Video Transcript
What is the major product produced
in the addition reaction of hydrogen bromide and propene? (A) Compound one, (B) compound
two.
An addition reaction is a type of
chemical reaction where two or more molecules combine to form a single type of
molecular product. We are shown that the addition
reaction of hydrogen bromide and propene could produce two different products. We need to determine which of the
compounds is the major product of this reaction, or in other words which of the
compounds is most likely to be produced.
Propene is an alkene, a compound
which contains an electron-rich carbon-carbon double bond. Alkenes react with hydrogen
halides, like hydrogen bromide, in a hydrohalogenation reaction, a type of addition
reaction. Over the course of this reaction,
the 𝜋 bond between the two carbon atoms will break as will the bond between the
hydrogen and halogen atoms. This loss of bonds will allow for
the formation of a new carbon-hydrogen bond and a new carbon-halogen bond. The product of this reaction is a
haloalkane.
In this example, we chose to add
the hydrogen atom to the carbon on the left and the halogen atom to the carbon on
the right. But if this were reversed, the
product would still be the same. This is because the starting alkene
is symmetrical. Propene is an unsymmetrical
alkene. This affects how the hydrogen and
halogen atoms will add to the molecule.
In general, we can predict the
major product of the hydrohalogenation of an unsymmetrical alkene using
Markovnikov’s rule. Markovnikov’s rule states that the
acidic hydrogen atom will add to the carbon of the double bond that has the greatest
number of hydrogen substituents. Looking at propene, the carbon of
the double bond that has the greatest number of hydrogen substituents is the carbon
atom on the right. So during the reaction, the
hydrogen of hydrogen bromide should form a bond with this carbon atom. This means that bromine must form a
bond with the other carbon atom of the double bond, the carbon atom in the center of
the structure.
Looking at the compounds, we can
see that the compound which shows a new hydrogen atom bonded to the carbon on the
right and a bromine atom bonded to the carbon in the middle of the structure is
compound one. Therefore, the major product
produced in the addition reaction of hydrogen bromide and propene is compound one,
answer choice (A).
