Experiment 2- Catalytic Alkene Hydrogenation

Question 1

Define Hydrogenation

Answer 1

Addition of the H2 molecule across a unit of unsaturation (examples of unsaturation are alkenes and carbonyls).

Question 2

What is another way to view unsaturation?

Answer 2

To see all the carbons that as sp^3 hybridized.

Question 3

What are triacylglycerides?

Answer 3

They are fats, made from condensing glycerol with 3 molecules of fatty acids.

Question 4

Triacylglycerides with _____ are unsaturated and are considered good fats.

Answer 4

Cis-Alkenes

Question 5

What is the allylic position in alkenes?

Answer 5

The position adjacent to the carbon involved in the double bond.

Question 6

Why are unsaturated fats considered worst than saturated fats?

Answer 6

This is becasue they have a shorter shelf life. The reason for this is the allylic hydrogens in the alkene are susceptible to oxidation, rendering the oil rancid upon the reaction.

Question 7

What are all oils consisted of?

Answer 7

Saturated and unsaturated fats.

Question 8

Can unsaturated fats contain trans alkenes?

Answer 8

Yes, they can.

Question 9

What is INCORRECT about unsaturated fats?

Answer 9

They are STABLE.

Question 10

What are the bad things that can happen when you have alkenes present (unsaturation) in oils?

Answer 10

Light can convert the cis-alkene into a trans-alkene, effectively making it a trans fat. Also, the hydrogen on the allylic position can be oxidized, rendering the oil rancid.

Question 11

What happens with hydrogenation reactions?

Answer 11

The double bond is broken and hydrogens are added across the double bond.

Question 12

What can happen with he hydrogenation of oils?

Answer 12

Some of the cis-alkenes can partially isomerize into trans-alkenes. Since trans-alkenes are more stable, they are harder to hydrogenate.

Question 13

What is being done in this experiment?

Answer 13

Hydrogenation of Ethyl Cinnamate through palladium catalysis.

Question 14

What does the suffix “ate” refer to?

Answer 14

Refers to the CO2 motif in esters.

Question 15

What are the reaction conditions for this experiment? Why does this deviate from the norm?

Answer 15

The source of hydrogens will be ammonium formate as opposed to molecular hydrogen. Molecular hydrogen + oxygen lead to a highly exothermic reaction.

Question 16

Define Transfer Hydrogenation

Answer 16

A reaction in where hydrogen is transferred from one entity to the other is called a transfer hydrogenation.

Question 17

What happens in the ammonium formate-mediated transfer hydrogenation scheme?

Answer 17

The lone pair on the oxygen from the formate turns into a pi bond, making CO2. From there, the C-H bond is broken, so that a hydride is transferred to the palladium. Then, the negatively charged hydrogen does a proton transfer onto ammonium, leading to the presence of 2 hydrogen on the surface of palladium.

Question 18

Does ammonium formate contain an H-H bond?

Answer 18

No, it does not. The ammonium cation contains the H+ and the formate anion contains the H- .

Question 19

Define Reduction Reactions.

Answer 19

Hydrogenation reactions where carbons form new bonds to hydrogen are called reduction reactions.

Question 20

What is the role of Pd/C in this experiment

Answer 20

It is sued for the hydrogenation process.

Question 21

What does the term “reflux” refer to?

Answer 21

It means the boiling and immediate condensation of the solvent.

Question 22

Where does water flow take place in the condenser? How must the tubes be oriented?

Answer 22

From bottom to up. The bottom tube allows for the flow of water, whereas the top tube allows for the water to be moved out.

Question 23

Between Diethyl Ether (Et2O) and water, which make the organic adds aqueous layer respectively?

Answer 23

Et2O makes the organic layer and H2O makes the aqueous layer.

Question 24

Define Chromophore

Answer 24

The part of the molecule that is responsible for absorbing the light is called the chromophore.

Question 25

What is required in a molecule for it to be able to absorb UV light?

Answer 25

A chromophore.

Question 26

What sort of bonding to chromophore usually involve?

Answer 26

Conjugated double bonds.

Question 27

What happens when we put a TLC plate under UV radiation? What does it mean when we see nothing under the UV light?

Answer 27

The chromophores absorb the UV light, reflecting another color. When we see nothing under the UV light, it doesn’t mean that nothing is there. The reason we don’t see anything is because the molecule doesn’t contain a chromophore. In this case, we simply add KMnO4 solution, a TLC stain, which works by oxidizing oxidizable functional groups present in the molecule, allowing us to see color.