A LITTLE LIGHTBULB MOMENT
Alkenes, alkynes and addition reactions
Alkene hydrogenation makes a saturated alkane
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Nickel turns a carbon-carbon double bond into a single bond.
The idea behind the cue
Catalytic hydrogenation adds H2 across a C=C bond, usually with Pd, Pt, or Ni. The product is the corresponding alkane. This is reduction of unsaturation, not substitution or rearrangement.
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Short & simple
Nickel turns a carbon-carbon double bond into a single bond.
Acronym
HSA — Hungry Sloths Amble.
Story
A tiny alkene rides onto a metal surface and picks up two hydrogen atoms. The double bond disappears, and the molecule rolls away as a flatter, saturated alkane.
Connect the pieces
- H (Hungry) → Hydrogenation: Catalytic H2 adds across a C=C bond with Pd, Pt, or Ni, reducing unsaturation to the corresponding alkane.
- S (Sloths) → Saturated: The double bond is gone, so the product is fully saturated rather than still unsaturated.
- A (Amble) → Alkane: The final product is the matching alkane, not a substitution or rearrangement product.
- Hungry · Hydrogenation: Catalytic H2 adds across a C=C bond with Pd, Pt, or Ni, reducing unsaturation to the corresponding alkane.
- Sloths · Saturated: The double bond is gone, so the product is fully saturated rather than still unsaturated.
- Amble · Alkane: The final product is the matching alkane, not a substitution or rearrangement product.
Know the limits
Applies to alkene and alkyne reduction; it is not the usual outcome for aromatic rings under ordinary conditions.
Further reading · OpenStax Organic Chemistry ↗Check your understanding
What is the main product of catalytic hydrogenation of an alkene?
A. An alkane
B. A ketone
C. A vicinal dihalide
D. An alcohol
Reveal explanation
An alkane
Hydrogenation adds H2 across the double bond, fully saturating the alkene to an alkane.