Question 1

Which of the following statements best describes a functional group in organic chemistry?

Accepted Answer

A collection of atoms at a site that have a characteristic behavior in all molecules where they occur, generally reacting in a typical way independent of the rest of the molecule.

Question 2

What is the molecular formula for a straight-chain alkane with 8 carbon atoms?

Accepted Answer

$$\mathrm{C_8H_{18}}$$

Question 3

Which of the following is a constitutional isomer of pentane ($$\mathrm{C_5H_{12}}$$)?

Accepted Answer

2-methylbutane

Question 4

A student is asked to draw all possible isomers of butane ($$\mathrm{C_4H_{10}}). $$Which structures should they include?

Accepted Answer

n-butane and isobutane (2-methylpropane)

Question 5

Which of the following best describes the difference between a straight-chain alkane and a branched-chain alkane?

Accepted Answer

A straight-chain alkane has all carbons connected to no more than two other carbons, while a branched-chain alkane has at least one carbon connected to three or four other carbons.

Question 6

Which of the following is the correct IUPAC name for the compound with the condensed formula $$\mathrm{CH_3CH_2CH(CH_3$)CH_2CH_3}$$?

Accepted Answer

3-methylpentane

Question 7

When naming alkanes, what is the correct order of steps according to IUPAC rules?

Accepted Answer

Find the longest hydrocarbon chain, number the atoms in the chain, identify and number substituents, write the name as a single word.

Question 8

Which of the following Newman projections represents the most stable conformation of ethane?

Accepted Answer

Staggered conformation, where all C-H bonds on the front carbon are as far as possible from those on the back carbon ($$60^\circ$$ dihedral angle).

Question 9

Which of the following best explains why the eclipsed conformation of ethane is higher in energy than the staggered conformation?

Accepted Answer

There is increased electron repulsion between the aligned C-H bonds in the eclipsed conformation.

Question 10

A molecule of 2,3-dimethylbutane is viewed along the C2–C3 bond. Which conformation is most stable?

Accepted Answer

The staggered conformation with the two methyl groups as far apart as possible (anti conformation).

Question 11

Which of the following is the correct condensed structural formula for isobutane?

Accepted Answer

$$\mathrm{(CH_3$)_3CH}$$

Question 12

Which of the following statements about alkyl groups is correct?

Accepted Answer

An alkyl group is formed by removing one hydrogen atom from an alkane.

Question 13

Which of the following is the correct IUPAC name for a molecule with the structure $$\mathrm{CH_3CH_2CH_2CH_2CH_3}$$?

Accepted Answer

Pentane

Question 14

A hydrocarbon is found to have the formula $$\mathrm{C_7H_{16}}. $$How many rings or double bonds does it contain?

Accepted Answer

None; it is a saturated alkane.

Question 15

Which of the following best describes a tertiary carbon atom?

Accepted Answer

A carbon atom bonded to three other carbon atoms.

Question 16

Which of the following is the correct name for a molecule with the structure $$\mathrm{CH_3CH_2CH(CH_3$)CH_2CH_2CH_3}$$?

Accepted Answer

3-methylhexane

Question 17

Which of the following best describes the anti conformation in butane as seen in a Newman projection?

Accepted Answer

The two methyl groups are $$180^\circ$$ apart.

Question 18

A student is asked to name a molecule with two ethyl groups attached to a hexane chain at carbons 3 and 4. What is the correct IUPAC name?

Accepted Answer

3,4-diethylhexane

Question 19

Which of the following is a correct statement about the energy barrier to rotation around a C–C single bond in alkanes?

Accepted Answer

There is a small energy barrier due to torsional strain, making some conformations more stable than others.

Organic Compounds: Alkanes and Their Stereochemistry – Study Notes

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