Question 1

Which of the following statements best explains why alkenes are considered unsaturated hydrocarbons?

Accepted Answer

Alkenes have fewer hydrogen atoms than alkanes with the same number of carbons due to the presence of double bonds.

Question 2

What is the bond dissociation energy (BDE) of a carbon-carbon double bond ($$C=C) in $$alkenes?

Accepted Answer

$$63$$ kcal/mol

Question 3

Why is there no free rotation around the double bond in alkenes?

Accepted Answer

Because the $$	ext{p}$$ orbitals overlap to form a $$	ext{π}$$ bond, which restricts rotation.

Question 4

Which of the following is the correct IUPAC name for the compound $$CH_2=CH$$-$$CH_2$$-$$CH_3$$?

Accepted Answer

1-butene

Question 5

How many degrees of unsaturation are present in cyclohexene?

Accepted Answer

2

Question 6

Which statement about cis-trans isomerism in alkenes is correct?

Accepted Answer

Cis isomers have similar groups on the same side of the double bond.

Question 7

According to the Cahn-Ingold-Prelog rules, what determines the priority of groups attached to the double bond in E/Z nomenclature?

Accepted Answer

The atomic number of the atoms directly attached to the double bond.

Question 8

Which of the following is a correct example of an alkene as a substituent?

Accepted Answer

Methylidene group ($$=CH_2$)

Question 9

Which of the following alkenes would release the most heat upon hydrogenation?

Accepted Answer

A monosubstituted alkene

Question 10

What is the Saytzeff rule in alkene synthesis?

Accepted Answer

The major product is the most substituted alkene.

Question 11

Which base would favor the formation of the Hofmann product in an E2 elimination?

Accepted Answer

A bulky base like tert-butoxide ($$tBuO^-)$$

Question 12

Why are trans isomers of alkenes generally more stable than cis isomers?

Accepted Answer

Trans isomers have less steric hindrance between substituents.

Question 13

Which of the following statements about cycloalkenes is correct?

Accepted Answer

Cyclooctene is the smallest cycloalkene that can exist as a trans isomer.

Question 14

In an E2 elimination reaction, what is the stereochemical requirement for the leaving group and the hydrogen being abstracted?

Accepted Answer

They must be anti-coplanar.

Question 15

Which of the following is a correct mechanism for the acid-catalyzed dehydration of alcohols to form alkenes?

Accepted Answer

Protonation of the hydroxyl group, followed by loss of water and formation of a carbocation, then deprotonation to form the alkene.

Question 16

Which of the following best describes the effect of alkyl substitution on alkene stability?

Accepted Answer

Alkyl groups stabilize the double bond by donating electrons.

Question 17

Which product is favored when a bulky base is used in the dehydrohalogenation of a 2° alkyl halide?

Accepted Answer

The Hofmann product (least substituted alkene)

Question 18

What is the major product when 2-bromobutane undergoes E2 elimination with potassium tert-butoxide?

Accepted Answer

1-butene

Question 19

Which of the following is true about the heat of hydrogenation of alkenes?

Accepted Answer

The less substituted the alkene, the higher the heat of hydrogenation.

Question 20

Which of the following is the correct IUPAC name for the compound with the structure $$CH_2=CH$$-$$CH_2-CH$$=$$CH_2$$?

Accepted Answer

1,3-pentadiene

Structure and Synthesis of Alkenes: Chapter 7 Study Notes

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