Draw all alkenes that react with one equivalent of H2 in the presence of a palladium catalyst to

Draw all alkenes that react with one equivalent of H2 in the...

Key Concepts

Constitutional Isomers

Constitutional isomers are compounds that share the same molecular formula but differ in the connectivity of their atoms. When considering all alkenes that could potentially yield a specific alkane upon hydrogenation, it is important to account for these different connectivities as they represent distinct chemical entities and reactivity profiles, even though the final products may be the same alkane.

Palladium Catalyst

A palladium catalyst is commonly used in hydrogenation reactions due to its ability to adsorb both the alkene and hydrogen onto its surface. This facilitates the addition of hydrogen atoms onto the double bond in a controlled, often syn-addition manner. The catalyst lowers the activation energy, making the reaction proceed at a faster rate under milder conditions.

Hydrogenation Reaction

Hydrogenation is the process of adding hydrogen (H?) across a double bond of an alkene to convert it into an alkane. The reaction typically occurs under catalytic conditions, effectively saturating the molecule with hydrogen atoms. In this context, using one equivalent of hydrogen means that each alkene molecule reacts with one mole of H?, leading to a fully saturated alkane.

Alkenes

Alkenes are unsaturated hydrocarbons characterized by at least one carbon-carbon double bond. Their reactivity arises from this double bond, which allows them to participate in addition reactions, such as hydrogenation. The structure and position of the double bond can vary, giving rise to different molecules even with the same molecular formula.

Transcript

00:02 This is the answer to chapter 12, problem number three from the smith organic chemistry textbook.

00:10 And in this problem, we're asked to look at these three molecules, these three alkanes, and to consider the alkenes, which could be hydrogenated, in order to produce these alkanes.

00:24 And so basically, we're working backwards.

00:27 That's what these arrows with the two lines and the big arrowhead mean.

00:32 Is that we're showing where these molecules could have come from.

00:37 And so basically, the core structure of the molecule is not going to change.

00:43 And we're just going to think about where could we have a double bond or have had a double bond.

00:49 So for a, that would work.

00:56 This would also work.

01:02 And this would also work.

01:04 And so you might be tempted to say, well, what about a fourth one where we put a double bond on this other methyl group here, so like that.

01:16 But of course, you should remember that that would be really just drawing the exact same thing that we already drew as the third isomer here.

01:26 So it's important not to draw structures that are actually the same structure and mistake them for.

01:34 Different structures.

01:36 So for example, looking at b, at first you might think, well, there are a lot of choices here in b for places that we could put a double bond, but actually there's only two.

01:50 So we could put a double bond here.

01:56 And we could also put a double bond here.

02:04 And that's it...

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