Write Lewis structures for the cis–trans isomers of CH3CH = CHCl

Write Lewis structures for the cis–trans isomers of CH3CH = CHCl.

The correct answer and explanation is :

To draw the Lewis structures for the cis–trans isomers of CH₃CH=CHCl, we need to first understand the molecule’s structure. The molecule has three carbon atoms, two hydrogens (H), one chlorine (Cl), and a double bond between the second and third carbon atoms. The two isomers differ in the relative positions of the substituents (the chlorine and the methyl group) on the double bond.

Step-by-step approach to drawing the Lewis structures:

1. Identify the structure: The compound consists of a propene skeleton with a methyl group (CH₃) on the first carbon and a chlorine (Cl) on the third carbon. The central carbon-carbon double bond is between the second and third carbon atoms. The general formula is:

• CH₃-CH=CHCl

1. Bonding: The double bond between carbon atoms 2 and 3 forms a rigid plane, so the relative positions of the methyl group (CH₃) and chlorine (Cl) can either be on the same side or opposite sides of this double bond.

Lewis Structure of the cis-isomer (Z-isomer):

• In the cis-isomer, the methyl group (CH₃) and chlorine (Cl) are positioned on the same side of the double bond. The bond angles around each carbon are approximately 120°. Lewis Structure:

      H   CH₃
       |    |
    H—C = C—Cl
       |    |
       H   H

Lewis Structure of the trans-isomer (E-isomer):

• In the trans-isomer, the methyl group (CH₃) and chlorine (Cl) are positioned on opposite sides of the double bond. Lewis Structure:

      CH₃    H
       |     |
    H—C = C—Cl
       |     |
       H     H

Explanation:

The cis and trans isomerism occurs due to the restricted rotation around the carbon-carbon double bond. Since the double bond holds the carbon atoms in place, the substituents (CH₃ and Cl) can either be on the same side (cis) or on the opposite sides (trans) of the bond.

• In the cis-isomer, the same side positioning results in dipole interaction due to the polarity of the chlorine atom, which affects the physical properties like boiling point.
• In the trans-isomer, the opposite side arrangement leads to less polarity and typically a lower boiling point than the cis counterpart.

The cis-trans isomerism significantly affects the molecule’s physical and chemical properties, as the steric and electronic environments differ between the two isomers.