Question

For each of the following compounds,

1. Draw the Lewis structure.
2. Show how the bond dipole moments (and those of any nonbonding pairs of electrons) contribute to the molecular dipole moment.
3. Estimate whether the compound will have a large, small, or zero dipole moment.

(a) ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}\mathbf{CH}\mathbf{=}\mathbf{N}\mathbf{-}{\mathbf{CH}}_{\mathbf{3}}$

(b) ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$

(c) ${\mathbf{CBr}}_{\mathbf{4}}$

(d)

Structure (d)

(e)

Structure (e)

(f)

Structure (f)

(g)

Structure (g)

(h)

Structure (h)

Short answer

(a)

1.

Lewis structure of structure (a)

2.

Dipole moment in Structure (a)

3.Large dipole moment

(b)

1.

Lewis structure of structure (b)

2.

Dipole moment in Structure (b)

3.

Large dipole moment

(c)

1.

Lewis structure of structure (c)

2.

Dipole moment in Structure (c)

3.

Zero dipole moment.

(d)

1.

Lewis structure of structure (d)

2.

Dipole moment in Structure (d)

3.

Large dipole moment

(e)

1.

Lewis structure of structure (e)

2.

Dipole moment in Structure (e)

3.

Zero dipole moment

(f)

1.

Lewis structure of structure (f)

2.

Dipole moment in Structure (f)

3.

Moderate dipole moment

(g)

1.

Lewis structure of structure (g)

2.

Dipole moment in Structure (g)

3.

Moderate dipole moment

(h)

1.

Lewis structure of structure (h)

2.

Dipole moment in Structure (h)

3.

Large dipole moment

Step-by-step solution

Concept of Lewis structure

Lewis structures show the bonding between atoms in a molecule, as well as any lone pairs of electrons that may be present.A Lewis structure can represent any covalently attached molecule, as well as coordination compounds. When two electrical charges of identical magnitude but opposite signs are separated by a distance, the dipole moment is formed.

Lewis structure and dipole moment of structure (a)

The Lewis structure of given compound is as follows:

Lewis structure of structure (a)

The direction of dipole moment is from less electronegative element to more electronegative element.

The dipole moment in the given compound is as follows:

Dipole moment in Structure (a)

Nitrogen is more electronegative than carbon. Therefore, the direction of dipole moment of carbon nitrogen bond is towards nitrogen. The net dipole moment is towards the lone pair of nitrogen. Therefore, the total dipole moment is large.

Lewis structure and dipole moment of structure (b)

The Lewis structure of given compound is as follows:

Lewis structure of structure (b)

The direction of dipole moment is from less electronegative element to more electronegative element.

The dipole moment in the given compound is as follows:

Dipole moment in Structure (b)

Oxygen is more electronegative than carbon and hydrogen. Therefore, the direction of dipole moment of carbon-oxygen bond and carbon-hydrogen bond is towards nitrogen. The net dipole moment is towards the lone pair of nitrogen. Therefore, the total dipole moment is large.

Lewis structure and dipole moment of structure (c)

The Lewis structure of given compound is as follows:

Lewis structure of structure (c)

The direction of dipole moment is from less electronegative element to more electronegative element.

The dipole moment in the given compound is as follows:

Dipole moment in Structure (c)

Bromine is more electronegative than carbon. Therefore, the direction of dipole moment of carbon-bromine bond is towards bromine. The total dipole moment is in four opposite different directions and they cancel out each other. Therefore, the total dipole moment is zero.

Lewis structure and dipole moment of structure (d)

The Lewis structure of given compound is as follows:

Lewis structure of structure (d)

The direction of dipole moment is from less electronegative element to more electronegative element.

The dipole moment in the given compound is as follows:

Dipole moment in Structure (d)

Oxygen is more electronegative than carbon. Therefore, the direction of dipole moment of carbon-oxygen bond is towards nitrogen. The direction of dipole moment is upward direction. Therefore, the total dipole moment is large.

Lewis structure and dipole moment of structure (e)

The Lewis structure of given compound is as follows:

Lewis structure of structure (e)

The direction of dipole moment is from less electronegative element to more electronegative element.

The dipole moment in the given compound is as follows:

Dipole moment in Structure (e)

Nitrogen is more electronegative than carbon. Therefore, the direction of dipole moment of carbon-nitrogen bond is towards nitrogen. The total dipole moment is in four different directions and they cancel out each other. Therefore, the total dipole moment is zero.

Lewis structure and dipole moment of structure (f)

The Lewis structure of given compound is as follows:

Lewis structure of structure (f)

The direction of dipole moment is from less electronegative element to more electronegative element.

The dipole moment in the given compound is as follows:

Dipole moment in Structure (f)

Nitrogen is more electronegative than carbon. Therefore, the direction of dipole moment of carbon-nitrogen bond is towards nitrogen. The total dipole moment is in upward directions. Therefore, the total dipole moment is moderate.

Lewis structure and dipole moment of structure (g)

The Lewis structure of given compound is as follows:

Lewis structure of structure (g)

The direction of dipole moment is from less electronegative element to more electronegative element.

The dipole moment in the given compound is as follows:

Dipole moment in Structure (g)

Chlorine is more electronegative than carbon. Therefore, the direction of dipole moment of carbon-chlorine bond is towards chlorine. The net dipole moment is towards. Therefore, the total dipole moment is moderate.

Lewis structure and dipole moment of structure (h)

The Lewis structure of given compound is as follows:

Lewis structure of structure (h)

The direction of dipole moment is from less electronegative element to more electronegative element.

The dipole moment in the given compound is as follows:

Dipole moment in Structure (h)

Nitrogen and oxygen are more electronegative than carbon. Therefore, the direction of dipole moment of carbon-nitrogen bond is towards nitrogen and carbon-oxygen bond is towards oxygen. The total dipole moment is in upward direction. Therefore, the total dipole moment is large.