Show the reactions involved for hydrogenation of all the...

Key Concepts

Hydrogenation Reaction

Hydrogenation is a chemical reaction that involves the addition of molecular hydrogen (H?) to unsaturated organic compounds. This reaction makes use of catalysts to facilitate the addition of hydrogen across double or triple bonds, converting alkenes into alkanes and alkynes into alkenes or further into alkanes. The process is widely applied in organic synthesis to convert unsaturated compounds into more saturated, stable products.

Alkenes

Alkenes are hydrocarbons that contain at least one carbon–carbon double bond, which is an area of high electron density making them particularly reactive. Their unsaturation enables them to undergo addition reactions, such as hydrogenation, where hydrogen atoms are added across the double bond to form alkanes.

Alkynes

Alkynes are hydrocarbons that contain a carbon–carbon triple bond, resulting in a linear geometry and a high degree of unsaturation. Due to the presence of two ?-bonds, alkynes can undergo hydrogenation reactions in a stepwise manner, first forming alkenes and then further transforming into alkanes when excess hydrogen and appropriate catalysts are applied.

Catalysis

Catalysis in hydrogenation involves the use of catalysts, typically heterogeneous metal catalysts like palladium, platinum, or nickel, to lower the activation energy of the reaction and increase the rate of hydrogen addition. These catalysts work by adsorbing both the hydrogen gas and the unsaturated substrate, enabling the efficient formation of new C–H bonds while minimizing side reactions.

Reaction Mechanism

The reaction mechanism of hydrogenation includes the adsorption of both the substrate and the hydrogen molecules onto the catalyst surface, followed by the dissociation of hydrogen into atomic hydrogen. These atoms then add to the unsaturated bonds of alkenes or alkynes in a concerted manner, resulting in a stepwise saturation process that ultimately yields a more stable alkane product. Each step in the mechanism is influenced by factors such as catalyst choice, temperature, and pressure.

Transcript

00:01 In this problem, we are trying to make two methylbutane, which looks like this, where we have a parent chain of four carbons with a methyl -substituent on the second carbon.

00:16 We want to synthesize this molecule using hydrogenation, which is a reaction in which we use a hydrogen molecule and a catalyst such as platinum to get rid of double bonds or triple bonds to give us an alkan molecule.

00:33 So the various different molecules that we can use to create this final product would be anything with a double bond or a triple bond that has the same number of carbons in this same arrangement.

00:48 So let's try to find a few different molecules.

00:53 So the first one that i can think of when i'm looking at this molecule is by putting the double bond right in the middle.

01:01 This is our first alken that we can make.

01:03 Let's pick another alken by moving this double bond.

01:06 We can also move the double bond to the first carbon between carbons 1 and 2.

01:10 That'll look like this.

01:19 Then we can move it to this carbon over here between carbons 4 and 3, which would change the numbering when you give it an iupac name, but it would look like this.

01:33 We can also put multiple double bonds, and that would still react via hydrogenation to create the same to methylbutane.

01:44 The only thing is that it might take a few more molecules of hydrogen.

01:49 So the only alken that we can make that has more than one double bond is by putting a double bond over here and putting a double bond over here.

02:00 We can't put a double bond in the middle because of this methyl group right here.

02:08 We can only have four attachments on each of the carbons.

02:13 So we can't put it in the middle and then put it on any of the adjacent molecules.

02:19 Otherwise, that would be going over the octet or carbon.

02:24 So now that we have all of the alkenes that we can make, we're going to try to make some triple bonds, so alkynes.

02:34 So the only place that we can put in alkyne is going to be between carbons 3 and 4 on the original molecule...

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