Question

The ketone tropone, is exceptionally basic in character, forming much more stable salts with \(\mathrm{HCl}\) than simple ketones. How can this be explained?

Short answer

Tropone has a higher basicity compared to simple ketones due to the strong delocalization of electrons and resonance stabilization within its structure. This increased electron delocalization enhances the availability of electron pairs for reaction with HCl. Consequently, when tropone reacts with HCl, it forms more stable salts through protonation of the oxygen atom, as the delocalized electrons and resonance stabilization contribute to the energy-lowering effect within the tropone structure.

Step-by-step solution

Understanding the Structure of Tropone

First, we need to understand the structure of tropone. Tropone is a seven-membered ring having six carbons and one oxygen atom. Each carbon atom has a double bond with either of its neighboring carbons, except for one carbon which has a double bond with the oxygen atom. The structure can be represented as follows: \[ \chemfig{*6(=-=-(-(-[::+60]\chemabove{O}{\oplus}-[::-60]-)(-[:-150]))-=)} \] The positive charge on the oxygen atom indicates that this is a resonance structure, and we can draw several resonance structures to represent the tropone molecule more accurately. Tropone exhibits resonance stabilization due to the delocalization of electrons.

Comparing Basicity of Tropone and Simple Ketones

Tropone's higher basicity compared to simple ketones can be attributed to the delocalization of electrons and resonance stabilization. In simple ketones, the oxygen atom is involved in a double bond with a carbon atom, which in turn makes electron pairs on the oxygen atom less readily available to react with HCl. This decreases the basic character of simple ketones. However, in tropone, the electrons are delocalized throughout the ring, which increases the availability of electron pairs for reaction with HCl. This enhanced electron delocalization contributes to the higher basic character of tropone.

Explaining the Formation of More Stable Salts

When tropone reacts with HCl, it forms a salt through protonation of the oxygen atom. Due to the electron delocalization and resonance stabilization, the resulting salt is more stable compared to the salts formed by simple ketones. In other words, the increased stability of the tropone-HCl salts can be linked to the energy-lowering effect of the delocalized electrons and resonance stabilization within the tropone structure. In summary, the higher basicity and increased stability of salts formed by tropone with HCl can be explained by the strong delocalization of electrons and resonance stabilization within tropone's structure.