Question 1

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

Accepted Answer

Larger alkanes have more surface area, leading to stronger van der Waals forces.

Question 2

What is the IUPAC name for the following compound?

$$\mathrm{CH_3CH_2CH(CH_3$)CH_2CH_3}$$

Accepted Answer

3-methylpentane

Question 3

Which of the following is a correct statement about constitutional isomers?

Accepted Answer

They have the same molecular formula but different connectivity of atoms.

Question 4

A student is asked to draw all possible constitutional isomers of $$\mathrm{C_5H_{12}}. $$Which of the following is NOT a correct isomer?

Accepted Answer

2,3-dimethylpropane

Question 5

Which of the following best describes the difference between the anti and gauche conformations of butane?

Accepted Answer

In the anti conformation, the two methyl groups are $$180^\circ$$ apart; in the gauche, they are $$60^\circ$$ apart.

Question 6

Which of the following cycloalkanes has the greatest angle strain?

Accepted Answer

Cyclopropane

Question 7

A molecule of methylcyclohexane is most stable when the methyl group is in which position?

Accepted Answer

Equatorial

Question 8

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 eclipsing interactions and bond angles of $$109.5^\circ.$$

Question 9

What is the correct IUPAC name for the following structure?

$$\mathrm{CH_3CH_2CH(CH_3$)CH_2CH_2CH_3}$$

Accepted Answer

3-methylhexane

Question 10

Which of the following statements about cyclopropane is TRUE?

Accepted Answer

Cyclopropane has significant angle strain because its bond angles are $$60^\circ.$$

Question 11

Which of the following is the correct systematic name for a compound with a ten-carbon chain and a tert-butyl group on carbon 5?

Accepted Answer

5-tert-butyldecane

Question 12

A sample of 1,3-dimethylcyclohexane is found to be almost entirely in one conformation at room temperature. Which conformation is this, and why?

Accepted Answer

Diequatorial, because both methyl groups avoid the axial position and 1,3-diaxial interactions.

Question 13

Which of the following best describes a Newman projection?

Accepted Answer

A way to visualize the conformation of a molecule by looking down a specific carbon–carbon bond.

Question 14

Which of the following is a correct statement about the stability of cis- and trans-1,2-dimethylcyclohexane?

Accepted Answer

Both conformations of the cis isomer have one methyl axial and one equatorial, so they have the same energy.

Question 15

Which of the following is the correct molecular formula for a cycloalkane with 7 carbon atoms?

Accepted Answer

$$\mathrm{C_7H_{14}}$$

Question 16

A compound is named 4-ethyl-2-methylhexane. Which of the following is true about the order of substituents in the name?

Accepted Answer

Substituents are listed in alphabetical order, ignoring numerical prefixes.

Question 17

Which of the following best explains why cyclopentane adopts a puckered (envelope) conformation?

Accepted Answer

To reduce torsional strain from eclipsing interactions.

Question 18

Which of the following is the general formula for an unbranched alkane?

Accepted Answer

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

Question 19

Which of the following is a correct statement about the 1,3-diaxial interaction in cyclohexane derivatives?

Accepted Answer

It is a steric interaction between an axial substituent and axial hydrogens on carbons 3 and 5.

Chapter 3: Structure and Stereochemistry of Alkanes – Study Notes

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