Video Transcript
What is the name of the product
formed during this addition reaction between ethene and chlorine gas? (A) 1,1-Dichloroethane, (B)
chloroethane, (C) chloroethene, (D) 1,1-dichloroethene, or (E)
1,2-dichloroethane.
An addition reaction is a type of
chemical reaction where two or more molecules combine to form a larger molecule
without any by-products forming. In this addition reaction, ethene
is being combined with chlorine gas. As chlorine is a halogen, we can
further classify this type of addition reaction as a halogenation reaction, an
addition reaction involving the addition of one or more halogens.
The chlorine atoms in this reaction
will be added to ethene. Ethene is an alkene, a compound
which contains an electron-rich carbon–carbon double bond.
Let’s consider what happens during
the halogenation of a generic alkene with a generic diatomic halogen. Over the course of this reaction,
the 𝜋 bond between the two carbon atoms will break, as will the bond between the
two halogen atoms. This loss of bonds allows for the
formation of two new carbon–halogen single bonds. The product of this reaction no
longer contains a carbon–carbon double bond, but it does contain two halogen atoms
that are attached to adjacent carbon atoms.
With this in mind, let’s take
another look at the reaction provided in the question. We know that the 𝜋 bond between
the two carbon atoms will break along with the bond between the two chlorine
atoms. This will allow for the formation
of two new carbon–chlorine single bonds. The product of this reaction no
longer contains a carbon–carbon double bond, but it does contain two carbon–chlorine
single bonds.
Now that we know the product, we
need to determine its name. The longest continuous chain of
carbon atoms in this compound is two-carbon-atoms long, so the name will contain the
term eth- to indicate that the longest continuous chain is two-carbon-atoms
long. The carbon atoms are joined
together by a single bond. So we’ll use the suffix -ane to
indicate the type of bond between the carbon atoms. There are two chlorine substituents
bonded to ethane, so we can add dichloro- to the name. Chloro- is the name of a chlorine
substituent, and di- indicates that there are two of these substituents.
Finally, we need to indicate where
the chlorine atoms are located in the molecule. One chlorine atom is bonded to
carbon number one, and one chlorine atom is bonded to carbon number two. Adding these position numbers to
the beginning of the name, we get the name 1,2-dichloroethane. This matches answer choice (E).
Therefore, the name of the product
formed during the addition reaction between ethene and chlorine gas is
1,2-dichloroethane, answer choice (E).
