Question

Question #d30a7

Answer 1

You find N by identifying the non-equivalent sets of hydrogen atoms, and M by considering the shapes of the molecules. There are N = 4 isomers and M = 3 fractions.

Explanation:

WARNING: Long answer.

Number of Isomers N

The structure of 2-methylbutane is

There are four different sets of equivalent hydrogens:

• 1 The three H atoms on C-4
• 2 The two H atoms on C-3
• 3 The one H atom on C-2
• 4 The six H atoms on C-3 and the methyl substituent

So there are four possible monochloro substitution products:

1: 1-Chloro-3-methylpentane

2: 2-Chloro-3-methylpentane

3: 2-Chloro-2-methylpentane

4: 1-Chloro-2-methylpentane

Number of fractions, M

3 has four groups attached to the same carbon atom.

The molecules will have a roughly spherical shape.

They will have little contact with each other and therefore small dipole-dipole and London dispersion forces.

They will have the lowest boiling point.

2 has a chain of four atoms with groups on two different carbon atoms.

The molecules should have better contact with each other and therefore stronger dipole-dipole and London dispersion forces.

2 will have a higher boiling point than 3.

1 and 4 each have a chain if five atoms with only one substituent.

The molecules should have the best contact with each other and therefore the strongest dipole-dipole and London dispersion forces.

1 and 4 should have the highest boiling points, and they should not differ much from each other.

Prediction:

• The lowest boiling Fraction 1 contains 3.
• Fraction 2 contains 2.
• The highest boiling Fraction 3 contains 1 and 4.