Chapter 9, Problem 16P

Provide the IUPAC name for each of the following alkynes:

Interpretation Introduction

Interpretation:

IUPAC names for the given structures of alkyne are to be written.

Concept introduction:

The presence of a triple bond in a structure represents that the hydrocarbon is an alkyne.

To determine the name of the parent alkyne, select the longest continuous carbon chain containing the carbon‐carbon triple bond.

The parent name of the alkyne comes from the IUPAC name for the alkane having the same number of carbon atoms.

The numbers are assigned to the carbon atoms in the parent chain from the end which gives the lowest number to the substituents.

The name of any substituent atom or group and its location is indicated.

Name of substituent present in the structure is written before the name of the parent chain.

Answer to Problem 16P

Solution:

a) $\text{1-pentyne}$

b) $\text{2-pentyne}$

c) $\text{4,5-dimethyl-2-hexyne}$

d) $\text{5-cyclopropyl-1-pentyne}$

e) $\text{cyclotridecyne}$

f) $\text{4-butyl-2-decyne}$

g) $\text{2,2,5,5-tetramethyl-3-hexyne}$

Explanation of Solution

a) The structure is:

The given structure contains a triple bond. There are $5$ carbon atoms in the longest chain. Hence the parent alkyne is pentyne. The position of the triple bond is between carbon number $\text{1 and 2}$. Hence the name for the given structure is $\text{1-pentyne}$.

b) The structure is:

The given structure contains a triple bond. There are $5$ carbon atoms in the longest chain. Hence the parent alkyne is pentyne. The position of the triple bond is between carbon number $\text{2 and 3}$.

Hence the name for the given structure is $\text{2-pentyne}$.

c) The structure is:

The longest chain in the given structure containing the triple bonded carbon atoms consists of $6$ atoms; hence the parent alkyne is hexyne. The chain is numbered such that the triple bonded carbon atoms get the lowest numbers. The triple bond is present between carbon number $\text{2 and 3}$. Two methyl groups are attached to the carbon number $\text{4 and 5}$. So the IUPAC name for the given structure is $\text{4,5-dimethyl-2-hexyne}$.

d) The structure is:

The longest chain in the given structure containing the triple bonded carbon atoms consists of $5$ atoms; therefore, the parent alkyne is pentyne. The longest carbon chain containing the triple bond is numbered such that the triple bonded carbon atoms get the lowest numbers. The triple bond is present between carbon number $\text{1 and 2}$. A cyclopropyl group is attached to the carbon number $\text{ 5}$. So the IUPAC name for the given structure is $\text{5-cyclopropyl-1-pentyne}$.

e) The structure is:

The longest chain in the given structure containing the triple bonded carbon atoms consists of $13$ atoms and is cyclic. Hence the parent alkyne is tridecyne. The ring is numbered such that the triple bonded carbon atoms get the lowest numbers. The triple bond is present between carbon number $\text{1 and 2}$. Hence the IUPAC name for the structure is $\text{cyclotridecyne}$.

f) The structure is:

The longest chain in the given structure containing the triple bonded carbon atoms consists of $10$ atoms; therefore, the parent alkyne is decyne. The chain is numbered such that the triple bonded carbon atoms get the lowest numbers. The triple bond is present between carbon number $\text{2 and 3}$. A butyl group is attached to the carbon number $4$. Hence the IUPAC name for the given structure is $\text{4-butyl-2-decyne}$.

g) The structure is:

The longest chain in the given structure containing the triple bonded carbon atoms consists of $6$ atoms; hence the parent alkyne is hexyne. The chain is numbered such that the triple bonded carbon atoms get the lowest numbers. The triple bond is present between carbon number $\text{3 and 4}$. Two methyl groups are attached to the carbon number $2$, and two methyl groups are attached to the carbon number $5$. In all, there are four methyl groups attached to the parent chain. Hence the IUPAC name for the given structure is $\text{2,2,5,5-tetramethyl-3-hexyne}$.