Q: Which of the following is the most stable conformation of butane when viewed down the C2–C3 bond?

Anti conformation ($$180^\\circ$$ between methyl groups)

Q: Which of the following best explains why cyclopropane is highly strained?

It has bond angles of $$60^\\circ$$ and both angle strain and torsional strain due to eclipsed bonds.

Question 1

Which of the following statements best explains why the boiling point of alkanes increases as the number of carbon atoms increases?

Accepted Answer

The increased number of carbon atoms increases the surface area, leading to stronger van der Waals (dispersion) forces.

Question 2

Which of the following is the correct IUPAC name for the compound $$(CH_3CH_2CH_2)_2CH$$?

Accepted Answer

3-Ethyl-2-methylpentane

Question 3

Which of the following best describes constitutional isomers?

Accepted Answer

Compounds with the same molecular formula but different connectivity of atoms.

Question 4

A student is asked to name the following compound: $$CH_3CH_2CH(CH_3$)CH_2CH_3. $$What is the correct IUPAC name?

Accepted Answer

3-Methylpentane

Question 5

Which of the following is the most stable conformation of butane when viewed down the C2–C3 bond?

Accepted Answer

Anti conformation ($$180^\circ$$ between methyl groups)

Question 6

Which of the following best explains why cyclopropane is highly strained?

Accepted Answer

It has bond angles of $$60^\circ$$ and both angle strain and torsional strain due to eclipsed bonds.

Question 7

Which of the following is the correct IUPAC name for a cycloalkane with a five-membered ring and an ethyl and a methyl group on adjacent carbons?

Accepted Answer

1-Ethyl-2-methylcyclopentane

Question 8

Which of the following statements about the chair conformation of cyclohexane is TRUE?

Accepted Answer

It is the most stable conformation because it has no angle or torsional strain.

Question 9

A molecule of 1,3-dimethylcyclohexane is found to have both methyl groups in equatorial positions. Which isomer is this and why is this conformation favored?

Accepted Answer

Cis isomer; both groups are on the same side and equatorial positions minimize 1,3-diaxial interactions.

Question 10

Which of the following best describes a 1,3-diaxial interaction in substituted cyclohexanes?

Accepted Answer

A repulsive interaction between an axial substituent on carbon 1 and axial hydrogens on carbons 3 and 5.

Question 11

Which of the following is the correct IUPAC name for the compound with the following structure: a six-carbon chain with a methyl group on carbon 2 and an ethyl group on carbon 4?

Accepted Answer

4-Ethyl-2-methylhexane

Question 12

Which of the following statements about the physical properties of cycloalkanes is correct?

Accepted Answer

Cycloalkanes are nonpolar and relatively inert.

Question 13

Which of the following best describes the difference between a staggered and an eclipsed conformation in ethane?

Accepted Answer

In the staggered conformation, the dihedral angle between adjacent C-H bonds is $$60^\circ$$, minimizing torsional strain.

Question 14

A student is analyzing the melting points of alkanes and notices that alkanes with even numbers of carbons have higher melting points than those with odd numbers. What is the most likely explanation?

Accepted Answer

Even-numbered alkanes pack more efficiently in the solid state, leading to higher melting points.

Question 15

Which of the following is a correct statement about the nomenclature of cycloalkanes with multiple substituents?

Accepted Answer

Number the ring to give all substituents the lowest possible numbers.

Question 16

Which of the following best describes the relationship between n-butane and isobutane?

Accepted Answer

They are constitutional isomers.

Question 17

Which of the following is the correct general formula for an acyclic alkane?

Accepted Answer

$$C_nH_{2n+2}$$

Question 18

Which of the following best explains why the chair conformation of cyclohexane is more stable than the boat conformation?

Accepted Answer

The chair conformation has no angle or torsional strain, while the boat conformation has both.

Question 19

A molecule of 2,3-dimethylbutane is rotated about the C2–C3 bond. Which Newman projection represents its most stable conformation?

Accepted Answer

Both methyl groups are anti to each other.

Structure and Stereochemistry of Alkanes: Study Notes

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