The major product formed in dehydrohalogenation reaction of 2-Bromo pentane is Pent-2-ene. This product formation is based on ?

The dehydrohalogenation of 2‑bromo‑pentane proceeds by an E2 elimination mechanism, where a base abstracts a β‑hydrogen and the C–Br bond breaks simultaneously, forming a double bond.

There are two possible β‑hydrogens that can be removed:

• Removal of the hydrogen on carbon‑1 gives Pent‑1‑ene (a terminal alkene).
• Removal of the hydrogen on carbon‑3 gives Pent‑2‑ene (an internal alkene).

According to Saytzeff’s (Zaitsev’s) Rule, the major product of an elimination reaction is the more substituted, and therefore more stable, alkene. Pent‑2‑ene has a double bond between carbon‑2 and carbon‑3, making it a disubstituted alkene, whereas Pent‑1‑ene is only monosubstituted.

Since a disubstituted alkene is thermodynamically more stable than a monosubstituted one, the reaction preferentially forms Pent‑2‑ene as the major product.

Thus, the formation of Pent‑2‑ene as the major product in the dehydrohalogenation of 2‑bromo‑pentane is explained by Saytzeff’s Rule.