What is the IUPAC name for CH2=CH-CH2-CH3?

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Multiple Choice

What is the IUPAC name for CH2=CH-CH2-CH3?

Naming alkenes uses the longest carbon chain that contains the double bond and numbers to give the lowest possible locant for that double bond. In CH2=CH-CH2-CH3, the longest chain has four carbons and the double bond is between the first and second carbons when counted from the end that gives the lowest locant, so the double bond starts at carbon 1. The suffix -ene is used, and with four carbons the root is but-; there are no substituents or rings, so the correct IUPAC name is but-1-ene, commonly written as 1-butene. The other options don’t fit: five carbons would imply pent- or pentene, which isn’t present here; cyclobutane is a ring, not a chain; 2-methylpropene would require branching off the main chain, which this molecule does not have.

Naming alkenes uses the longest carbon chain that contains the double bond and numbers to give the lowest possible locant for that double bond. In CH2=CH-CH2-CH3, the longest chain has four carbons and the double bond is between the first and second carbons when counted from the end that gives the lowest locant, so the double bond starts at carbon 1. The suffix -ene is used, and with four carbons the root is but-; there are no substituents or rings, so the correct IUPAC name is but-1-ene, commonly written as 1-butene. The other options don’t fit: five carbons would imply pent- or pentene, which isn’t present here; cyclobutane is a ring, not a chain; 2-methylpropene would require branching off the main chain, which this molecule does not have.

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