Module 7: Alkene Structure and Reactivity

Question 1

When is cis-trans isomerism possible?

Answer 1

If the pair of substituents on each side of the double bond are different

Question 2

What are z isomers?

Answer 2

Molecules which have higher ranked groups on the same side of the double bond

Question 3

What are e isomers?

Answer 3

Molecules which have higher-ranked groups are on opposite sides of the double bond

Question 4

Why would an alkene be unsaturated?

Answer 4

Alkene has less hydrogen bonds than alkanes

Question 5

How does the number of substituents affect alkene stability?

Answer 5

More substituted alkenes are more stable

Question 6

How does heat relate to the stability of alkene?

Answer 6

More stable compounds give off less heat when reacted with H2. Therefore, more substituted alkenes release heat and therefore more stable

Question 7

What makes an alkyl halide?

Answer 7

Alkene reacting with a hydrogen bonded to halogen

Question 8

Describe the mechanism of how an alkyl halide is formed

Answer 8

1. Alkene acts as a nucleophile and grabs the H of the HX.
2. This pushes the electron to the halogen, creating a halogen anion and an a carbocation on the alkene.
3. The halogen anion will acts as a nucleophile and will initiate a bond with the electrophile carbocation.

Question 9

What is regiospecific?

Answer 9

Reaction in which only one of two possible orientations of an addition occur

Question 10

In an addition of HX to an alkene, why would the halogen attach to the carbon with the more alkyl substituents and the hydrogen attach to the carbon with less alkyl subsitituents?

Answer 10

This ensures that the intermediate is the most stable

Question 11

How does inductive affect contribute to carbocation stability?

Answer 11

Highly substituents carbocations are more stable than less substituents

Question 12

What is hyperconjugation?

Answer 12

Stabilizing interaction from the electrons of a sigma bond with an adjacent empty or partially filled p orbital or a pi orbital

Question 13

What is a hydride shift?

Answer 13

Shift of a hydrogen atom and its electron pair between neighboring carbons

Question 14

What is an alkyl shift?

Answer 14

Shift of an alkyl group and its electron pair between neighboring carbon

Question 15

Why do carbocation rearrangement occur?

Answer 15

Alkyl and hydride shift occur to make a more stable carbocation