Chapter 19: Problem 22

What rule must be followed when the carbon atoms in an alkene or alkyne is numbered?

Short Answer

Expert verified

The rule that needs to be followed when numbering carbon atoms in an alkene or alkyne is that numbering should begin from the end of the chain closest to the double or triple bond. This is to assign the lowest possible number to the carbon atom involved in the double or triple bond.

Step by step solution

Understanding Alkenes and Alkynes

Alkenes and alkynes are unsaturated hydrocarbons. Alkenes contain a carbon-carbon double bond while alkynes contain a carbon-carbon triple bond. The positioning of these bonds in the molecule defines the structural isomers of alkenes and alkynes.

Rules for Numbering

According to the IUPAC nomenclature rules, when numbering the carbon atoms in alkenes and alkynes, the numbering should begin from the end of the chain closest to the double or triple bond, respectively. This rule is in place to assign the lowest possible number to the carbon atom involved in the multiple bond.

Identifying Isomers

Due to this rule, structurally different compounds, or isomers, will have different names. This rule helps identify the position of the double or triple bond in the chain of carbon atoms. For instance, in pentene (an alkene), pent-1-ene would have the double bond starting from carbon 1, while pent-2-ene would have the double bond starting from carbon 2, indicating different structures.

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What rule must be followed when the carbon atoms in an alkene or alkyne is numbered?

Short Answer

Step by step solution

Understanding Alkenes and Alkynes

Rules for Numbering

Identifying Isomers

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