Exhaustive hydrogenation of 1-hexyne with hydrogen and a poisoned catalyst gives which product?

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Multiple Choice

Exhaustive hydrogenation of 1-hexyne with hydrogen and a poisoned catalyst gives which product?

Using a poisoned catalyst in hydrogenation changes what happens after the first addition of hydrogen. A poisoned catalyst, like Lindlar’s catalyst, slows or stops further hydrogenation, so an alkyne is reduced only once to an alkene and doesn’t go on to become an alkane. The hydrogen atoms add from the same face of the alkyne on the catalyst surface (syn addition), so the two hydrogen atoms end up on the same side of the newly formed double bond. That gives cis-1-hexene as the product from 1-hexyne. If the catalyst weren’t poisoned, the double bond would be hydrogenated again to give hexane. The other options—forming trans-hexene or an alcohol—don’t arise under these conditions.

Using a poisoned catalyst in hydrogenation changes what happens after the first addition of hydrogen. A poisoned catalyst, like Lindlar’s catalyst, slows or stops further hydrogenation, so an alkyne is reduced only once to an alkene and doesn’t go on to become an alkane. The hydrogen atoms add from the same face of the alkyne on the catalyst surface (syn addition), so the two hydrogen atoms end up on the same side of the newly formed double bond. That gives cis-1-hexene as the product from 1-hexyne.

If the catalyst weren’t poisoned, the double bond would be hydrogenated again to give hexane. The other options—forming trans-hexene or an alcohol—don’t arise under these conditions.

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