Question 1

Which of the following statements best explains why cycloalkanes have the general formula $$\mathrm{C}_n\mathrm{H}_{2n}$$, while acyclic alkanes have the formula $$\mathrm{C}_n\mathrm{H}_{2n+2}$$?

Accepted Answer

Cycloalkanes form rings, causing two fewer hydrogens due to the ring closure.

Question 2

Which of the following is a constitutional isomer of butane ($$\mathrm{C}_4\mathrm{H}_{10}$$)?

Accepted Answer

2-methylpropane

Question 3

What is the correct IUPAC name for the following structure?

A chain of 8 carbons with methyl groups at C2 and C6, and an ethyl group at C5.

Accepted Answer

5-ethyl-2,6-dimethyloctane

Question 4

Which of the following best describes the difference between staggered and eclipsed conformations in ethane?

Accepted Answer

Staggered conformations have a dihedral angle of $$60^\circ$$, while eclipsed conformations have a dihedral angle of $$0^\circ.$$

Question 5

Which factor most significantly increases the boiling point of an alkane?

Accepted Answer

Increasing the number of carbons in the molecule

Question 6

A student draws a Newman projection of butane looking down the C2–C3 bond. Which conformation is lowest in energy?

Accepted Answer

Anti conformation with methyl groups $$180^\circ$$ apart

Question 7

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

Accepted Answer

The chair conformation eliminates both angle and torsional strain.

Question 8

Which of the following is true regarding the ring-flip of cyclohexane?

Accepted Answer

Axial hydrogens become equatorial and vice versa.

Question 9

A substituted cyclohexane has a tert-butyl group and a methyl group. Which conformation is most stable?

Accepted Answer

Tert-butyl equatorial, methyl axial

Question 10

Which of the following statements about the combustion of alkanes is correct?

Accepted Answer

Combustion converts all C–H and C–C bonds to C–O bonds.

Question 11

Which of the following best describes a cis-1,4-dimethylcyclohexane?

Accepted Answer

Both methyl groups are on the same side of the ring.

Question 12

Which of the following is the correct IUPAC name for a cycloalkane with two methyl groups at C1 and C3?

Accepted Answer

1,3-dimethylcyclohexane

Question 13

Which of the following best explains why branching lowers the boiling point of alkanes?

Accepted Answer

Branching decreases the surface area, reducing van der Waals interactions.

Question 14

Which of the following is a correct statement about the solubility of alkanes?

Accepted Answer

Alkanes are soluble in organic solvents and insoluble in water.

Question 15

Which of the following is the correct IUPAC name for a cycloalkane with an ethyl group at C1 and a methyl group at C3?

Accepted Answer

1-ethyl-3-methylcyclohexane

Question 16

Which of the following best describes the effect of a large substituent, such as tert-butyl, on the equilibrium of cyclohexane chair conformations?

Accepted Answer

It anchors the ring in the conformation where the tert-butyl group is equatorial.

Question 17

Which of the following is true about the energy difference between staggered and eclipsed conformations of ethane?

Accepted Answer

The energy difference is approximately $$3\ \mathrm{kcal/mol}$$, with each eclipsed C–H bond contributing $$1\ \mathrm{kcal/mol}.$$

Question 18

Which of the following best describes the process of refining crude oil?

Accepted Answer

It separates crude oil into fractions based on boiling point.

Question 19

Which of the following is a correct statement about the nomenclature of alkanes?

Accepted Answer

The parent chain is the longest continuous chain of carbons, regardless of bends.

Chapter 4: Alkanes and Cycloalkanes: Structure, Nomenclature, Properties, and Conformations

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