf{a}_{2}+z_{1} \, \mathbf{a}_{3}$ | = | $\left(a x_{1} + b y_{1} \cos{\gamma} + c_{x} z_{1}\right) \,\mathbf{\hat{x}}+\left(b y_{1} \sin{\gamma} + c_{y} z_{1}\right) \,\mathbf{\hat{y}}+c_{z} z_{1} \,\mathbf{\hat{z}}$ | (2i) | C I |
| $\mathbf{B_{2}}$ | = | $- x_{1} \, \mathbf{a}_{1}- y_{1} \, \mathbf{a}_{2}- z_{1} \, \mathbf{a}_{3}$ | = | $- \left(a x_{1} + b y_{1} \cos{\gamma} + c_{x} z_{1}\right) \,\mathbf{\hat{x}}- \left(b y_{1} \sin{\gamma} + c_{y} z_{1}\right) \,\mathbf{\hat{y}}- c_{z} z_{1} \,\mathbf{\hat{z}}$ | (2i) | C I |
| $\mathbf{B_{3}}$ | = | $x_{2} \, \mathbf{a}_{1}+y_{2} \, \mathbf{a}_{2}+z_{2} \, \mathbf{a}_{3}$ | = | $\left(a x_{2} + b y_{2} \cos{\gamma} + c_{x} z_{2}\right) \,\mathbf{\hat{x}}+\left(b y_{2} \sin{\gamma} + c_{y} z_{2}\right) \,\mathbf{\hat{y}}+c_{z} z_{2} \,\mathbf{\hat{z}}$ | (2i) | C II |
| $\mathbf{B_{4}}$ | = | $- x_{2} \, \mathbf{a}_{1}- y_{2} \, \mathbf{a}_{2}- z_{2} \, \mathbf{a}_{3}$ | = | $- \left(a x_{2} + b y_{2} \cos{\gamma} + c_{x} z_{2}\right) \,\mathbf{\hat{x}}- \left(b y_{2} \sin{\gamma} + c_{y} z_{2}\right) \,\mathbf{\hat{y}}- c_{z} z_{2} \,\mathbf{\hat{z}}$ | (2i) | C II |
| $\mathbf{B_{5}}$ | = | $x_{3} \, \mathbf{a}_{1}+y_{3} \, \mathbf{a}_{2}+z_{3} \, \mathbf{a}_{3}$ | = | $\left(a x_{3} + b y_{3} \cos{\gamma} + c_{x} z_{3}\right) \,\mathbf{\hat{x}}+\left(b y_{3} \sin{\gamma} + c_{y} z_{3}\right) \,\mathbf{\hat{y}}+c_{z} z_{3} \,\mathbf{\hat{z}}$ | (2i) | C III |
| $\mathbf{B_{6}}$ | = | $- x_{3} \, \mathbf{a}_{1}- y_{3} \, \mathbf{a}_{2}- z_{3} \, \mathbf{a}_{3}$ | = | $- \left(a x_{3} + b y_{3} \cos{\gamma} + c_{x} z_{3}\right) \,\mathbf{\hat{x}}- \left(b y_{3} \sin{\gamma} + c_{y} z_{3}\right) \,\mathbf{\hat{y}}- c_{z} z_{3} \,\mathbf{\hat{z}}$ | (2i) | C III |
| $\mathbf{B_{7}}$ | = | $x_{4} \, \mathbf{a}_{1}+y_{4} \, \mathbf{a}_{2}+z_{4} \, \mathbf{a}_{3}$ | = | $\left(a x_{4} + b y_{4} \cos{\gamma} + c_{x} z_{4}\right) \,\mathbf{\hat{x}}+\left(b y_{4} \sin{\gamma} + c_{y} z_{4}\right) \,\mathbf{\hat{y}}+c_{z} z_{4} \,\mathbf{\hat{z}}$ | (2i) | C IV |
| $\mathbf{B_{8}}$ | = | $- x_{4} \, \mathbf{a}_{1}- y_{4} \, \mathbf{a}_{2}- z_{4} \, \mathbf{a}_{3}$ | = | $- \left(a x_{4} + b y_{4} \cos{\gamma} + c_{x} z_{4}\right) \,\mathbf{\hat{x}}- \left(b y_{4} \sin{\gamma} + c_{y} z_{4}\right) \,\mathbf{\hat{y}}- c_{z} z_{4} \,\mathbf{\hat{z}}$ | (2i) | C IV |
| $\mathbf{B_{9}}$ | = | $x_{5} \, \mathbf{a}_{1}+y_{5} \, \mathbf{a}_{2}+z_{5} \, \mathbf{a}_{3}$ | = | $\left(a x_{5} + b y_{5} \cos{\gamma} + c_{x} z_{5}\right) \,\mathbf{\hat{x}}+\left(b y_{5} \sin{\gamma} + c_{y} z_{5}\right) \,\mathbf{\hat{y}}+c_{z} z_{5} \,\mathbf{\hat{z}}$ | (2i) | C V |
| $\mathbf{B_{10}}$ | = | $- x_{5} \, \mathbf{a}_{1}- y_{5} \, \mathbf{a}_{2}- z_{5} \, \mathbf{a}_{3}$ | = | $- \left(a x_{5} + b y_{5} \cos{\gamma} + c_{x} z_{5}\right) \,\mathbf{\hat{x}}- \left(b y_{5} \sin{\gamma} + c_{y} z_{5}\right) \,\mathbf{\hat{y}}- c_{z} z_{5} \,\mathbf{\hat{z}}$ | (2i) | C V |
| $\mathbf{B_{11}}$ | = | $x_{6} \, \mathbf{a}_{1}+y_{6} \, \mathbf{a}_{2}+z_{6} \, \mathbf{a}_{3}$ | = | $\left(a x_{6} + b y_{6} \cos{\gamma} + c_{x} z_{6}\right) \,\mathbf{\hat{x}}+\left(b y_{6} \sin{\gamma} + c_{y} z_{6}\right) \,\mathbf{\hat{y}}+c_{z} z_{6} \,\mathbf{\hat{z}}$ | (2i) | C VI |
| $\mathbf{B_{12}}$ | = | $- x_{6} \, \mathbf{a}_{1}- y_{6} \, \mathbf{a}_{2}- z_{6} \, \mathbf{a}_{3}$ | = | $- \left(a x_{6} + b y_{6} \cos{\gamma} + c_{x} z_{6}\right) \,\mathbf{\hat{x}}- \left(b y_{6} \sin{\gamma} + c_{y} z_{6}\right) \,\mathbf{\hat{y}}- c_{z} z_{6} \,\mathbf{\hat{z}}$ | (2i) | C VI |
References
- L. O. Brockway and J. M. Robertson, The crystal structure of hexamethylbenzene and the length of the methyl group bond to aromatic carbon atoms, J. Chem. Soc. pp. 1324–1332 (1939), doi:10.1039/JR9390001324.
- K. Londsdale, The Structure of the Benzene Ring, Nature 122, 810 (1928), doi:10.1038/122810c0.
- K. Lonsdale, The Structure of the Benzene Ring in C$_{6}$(CH$_{3}$)$_{6}$, Proc. R. Soc. A 123, 494–515 (1929), doi:10.1098/rspa.1929.0081.
- S. D. Woodtruff and R. Kopelman, Phase III crystal structure and 115 K phase transition of hexamethylbenzene, J. Cryst. Mol. Struc. 7, 29–40 (1977), doi:10.1007/BF01239675.
- T. Watanabe, Y. Saito, and H. Chihra, , Sci. Papers Osaka Univ. 1, 9 (1949).
Prototype Generator
aflow --proto=A_aP12_2_6i --params=$a,b/a,c/a,\alpha,\beta,\gamma,x_{1},y_{1},z_{1},x_{2},y_{2},z_{2},x_{3},y_{3},z_{3},x_{4},y_{4},z_{4},x_{5},y_{5},z_{5},x_{6},y_{6},z_{6}$