Question 1

Which of the following statements best explains why branched alkanes generally have lower boiling points than their straight-chain isomers?

Accepted Answer

Branched alkanes have less surface area contact, resulting in weaker van der Waals forces.

Question 2

What is the general formula for saturated hydrocarbons (alkanes)?

Accepted Answer

$$\mathrm{C_nH_{2n+2}}$$

Question 3

Which conformation of ethane is the most stable and why?

Accepted Answer

Staggered, because the dihedral angle is $$60^\circ$$ and torsional strain is minimized.

Question 4

A molecule of cyclopropane has significant ring strain. Which type of strain is primarily responsible for this?

Accepted Answer

Angle strain due to deviation from the tetrahedral bond angle.

Question 5

Which of the following is the correct IUPAC name for a compound with a nine-carbon chain, an ethyl group at carbon 3, and a complex substituent (1-ethyl-2-methylpropyl) at carbon 5?

Accepted Answer

3-Ethyl-5-(1-ethyl-2-methylpropyl)nonane

Question 6

Which conformation of butane is the lowest in energy?

Accepted Answer

Anti ($$	heta = 180^\circ)$$

Question 7

What is the main reason for the higher melting points of branched alkanes compared to their straight-chain isomers?

Accepted Answer

Branched alkanes have more efficient packing in the crystalline state.

Question 8

Which of the following cycloalkanes would you expect to have the smallest heat of combustion per $$\mathrm{CH_2$}$$ group?

Accepted Answer

Cyclopentane

Question 9

In the chair conformation of cyclohexane, why is the equatorial position preferred for bulky substituents?

Accepted Answer

It minimizes 1,3-diaxial interactions, reducing steric strain.

Question 10

Which of the following is NOT a major use of alkanes?

Accepted Answer

Protein synthesis

Question 11

What is the primary functional group present in aromatic hydrocarbons?

Accepted Answer

Benzene ring

Question 12

Which of the following best describes the relationship between the number of carbon atoms in an alkane and its boiling point?

Accepted Answer

Boiling point increases as the number of carbon atoms increases.

Question 13

Which of the following is the correct IUPAC name for a cyclohexane ring with bromine atoms at carbons 1 and 4, both on the same side?

Accepted Answer

Cis-1,4-dibromocyclohexane

Question 14

Which of the following is a correct statement about the chair and boat conformations of cyclohexane?

Accepted Answer

The boat conformation suffers from torsional strain due to eclipsing interactions.

Question 15

Which of the following is the most stable conformation of cis-1-tert-butyl-4-methylcyclohexane?

Accepted Answer

The methyl group is axial and the tert-butyl group is equatorial.

Question 16

Which of the following is NOT a correct step in the IUPAC naming of alkanes?

Accepted Answer

Always use the chain with the fewest substituents if chains are equal length.

Question 17

Which of the following is a correct statement about the conformational analysis of ethane?

Accepted Answer

The energy difference between staggered and eclipsed conformations is about $$3.0$$ kcal/mol.

Question 18

Which of the following is the correct IUPAC name for a compound with a cyclopentane ring and two ethyl groups on the same carbon, plus a methyl group on another carbon?

Accepted Answer

1,1-Diethyl-3-methylcyclopentane

Question 19

Which of the following is a fused bicyclic system?

Accepted Answer

Bicyclo[4.4.0]decane

Structure and Stereochemistry of Alkanes

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