Question 1

Which of the following statements best explains why the trans (E) isomer of 2-butene is more stable than the cis (Z) isomer?

Accepted Answer

The trans isomer has less steric hindrance between substituents on opposite sides of the double bond.

Question 2

Which of the following best describes the bonding in an alkene double bond?

Accepted Answer

One $$\sigma$$ bond formed by head-on overlap of $$sp^2$$ orbitals and one $$\pi$$ bond formed by side-on overlap of $$2p$$ orbitals.

Question 3

A chemist measures the heat of hydrogenation ($$\Delta H) $$for three butene isomers. Which isomer is expected to have the most negative $$\Delta H$$ value?

Accepted Answer

1-butene (terminal alkene)

Question 4

According to the general order of alkene stability, which of the following is the most stable?

Accepted Answer

A tetrasubstituted alkene

Question 5

Which rule predicts that elimination with a bulky base will favor the formation of the less substituted (terminal) alkene?

Accepted Answer

Hofmann Rule

Question 6

In an E2 elimination using a small, unhindered base, which product is favored and why?

Accepted Answer

The more substituted, internal alkene is favored due to its greater thermodynamic stability.

Question 7

Which of the following statements about the $$\pi$$ bond in alkenes is correct?

Accepted Answer

The $$\pi$$ bond is weaker than the $$\sigma$$ bond and is responsible for the reactivity of alkenes.

Question 8

A student is asked to assign E/Z configuration to an alkene. What is the correct first step?

Accepted Answer

Assign priorities to the groups attached to each $$sp^2$$ carbon using the Cahn-Ingold-Prelog rules.

Question 9

Which of the following best explains why internal alkenes are generally more stable than terminal alkenes?

Accepted Answer

Internal alkenes benefit from greater hyperconjugation and alkyl substitution.

Question 10

During an E2 elimination, which geometric relationship between the leaving group and the hydrogen being removed is required for the reaction to proceed efficiently?

Accepted Answer

Anti-coplanar (180° dihedral angle)

Question 11

A chemist uses potassium tert-butoxide (a bulky base) in an E2 elimination of 2-bromo-2-methylbutane. Which product will be favored?

Accepted Answer

The less substituted, terminal alkene (Hofmann product)

Question 12

Which of the following is NOT a reason why the cis isomer of an alkene is less stable than the trans isomer?

Accepted Answer

Cis isomers are stabilized by intramolecular hydrogen bonding.

Question 13

Which experimental method is commonly used to compare the relative stabilities of alkene isomers?

Accepted Answer

Measuring the heat of hydrogenation ($$\Delta H) $$for each isomer.

Question 14

Which of the following best describes the stereospecificity of the E2 reaction?

Accepted Answer

Each diastereomer of the starting material gives only one stereoisomer of the alkene product.

Question 15

A student is asked to draw the Newman projection for an E2 elimination. What key feature must be present for the reaction to occur?

Accepted Answer

The leaving group and the hydrogen being abstracted must be anti to each other.

Question 16

Which of the following statements about the transition state in a Saytzev E2 elimination is correct?

Accepted Answer

The transition state leading to the more substituted alkene is lower in energy.

Question 17

Which of the following best explains why a bulky base favors the Hofmann product in E2 elimination?

Accepted Answer

Bulky bases have difficulty accessing hindered hydrogens, so they abstract more accessible primary hydrogens.

Question 18

Which of the following is the correct order of alkene stability from least to most stable?

Accepted Answer

$$\mathrm{CH_2$=CH_2$} \u003c \mathrm{RCH=CH_2$} \u003c \mathrm{RCH=CHR\ (cis)} \u003c \mathrm{RCH=CHR\ (trans)} \u003c $$ trisubstituted $$\u003c$$ tetrasubstituted

Question 19

Which of the following best describes the effect of hyperconjugation on alkene stability?

Accepted Answer

Hyperconjugation stabilizes alkenes by delocalizing electrons from adjacent C-H bonds into the $$\pi$$ system.

Alkenes: Structure and Synthesis – Key Concepts and Mechanisms

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