Name this molecule: CH2 CH CH2 CH2 CH3.

Name this molecule: CH2 CH CH2 CH2 CH3.

• A. Pent-1-ene
• B. Pent-2-ene
• C. Pentane
• D. Hex-1-ene

Answer: (A)

This question tests naming alkenes using the longest carbon chain that contains the C=C and the position of that double bond. Look at the structure CH2=CH-CH2-CH2-CH3: there are five carbon atoms in the main chain, so the base name is pent- (five carbons). The molecule has a C=C bond, so we use the -ene ending. The double bond starts at the first carbon when counted from either end, giving the locant 1. Put together, the name is pent-1-ene. If you tried pent-2-ene, that would mean the double bond is between carbons 2 and 3, which isn’t the case here. Hex-1-ene would mean six carbons, which isn’t correct for this structure.

This question tests naming alkenes using the longest carbon chain that contains the C=C and the position of that double bond. Look at the structure CH2=CH-CH2-CH2-CH3: there are five carbon atoms in the main chain, so the base name is pent- (five carbons). The molecule has a C=C bond, so we use the -ene ending. The double bond starts at the first carbon when counted from either end, giving the locant 1. Put together, the name is pent-1-ene. If you tried pent-2-ene, that would mean the double bond is between carbons 2 and 3, which isn’t the case here. Hex-1-ene would mean six carbons, which isn’t correct for this structure.