Q8P - Organic Chemistry (Mcmurry)

Question

The sex attractant of the common housefly is an alkene $cis-\mathbf{9}-\mathbf{tricosene}$ named. Draw its structure. (Tricosane is the straight-chain alkane ${\mathbf{C}}_{23}{\mathbf{H}}_{48}$ .)   

Step-by-Step Solution

Answer

Structure of the compound is:

Step 1: Naming of alkene

There are rules for naming alkene:

• Name the parent hydrocarbon: Look for the longest carbon chain having the double bond, then name the compound accordingly. Suffix –ene is used for alkenes

 

• Number the carbon atoms in the chain: Start numbering from the carbon nearer to the double bond but when double bond is equidistant from both sides then start numbering from carbon nearer to the first branch point. So, double-bond carbons receive the lowest possible numbering.

 

• Write the full name: Number the substituents according to their positions in chain, and write them in alphabetical order. Position of the double bond is indicated by the number of first alkene carbon and placing that number directly before the parent name.

 

•  If more than one double bond is present then use one of the suffixes as -diene, -triene, and so on based on number of double bonds and indicate the position of each immediately before suffix –ene.

 

• Cycloalkene are named same way, but because here is no end so number the cycloalkene so double bond is taken between C1and C2. It is not necessary to indicate the position of the double bond in the name because it’s always between C1 and C2.

Step 2: Cis and Trans configuration

Cis configuration is when two groups are on the same face of the double and trans configuration is when the groups are on opposite faces. 

Both isomers are stable and neither can be converted into the other without breaking and reforming chemical bonds. 

Cis alkenes are less stable than their trans forms as there is steric strain between the two bulky substituents on the same side of the double bond. 

Step 3: Structure of given compound

Structure of a given compound is known from the fact that:

• The Ninth position is cis so the double bond is between C9 and C10.
• Tricosane has twenty-three carbon and forty-eight hydrogen.

Structure of given compound