Intermolecular Forces and Stability

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Organic Chemistry › Intermolecular Forces and Stability

Questions 1 - 10
1

Which of the following compounds is a saturated hydrocarbon?

Propane

Propene

Propyne

Benzene

Explanation

By definition, a saturated hydrocarbon is a compound that contains no double or triple bonds-all single bonds. Of these choices, propane (-ane suffix indicates that it is an alkane, which contains only single bonds) is the only saturated hydrocarbon.

2

Which of the following compounds is a saturated hydrocarbon?

Propane

Propene

Propyne

Benzene

Explanation

By definition, a saturated hydrocarbon is a compound that contains no double or triple bonds-all single bonds. Of these choices, propane (-ane suffix indicates that it is an alkane, which contains only single bonds) is the only saturated hydrocarbon.

3

Which of the following is the mostsoluble in hexane?

Carbon tetrachloride

Ethanol

Water

Phenylacetic acid

Explanation

When discussing solubility, remember the phrase, "like dissolves like."

Hexane, being made of solely carbons and hydrogens, is extremely nonpolar. Thus, our correct answer must also be nonpolar, as like dissolves like. Although carbon tetrachloride is made up of four polar bonds, the net charge on the molecule is zero, as the polar bonds all pull in equal and opposite directions. All other answer choices are polar, and thus insoluble in hexane.

4

Which of the following is the mostsoluble in hexane?

Carbon tetrachloride

Ethanol

Water

Phenylacetic acid

Explanation

When discussing solubility, remember the phrase, "like dissolves like."

Hexane, being made of solely carbons and hydrogens, is extremely nonpolar. Thus, our correct answer must also be nonpolar, as like dissolves like. Although carbon tetrachloride is made up of four polar bonds, the net charge on the molecule is zero, as the polar bonds all pull in equal and opposite directions. All other answer choices are polar, and thus insoluble in hexane.

5

Which of the following statements is true of alkynes?

Internal alkynes are more stable than terminal alkynes

Terminal alkynes are less acidic than internal alkynes

Alkynes are very soluble in water

The triple bond of an alkyne consists of three pi-bonds

Terminal alkynes are stronger compounds than internal alkynes

Explanation

The answer is "Internal alkynes are more stable than terminal alkynes" as it is the only true statement in regards to alkynes. Internal alkynes are more stable because they have a better conjugated system than terminal alkynes. A conjugated system is a system of a single bond, then a multiple bond, then a single bond, and so on. A conjugated system will always be more stable than an unconjugated system. It is evident that the internal alkyne follows the conjugated system and the terminal alkyne does not based on the picture below.

1

6

Which of the following statements is true of alkynes?

Internal alkynes are more stable than terminal alkynes

Terminal alkynes are less acidic than internal alkynes

Alkynes are very soluble in water

The triple bond of an alkyne consists of three pi-bonds

Terminal alkynes are stronger compounds than internal alkynes

Explanation

The answer is "Internal alkynes are more stable than terminal alkynes" as it is the only true statement in regards to alkynes. Internal alkynes are more stable because they have a better conjugated system than terminal alkynes. A conjugated system is a system of a single bond, then a multiple bond, then a single bond, and so on. A conjugated system will always be more stable than an unconjugated system. It is evident that the internal alkyne follows the conjugated system and the terminal alkyne does not based on the picture below.

1

7

How many sigma and pi bonds does a triple bond contain?

and

and

and

and

and

Explanation

A triple bond contains 2 pi bonds and a single sigma bond.

8

How many sigma and pi bonds does a triple bond contain?

and

and

and

and

and

Explanation

A triple bond contains 2 pi bonds and a single sigma bond.

9

Which compound has the greatest dipole moment?

Explanation

The dipole moment refers to the difference in electronegativity between two atoms in a molecule. The greatest electronegativity difference results in the largest dipole moment. The trend for electronegativity increases as you move up and to the right on the periodic table. Moving to the right increases electronegativity far more than moving up.

The answer will be a molecule with a halogen, as the halogens are particularly electronegative. This narrows our options to or . Bromine is farther up the halogen group than iodine, so bromine will be more electronegative and result in the larger dipole moment. The correct answer is .

10

Which compound has the greatest dipole moment?

Explanation

The dipole moment refers to the difference in electronegativity between two atoms in a molecule. The greatest electronegativity difference results in the largest dipole moment. The trend for electronegativity increases as you move up and to the right on the periodic table. Moving to the right increases electronegativity far more than moving up.

The answer will be a molecule with a halogen, as the halogens are particularly electronegative. This narrows our options to or . Bromine is farther up the halogen group than iodine, so bromine will be more electronegative and result in the larger dipole moment. The correct answer is .

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