Question

Give the name of the product from the hydrogenation of each of the following: a. 1 -hexene b. 2 -methyl-2-butene c. propyne

Short answer

a. hexane, b. 2-methylbutane, c. propane

Step-by-step solution

Understand Hydrogenation

Hydrogenation is the chemical reaction between molecular hydrogen (H2) and another compound. In organic chemistry, it usually refers to the addition of hydrogen to a multiple bond.

Hydrogenation of 1-hexene

1-hexene is an alkene with the structure CH2=CH-(CH2)3-CH3. During hydrogenation, the double bond will be broken, and two hydrogen atoms will be added. The product will be hexane, CH3-(CH2)4-CH3.

Hydrogenation of 2-methyl-2-butene

2-methyl-2-butene is an alkene with the structure (CH3)2C=CH-CH3. During hydrogenation, the double bond will be broken, and two hydrogen atoms will be added. The product will be 2-methylbutane, (CH3)2CH-CH2-CH3.

Hydrogenation of Propyne

Propyne is an alkyne with the structure CH≡C-CH3. During hydrogenation, both of the triple bonds will be broken, and four hydrogen atoms will be added. The product will be propane, CH3-CH2-CH3.

Key concepts

alkene hydrogenation

Alkene hydrogenation is a pivotal reaction in organic chemistry. It involves the addition of hydrogen (H2) to an alkene, which contains a carbon-carbon double bond (C=C).
When hydrogen is added, the double bond is converted into a single bond (C-C), making the molecule more saturated and stable.
Catalysts like palladium, platinum, or nickel are often used to facilitate this reaction.

• Example: Hydrogenation of 1-hexene
1-hexene: CH2=CH-(CH2)3-CH3
• Product: Hexane (CH3-(CH2)4-CH3)

As you can see, the double bond in 1-hexene is turned into a single bond, and two additional hydrogen atoms are added to the carbon atoms initially involved in the double bond.

alkyne hydrogenation

Alkyne hydrogenation refers to the addition of hydrogen (H2) to an alkyne, which contains a carbon-carbon triple bond (C≡C).
This process converts the triple bond first into a double bond, and then into a single bond if excess hydrogen is used.
For complete hydrogenation, a similar catalyst used in alkene hydrogenation can be utilized.

• Example: Hydrogenation of Propyne
Propyne: CH≡C-CH3
• Product: Propane (CH3-CH2-CH3)

Initially, propyne converts into propene (CH2=CH-CH3) when one mole of H2 is added. With another mole of H2, propene converts to propane, completing the hydrogenation.

hydrocarbon structure

Hydrocarbons are the simplest organic compounds, consisting solely of carbon and hydrogen atoms. They can be classified based on the types of bonds between carbon atoms as alkanes, alkenes, and alkynes.

• Alkanes
Single bonds (C-C)
• Example: Methane (CH4)
• Alkenes
Double bonds (C=C)
• Example: Ethylene (CH2=CH2)
• Alkynes
Triple bonds (C≡C)
• Example: Acetylene (CH≡CH)
The structure of the hydrocarbon determines its reactivity and the types of reactions it can undergo, such as hydrogenation. Understanding these structures is fundamental to grasping more complex organic reactions.