MHT-CET Chemistry · Alkynes
Alkynes: Haloalkynes and Hybridisation
An alkyne has a C≡C triple bond whose two carbons are sp hybridised; a haloalkyne has its halogen on one of those triple-bond carbons.
Why this matters
3 PYQs. Two ask which structure is a haloalkyne, set twice in 2024; one counts sp² carbons in a diyne. One card.
Concept 1 of 1: Haloalkynes and the Hybridisation of Carbon
The name follows where the halogen sits. On a triple-bond carbon it is a haloalkyne; one carbon away it is propargylic; on a double-bond carbon it is a haloalkene. The hybridisation follows the bond: triple bond sp, double bond sp², single bonds only sp³.
Definition
- Haloalkyne: X bonded to an sp carbon of C≡C — CH₃CH₂C≡C–X, chloroethyne HC≡C–Cl.
- X on the carbon next to C≡C (CH₃C≡C–CH₂X, 3-chlorobut-1-yne) is propargylic, not a haloalkyne.
- Hybridisation: C≡C carbons sp; C=C carbons sp²; saturated carbons sp³.
- Hexa-1,4-diyne HC≡C–CH₂–C≡C–CH₃ has no sp² carbon.
Practice this conceptself-check
The same idea in a real exam question:
MHT-CET · 2024 · 12th May Shift 2 · Q58Moderate
Example 1 · Alkynes · Nomenclature and Identification of Alkynes
Which among the following is haloalkyne?
Any halogen in an alkyne
A halogen anywhere in the molecule does not make a haloalkyne. It must sit on the C≡C carbon itself.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (1)
Watch out for (1)
- Any halogen in an alkyne→ Haloalkynes and the Hybridisation of Carbon
Test yourself on a real paper
Sit a past MHT-CET paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.