What does h2 pdc do

Common catalysts used are insoluble metals such as palladium in the form Pd-C, platinum in the form PtO2, and nickel in the form Ra-Ni.

With the presence of a metal catalyst, the H-H bond in H2 cleaves, and each hydrogen attaches to the metal catalyst surface, forming metal-hydrogen bonds. The metal catalyst also absorbs the alkene onto its surface.

A hydrogen atom is then transferred to the alkene, forming a new C-H bond. A second hydrogen atom is transferred forming another C-H bond. At this point, two hydrogens have added to the carbons across the double bond.

Because of the physical arrangement of the alkene and the hydrogens on a flat metal catalyst surface, the two hydrogens must add to the same face of the double bond, displaying syn addition. Hydrogenation reactions are extensively used to create commercial goods. Hydrogenation is used in the food industry to make a large variety of manufactured goods, like spreads and shortenings, from liquid oils.

So that's one possible product. The other possibility, instead of having my two hydrogens as wedges, I can have my two hydrogens add as dashes. So there's a hydrogen and then here's a dash, and there's a hydrogen.

So at this top carbon here, now my ethyl group is coming out at me. And at this bottom carbon now my methyl group is coming out at me, like this.

So I have two possibilities. And if I look at these two products, I can see that they are enantiomers, they are mirror images of each other. So these two would be my enantiomers, and these would be the products of my reaction. So be very careful when thinking about syn additions here. Let's do one more example of a hydrogenation reaction. Let's do a bridged bicyclic compound. So let's look at a famous bridged bicyclic compound. Let's see if we can draw it here.

And then I'm going to draw that back carbon a little bit off like that. And my double bond is going to go right here. And then this is going to be a methyl group. And then up here there are going to be two methyl groups, like that. So this is alpha-pinene, found in turpentine.

And you can see there's an alkene on this. So if I took this alpha-pinene molecule and I wanted to hydrogenate it, I could use palladium and charcoal, palladium and carbon. And if I think about what happens in this mechanism, I know that my metal catalyst there, my palladium, is going to be flat, like that.

And so, when it has those hydrogens, when the palladium adsorbs those hydrogens, it's going to add those two hydrogens to my double bond, think about this guy over here, think about the alpha-pinene as molecules like a spaceship, right? And the spaceship is approaching the docking station. So the spaceship is slowly going down. The spaceship is going to approach the docking station.

And there's only one way the spaceship can approach the docking station. And that is the way in which we have drawn it right here. It could not flip upside down and approach it from the top, because of the steric hindrance of these methyl groups.

So this is the way that it approaches. In this part of the molecule, your alkene, is the flat part, right? So it's easiest for the molecule to approach in this way.

The spaceship analogy always helps my students. So there's only one product for this reaction. And let's see if we can draw it here. And let's see what it would look like. It would look something like this.

So we have our two methyl groups right here. So the hydrogens are going to add from below, right? So this hydrogen, let's say it adds right here. That's going to push this methyl group up.

So that methyl group gets pushed up when that hydrogen adds right down here. And then this other hydrogen is going to add to the opposite side. And so we can show the addition of that hydrogen. So there's my syn addition of these two hydrogens. Ask Question. Asked 6 years ago. Active 4 years, 1 month ago. Viewed 35k times. Improve this question.

Dissenter Dissenter In other words why isn't the product an allyl alcohol with no double bond? The reference given is House, Modern Synthetic Reactions , 2nd ed - so there might be info in there - and if nobody gets around to doing it, I will try to do some research when I am back in the UK.

Hudlicky, M. Show 1 more comment. Active Oldest Votes. Improve this answer. Jan At any rate, the bond must be broken at some point in the reaction. Add a comment.

Three metals—nickel, platinum and palladium—are commonly used, but a chemist cannot simply place a piece of one of these metals in a mixture of the alkene and hydrogen and get a reaction. Each metal catalyst must be prepared in a special way:. Other types of compounds containing multiple bonds, such as ketones, esters, and nitriles, do not react with hydrogen under the conditions used to hydrogenate alkenes. The examples below show reduction of an alkene, but the ketone and nitrile groups present remain intact and are not reduced.

Aromatic rings are also not reduced under the conditions used to reduce alkenes, although these rings appear to contain three carbon-carbon double bonds. As you will see later, aromatic rings do not really contain any double bonds, and many chemists prefer to represent the benzene ring as a hexagon with a circle inside it.

The representation of the benzene ring will be discussed further in Section The reaction between carbon-carbon double bonds and hydrogen provides a method of determining the number of double bonds present in a compound. For example, one mole of cyclohexene reacts with one mole of hydrogen to produce one mole of cyclohexane:.

A chemist would say that cyclohexene reacts with one equivalent of hydrogen, and 1,4-cyclohexadiene reacts with two equivalents of hydrogen. If you take a known amount of an unknown, unsaturated hydrocarbon and determine how much hydrogen it will absorb, you can readily determine the number of double bonds present in the hydrocarbon see question 2, below.

Addition of hydrogen to a carbon-carbon double bond is called hydrogenation. The overall effect of such an addition is the reductive removal of the double bond functional group.