7,12-Dimethylbenz[a]anthracene: refined structure, electron density distribution and endo-peroxide structure

Area of Science:

• Crystallography
• Chemical Physics
• Molecular Carcinogenesis

Background:

• 7,12-dimethylbenz[a]anthracene (DMBA) is a carcinogenic polycyclic aromatic hydrocarbon.
• Previous structural studies lacked detailed hydrogen atom positions and precise electron density analysis.

Purpose of the Study:

• To refine the crystal structure of DMBA at low temperature (180 K) for precise molecular geometry.
• To analyze the electron density distribution using multipole refinement.
• To investigate the structure of a DMBA endo-peroxide derivative.

Main Methods:

• X-ray diffraction at low temperature (180 K).
• Multipole refinement for electron density analysis.
• Computer graphics modeling of DMBA diol epoxides.

Main Results:

• Precise molecular geometry and hydrogen atom positions of DMBA determined.
• Significant steric strain and distortion observed in the bay region of DMBA.
• Electron density analysis reveals electron-rich bonds in the bay region and methyl groups, but not the K-region.
• 7- and 12-positions show electron deficiency, indicating high reactivity.
• Distortions and strain were also observed in the crystal structure of a DMBA endo-peroxide.

Conclusions:

• The refined structure of DMBA highlights significant molecular distortions due to steric overcrowding.
• Electron density distribution provides insights into the reactivity of DMBA, particularly at the 7- and 12-positions.
• Steric factors likely influence the conformation of DMBA diol epoxide isomers, relevant to their biological activity.