The Molecular Zoo Entry for
Benzvalene (tricyclo[3.1.0.02,6]hex-3-ene)
Prepared by Dan
Hickstein –
Summary. Benzvalene is one of the classic isomers of benzene which include prismane, Dewar benzene, and Claus Benzene. It has a highly rigid structure and so other conformers are not a concern. The structure of the molecule has been determined by electron diffraction[1] in 1974 and microwave spectroscopy[2] in 1973. The microwave study established the C2v symmetry of the molecule. As a result of this symmetry, the protons belong into 3 pairs of identical, indistinguishable Fermions. The Pauli Exclusion Principle applies with consequences for the relative intensities in the microwave spectrum. A 2003 study[3], using quantum mechanical computational methods to estimate the vibrational frequencies and structure of benzvalene, selected the parameters from the microwave study as the experimental comparisons. This is suggestive that the structure derived from the microwave spectrum is more reliable than the structure calculated from the electron diffraction pattern. This conclusion is further supported by molecular mechanics, semi-empirical, and quantum mechanical calculations, which are in better agreement with the microwave structure than with the electron diffraction structure. Calculations using density functional theory B3LYP with the 6-31G* basis set find that the electron diffraction structure has an energy of -232.1064 Hartrees while the microwave structure has an energy of -232.1189 Hartrees, a difference of 7.86 Kcal/mol. The large energetic difference in the structures using a high level of theory strongly suggests that the structure generated from the microwave data is more reasonable.
Suenram and Harmony observed rotational constants for a number of different isotopomers of benzvalene as summarized in the table below. The numbers in the headings refer to which carbon or hydrogen was substituted. They correspond to the numbering scheme in the numbered molecule below.
The Structure Files
mol2 and pdb files are available for these structures:
1) The microwave structure of Suenram and Harmony (mol2 pdb)
2) The electron diffraction structure of Karl and Bauer (mol2 pdb)
The paper did not specify the angles of the carbon-hydrogen bonds. The angles from the microwave structure were used for this structure.
3) The equilibrium conformer using the Tripos (SYBYL) force field (mol2 pdb)
4) The equilibrium conformer using MMFF94 force field (mol2 pdb)
5) The equilibrium conformer using semi-empirical AM1 (mol2 pdb)
6) The equilibrium conformer using Hartree-Fock 3-21G* (mol2 pdb)
|
Method |
C1,C6 |
C1,C2 |
C2,C3 |
C3,C4 |
C1,H1 |
C2,H2 |
C3,H3 |
Angle(C3,C2,C6) |
|
Microwave |
1.4522 |
1.5323 |
1.4967 |
1.3394 |
1.0777 |
1.0844 |
1.0784 |
108.77 |
|
Electron Diffraction |
1.4404 |
1.5300 |
1.5034 |
1.3259 |
1.1408 |
1.1410 |
1.1379 |
111.07 |
|
Tripos Force Field |
1.5438 |
1.5371 |
1.5058 |
1.3428 |
1.1044 |
1.1002 |
1.0893 |
99.76 |
|
MMFF94 |
1.4893 |
1.5208 |
1.4782 |
1.3447 |
1.0722 |
1.0769 |
1.0785 |
108.32 |
|
Semi-emperical AM1 |
1.4601 |
1.5474 |
1.4977 |
1.3599 |
1.0762 |
1.0908 |
1.0859 |
107.18 |
|
Hartree-Fock 3-21G* |
1.4324 |
1.5120 |
1.5108 |
1.3203 |
1.0721 |
1.0754 |
1.0724 |
108.79 |
