The trans-trans isomer of dibenzalacetone is considered the most stable isomer due to its extended conjugation, lack of steric hindrance, and because it obeys the principles of the VSEPR (Valence Shell Electron Pair Repulsion) theory.
1. Extended conjugation: In the trans-trans configuration, the molecule has an extended conjugation between the double bonds and the carbonyl groups. This extended conjugation results in the delocalization of electrons along the molecule, which lowers the overall energy of the molecule, increasing its stability.
2. Lack of steric hindrance: Steric hindrance occurs when large substituent groups in a molecule repel each other, causing increased energy within the molecule. In the trans-trans isomer of dibenzalacetone, the bulky phenyl groups are oriented away from each other in the most stable position. This orientation reduces the repulsion between the two phenyl groups, which lowers the energy and increases the overall stability of the molecule.
3. Adherence to VSEPR theory: According to the VSEPR theory, the electron pairs surrounding an atom repel each other, and they will arrange themselves in a way that minimizes this repulsion. In the trans-trans isomer, the phenyl groups and carbonyl groups are distributed symmetrically, reducing electron pair repulsion, which subsequently minimizes the molecule's energy and enhances stability.
why is the trans-trans isomer of dibenzalacetone the most stable isomer?
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