Video Transcript
State the name of the following
molecule. (A) 4-Chloro-3-methylbut-1-yne, (B)
1-chloro-2-methylbut-3-yne, (C) 3-methyl-3-chloromethylprop-1-yne, (D)
1-chloro-2-ethynyl propane, or (E) 2-chloromethylbut-3-yne.
To answer this question, we need to
identify the name of this organic molecule. Organic molecules can be named
using the International Union of Pure and Applied Chemistry, or IUPAC, naming
rules.
First, we need to identify the
primary functional group in this molecule. We can see that the molecule
contains a carbon–carbon triple bond. This group is known as an alkyne
and is the primary functional group in this molecule.
Next, we need to identify and
number the longest continuous chain of carbon atoms in the molecule. The longest continuous chain must
contain the alkyne. And the alkyne must have the lowest
possible position number in the carbon chain. Following these rules, we can
identify two continuous chains of four carbon atoms that each contain the alkyne at
a position number of one. In the case of a tie like this, we
choose the chain that has the most branches or substituents. The green-numbered chain has one
large branch, but the pink-numbered chain has two branches. So we should choose the
pink-numbered chain to be the longest continuous chain of carbon atoms.
Next, we name the parent
alkyne. This name consists of a prefix that
indicates the number of carbon atoms in the carbon chain, a position number that
indicates the location of the alkyne in the carbon chain, and the suffix Y-N-E. The alkyne is located on carbon
number one. The prefix for four carbon atoms is
but-. So the name of the parent alkyne is
but-1-yne.
Next, we name each substituent. These names consist of a position
number, followed by the substituent name. Bonded to carbon number three,
there is a CH3 group, or a methyl group. So the name of the substituent is
3-methyl. Bonded to carbon number four is a
chlorine atom, giving us the name 4-chloro-. To complete the name of the
molecule, we write the substituent names in alphabetical order in front of the
parent name.
Therefore, the name of the molecule
shown is 4-chloro-3-methylbut-1-yne, answer choice (A).
