Question 1

Which statement best describes the bonding in an alkene?

Accepted Answer

Alkenes consist of two adjacent sp2-hybridized carbons, with their remaining p orbitals overlapping sideways to form a pi bond.

Question 2

What is the main type of reaction that alkenes undergo?

Accepted Answer

Addition reactions

Question 3

During the electrophilic addition of HBr to an alkene, what is the rate-determining step?

Accepted Answer

The formation of the carbocation intermediate by nucleophilic attack of the pi electrons on HBr

Question 4

Which species acts as the electrophile in the addition of HBr to an alkene?

Accepted Answer

H+

Question 5

What is the product of the following reaction? $$\mathrm{CH_2$=CH_2$ + HBr \rightarrow}$$

Accepted Answer

$$\mathrm{CH_3CH_2Br}$$

Question 6

Why are alkyl groups stabilizing to alkenes?

Accepted Answer

Alkyl groups donate electron density to the double bond, stabilizing the pi electrons.

Question 7

Which alkene is expected to be the most stable?

Accepted Answer

A tetrasubstituted alkene

Question 8

Consider the catalytic hydrogenation of 2-methyl-2-butene, 2-methyl-1-butene, and 3-methyl-1-butene. Which compound releases the least heat upon hydrogenation?

Accepted Answer

2-methyl-2-butene

Question 9

Which statement best explains why trans-2-butene is more stable than cis-2-butene?

Accepted Answer

Trans-2-butene has less steric strain between substituents than cis-2-butene.

Question 10

Rank the following compounds in order of decreasing stability: trans-3-hexene, cis-3-hexene, cis-2,5-dimethyl-3-hexene, and cis-3,4-dimethyl-3-hexene.

Accepted Answer

cis-3,4-dimethyl-3-hexene \u003e cis-2,5-dimethyl-3-hexene \u003e trans-3-hexene \u003e cis-3-hexene

Question 11

Which of the following best describes the role of a metal catalyst in catalytic hydrogenation of alkenes?

Accepted Answer

It provides a surface for the alkene and hydrogen to adsorb, facilitating bond formation.

Question 12

Which of the following is true about the reaction coordinate diagram for the addition of HBr to an alkene?

Accepted Answer

The first step has the highest activation energy and is the rate-determining step.

Question 13

In the mechanism of electrophilic addition to an alkene, what is the intermediate formed after the first step?

Accepted Answer

A carbocation

Question 14

Which of the following best explains why addition reactions of alkenes are usually exothermic?

Accepted Answer

Two new sigma bonds are formed, which are stronger than the pi bond that is broken.

Question 15

Which of the following curved arrow conventions is correct for the first step of electrophilic addition of HBr to propene?

Accepted Answer

Arrow from the pi bond of the alkene to the hydrogen atom of HBr.

Question 16

Which of the following statements about transition states in the addition of HBr to an alkene is correct?

Accepted Answer

Transition states involve bonds that are partially broken or formed.

Question 17

Which of the following is a correct representation of the catalytic hydrogenation of 2-butene?

Accepted Answer

$$\mathrm{CH_3CH=$$CHCH_3$$ + H_2$ \xrightarrow{Pd/C} CH_3CH_2CH_2CH_3}$$

Chapter 5: Alkenes – Introduction to Reactivity and Stability

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