Question

What is the best name for the molecule below? (2 points)

A compound with a total of nine carbons with a double bond and the rest single bonds. There is a straight chain of six carbons along the bottom with a double bond between the fifth and sixth carbons when counting from left to right. There is a propyl group branching off of the third carbon from the left.

4-ethyl-6-heptene
4-propyl-1-hexene
4-ethyl-1-heptene
3-propyl-5-hexene

Answer 1

Given:

A compound with:

Number of carbon atoms = 9
Number of double bonds = 1 
A double bond between 5th and 6th carbon
A propyl group (CH2CH2CH3) branching off the 3rd carbon from the left

Try to illustrate the given and observe the formation of the atoms. Now, follow the correct IUPAC naming system. The name of the compound is 

4-propyl-1-hexene

Count from the right to the left, the double bond is between the 1st and 2nd carbon, thus, 1-hexene. The propyl branches out the 4th carbon from the right, thus 4-propyl. 

Answer 2

Answer: 4-ethyl-1-heptene

Explanation: The IUPAC nomenclature follows following rules

1. The longest carbon chain is chosen which must include the functional groups, double and triple bonds.

2. The numbering of the chain starts from the end such that the functional group or the double or triple bond gets the lowest number.

3. The carbons which do not get any number are called as substituents.

The name starts with the number of the carbon bearing the substituent, followed by the name of the substituent. Thus 4-propyl. Then the word root is written which is the number of carbons in the longest chain. Thus it is hept. Then the suffix is the number and name of the functional group or double and triple bond. Thus 1-ene.

The name is 4-ethyl-1-heptene.