Question

True or false:

a) The cis- and trans-alkene isomers can inter-convert into each other by C=C (carbon double bond) bond rotation.

b) Cyclobutane has HIGHER Heat of Combustion than Cyclohexane

c) For 4,4-dimethlycyclooctene, the cis-isomers is MORE STABLE than the trans-isomer

d) Due to hydrogen bonding interaction, ethanol has LOWER boiling point than fluoroethane

e) Secondary alcohols are LESS REACTIVE than tertiary alcohols for acid-catalyzed dehydration.

Answer 1

a) False

Carbon carbon double bond roatation will break the bond, only carbon carbon single bond roatation is possible. The double bond consists of a sigma & Pi bond, the Pi bond is formed by the lateral overlap of the P orbitals. This overlap will break if the bond is rotated.

b) False

As the carbon chain increases the heat of combustion increses. Increase in size of molecule increases Van der Waals attractions forces within the molecule so they become harder to ignite.

c) True

The cis isomer have less ring strain so this is more stable than the trans isomer.

d) False

Due to hydrogen bonding present in ethanol ethanol has higher boiling point than fluoroethane

e) True

Tertiary alochols form the tertiary carbocation which is more stable than the secondary carbocation formed by the secondary alochols by dehydration catalyzed by acids.