I have a question that say 2-butyne reacts with hydrogen and butane is the product. Wouldn't 2-butene be the product because there are only 2 hydrogens and therefore they can only break one bond not 2.
Yes and no. If 1 mole H2 is added to a mole of 2-butyne, then 2-butene is formed but if TWO moles H2 are added to a mole of 2-butyne, then the product is butane.
CH3C(triplebond)CCH3 + H2 ==> CH3CH=CHCH3.
The problem is stopping it half-way home.
CH3C(triplebond)CCH3 + 2H2 ==> CH3CH2CH2CH3
Usually a catalyst is added to help things along and once it gets started its tough to stop it at the -ene stage.
OK, thanks DrBob :)
The reaction you are referring to is a hydrogenation reaction, where 2-butyne reacts with hydrogen to produce a saturated hydrocarbon. In this case, the product should indeed be 2-butene rather than butane.
When 2-butyne reacts with hydrogen, the hydrogen molecules add across the triple bond to form a saturated molecule. Since 2-butyne has two triple bonds, the hydrogenation reaction occurs twice, breaking both of the triple bonds and adding a total of four hydrogen atoms.
The double bond only forms at the positions where the original triple bond was present. Therefore, the resulting product is 2-butene, not butane.
The reaction you mentioned involves the addition of hydrogen to 2-butyne, resulting in the formation of a new compound. Let's break it down step by step to understand the product formed.
2-butyne is a molecule with a triple bond between the second and third carbon atoms:
CH₃-CH≡C-CH₃
The reaction involves the addition of hydrogen (H₂) to the triple bond. Hydrogen gas (H₂) is a source of two hydrogen atoms (H⁻) that can add to the carbon atoms in the triple bond.
When we add hydrogen to a triple bond, the reaction proceeds in a stepwise manner, adding one hydrogen atom at a time. The first hydrogen atom adds to one of the carbon atoms, resulting in the formation of a double bond. The molecule then has a new functional group called an alkene.
So, one hydrogen atom adds to 2-butyne, resulting in the formation of a double bond. The molecule formed is 2-buten-1-yne:
CH₃-CH=CH-CH₃
After the addition of the first hydrogen, we still have another hydrogen available to react with the double bond. This second hydrogen atom adds to the remaining carbon atom in the double bond, leading to the elimination of the triple bond entirely. As a result, a saturated hydrocarbon with a single bond is formed.
The final product is butane:
CH₃-CH₂-CH₂-CH₃
So, in the given reaction, the product formed after the addition of hydrogen to 2-butyne is indeed butane, not 2-butene. The two available hydrogen atoms can break two bonds: one from the triple bond and another from the double bond, resulting in the conversion of 2-butyne to butane.