sketch of C3H5+ that shows all of the partial charges for each atom
The correct answer and explanation is :
The molecular ion C₃H₅⁺, commonly known as the allyl cation, is a positively charged species. It is a resonance-stabilized molecule, where the positive charge is delocalized over the carbon atoms in the structure. Let’s break down the structure and partial charges.
Structure of C₃H₅⁺ (Allyl Cation):
The structure of the allyl cation consists of three carbon atoms (C) and five hydrogen atoms (H). The central carbon (C₂) is sp² hybridized, while the other two carbons (C₁ and C₃) are also sp² hybridized. The cation is stabilized by resonance, where the positive charge is delocalized across the three carbon atoms.
A typical representation of the resonance forms looks like this:
- The central carbon (C₂) holds the positive charge in one resonance form.
- In another resonance form, the positive charge can be located on the carbon C₁ or C₃, spreading the charge over the three carbon atoms.
Resonance Forms:
- First resonance form: The positive charge is located on the central carbon (C₂).
- Second resonance form: The positive charge is delocalized on C₁.
- Third resonance form: The positive charge is delocalized on C₃.
Partial Charges:
- C₁ and C₃: These carbons are slightly partial positive charges due to their involvement in the resonance. The positive charge is not fully localized on them but is distributed through resonance.
- C₂ (Central carbon): The central carbon experiences the highest partial positive charge due to the fact that it is involved in resonance and is directly bonded to two hydrogen atoms.
- Hydrogens (H): The hydrogens in the molecule are neutral, but they could slightly carry a partial positive charge as they are bonded to the carbon atoms that bear a partial positive charge.
Delocalization of the Positive Charge:
The charge delocalization makes the allyl cation relatively stable compared to an isolated primary cation, and the partial positive charges on the carbon atoms result from the delocalization of the cationic center over all three carbons.
The resonance stabilization and delocalization lead to a more symmetric distribution of electron density, thus lowering the overall energy of the system.