Cyclopentadiene has a pKa = 15, where cyclopentane has a pKa > 50....
Explanation:
Cyclopentadiene has a pKa = 15, which is much lower than the pKa of cyclopentane (pKa = 50). This difference in acidity can be explained by the following reasons:
Cyclopentane contains no lone pairs:
Cyclopentane is a saturated hydrocarbon, which means that it contains no double or triple bonds. Therefore, it does not have any lone pairs that can contribute to its acidity. The acidity of cyclopentane is due to the presence of a weak C-H bond, which is much less acidic than a C=C bond.
Cyclopentadiene is a 4-Pi non-aromatic compound and after deprotonation it is aromatic:
Cyclopentadiene, on the other hand, is an unsaturated hydrocarbon that contains two double bonds. It is a 4-Pi non-aromatic compound, which means that it is not stable in its neutral form. However, after deprotonation, it becomes a 4-Pi aromatic compound, which is much more stable than its neutral form. The deprotonation of the cyclopentadiene molecule leads to the formation of a cyclopentadienyl anion, which is an aromatic compound.
In conclusion, the difference in acidity between cyclopentane and cyclopentadiene can be explained by the presence of double bonds in cyclopentadiene, which can contribute to its acidity through the formation of an aromatic compound after deprotonation.
Cyclopentadiene has a pKa = 15, where cyclopentane has a pKa > 50....
Since after deprotonation cyclopentadiene becomes stable by aromaticity, So, it will definitely have a higher acidic strength than that of cyclopentane and consequently lower pka value. Further ,no such stability factor has a role in case of cyclopentane so it has lower acidic strength comparatively.
Hope this helps.