Question

Draw the condensed structural formulas for the cis and trans isomers of 2 -pentene. Can cyclopentene exhibit cis-trans isomerism? Explain.

Short answer

The condensed structural formulas for cis-2-pentene and trans-2-pentene are: Cis-2-pentene: \(CH_3-CH=CH-CH_2-CH_3\) Trans-2-pentene: \(CH_3-CH=CH-CH_2-CH_3\) Cyclopentene cannot exhibit cis-trans isomerism because it has a cyclic structure with no substituent groups attached to the double-bonded carbons.

Step-by-step solution

Understanding cis and trans isomerism

Cis and trans isomerism (also called geometric isomerism) occurs in alkenes with a carbon-carbon double bond. It refers to the arrangement of atoms or groups around the double bond. In cis isomers, the two largest substituent groups are on the same side of the double bond, while in trans isomers they are on opposite sides.

Drawing the condensed structural formulas for 2-pentene

2-pentene has the molecular formula C5H10, with a double bond between C2 and C3. For the cis isomer (cis-2-pentene), the two methyl (CH3) groups are on the same side of the double bond: \(CH_3-CH=CH-CH_2-CH_3\) For the trans isomer (trans-2-pentene), the two methyl (CH3) groups are on opposite sides of the double bond: \(CH_3-CH=CH-CH_2-CH_3\)

Determining the possibility of cis-trans isomerism in cyclopentene

Cyclopentene is a cyclic alkene with five carbon atoms and one double bond in the ring. The double bond prevents the molecule from rotating, which could potentially allow for cis-trans isomerism. However, since the molecule is cyclic and all carbon atoms are part of the ring structure, there are no substituent groups (such as methyl or other alkyl groups) directly attached to the double-bonded carbons that would allow for the occurrence of geometric isomerism. Therefore, cyclopentene cannot exhibit cis-trans isomerism. In summary, we have drawn the condensed structural formulas for cis-2-pentene and trans-2-pentene, and determined that cyclopentene cannot exhibit cis-trans isomerism due to its cyclic structure and lack of substituent groups attached to the double-bonded carbons.