Page 8 Flashcards
Why is there free rotation about single bonds but restricted rotation about double bonds?
A: Single bonds allow free rotation due to the sigma (σ) bond, but double bonds restrict rotation because the pi (π) bond requires specific orbital alignment.
What happens when a single bond rotates 180 degrees?
A: The molecule interconverts between conformations, such as anti and eclipsed, but remains the same molecule.
A: The overlapping p orbitals in the pi bond must remain aligned, which prevents rotation.
Why can’t double bonds rotate freely?
What is the difference between cis and trans isomers in alkenes?
A: Cis isomers have substituents on the same side of the double bond, while trans isomers have substituents on opposite sides.
Can cis and trans isomers interconvert by rotation around the double bond?
A: No, they cannot interconvert by rotation because breaking the π bond is required.
Can cis and trans isomers interconvert by rotation around the double bond?
A: No, they cannot interconvert by rotation because breaking the π bond is required.
What are the conformations of butane that interconvert by rotation?
A: Anti conformation and eclipsed conformation.
How does restricted rotation in alkenes contribute to stereoisomerism?
A: It allows for distinct cis and trans isomers, which are stereoisomers with different spatial arrangements.
Which isomer, cis or trans, generally has a lower boiling point and why?
A: Trans isomers have a lower boiling point due to their more symmetric structure, which leads to weaker intermolecular forces.
What type of molecular orbital interaction must remain intact to maintain a double bond?
A: The side-by-side overlap of the p orbitals forming the pi bond.
How can cis and trans isomers be converted into one another?
A: Cis and trans isomers can only interconvert if the double bond is broken, such as through a chemical reaction.
