Chapter 21, Problem 40E

(a)

Interpretation Introduction

Interpretation: The solubility of minoxidil in acidic and basic aqueous solution should be determined.

  

Concept Introduction: The Lewis structure of an organic compound represents the bonding of atoms with lone pairs (if any). It indicates the bonds with atoms and also arrangement of atoms in molecule.

Hybridization of any atom indicates the molecular geometry of molecule. The formula to check the hybridization can be written as:

Hybridization = Number of sigma bonds + Number of lone pair

Answer to Problem 40E

Minoxidil must be soluble in acidic aqueous solution.

Explanation of Solution

Minoxidil contains two −NH₂ groups. The amine groups are basic in nature as N atom of this functional group contains one lone pair. Thus it must be soluble in acidic aqueous solution.

As in acidic solution, it will form salt and therefore will be soluble.

(b)

Interpretation Introduction

Interpretation: The hybridization of five nitrogen atoms in minoxidil should be determined.

  

Concept Introduction: The Lewis structure of an organic compound represents the bonding of atoms with lone pairs (if any). It indicates the bonds with atoms and also arrangement of atoms in molecule.

Hybridization of any atom indicates the molecular geometry of molecule. The formula to check the hybridization can be written as:

Hybridization = Number of sigma bonds + Number of lone pair

Answer to Problem 40E

  $\begin{array}{l}{\text{-NH}}_{\text{2}}{\text{; hybridization= 3 sigma bonds+1 lone pair = 4 = sp}}^{\text{3}}\\ {\text{=N-; hybridization= 2 sigma bonds+1 lone pair = 3 = sp}}^{\text{2}}\end{array}$

Explanation of Solution

  

Minoxidil contains two −NH₂ groups. There are three N atoms in the ring. Thus the hybridization of N atoms are:

  $\begin{array}{l}{\text{-NH}}_{\text{2}}{\text{; hybridization= 3 sigma bonds+1 lone pair = 4 = sp}}^{\text{3}}\\ {\text{=N-; hybridization= 2 sigma bonds+1 lone pair = 3 = sp}}^{\text{2}}\end{array}$

(c)

Interpretation Introduction

Interpretation: The hybridization of each carbon atoms in minoxidil should be determined.

  

Concept Introduction: The Lewis structure of an organic compound represents the bonding of atoms with lone pairs (if any). It indicates the bonds with atoms and also arrangement of atoms in molecule.

Hybridization of any atom indicates the molecular geometry of molecule. The formula to check the hybridization can be written as:

Hybridization = Number of sigma bonds + Number of lone pair

Answer to Problem 40E

  $\begin{array}{l}{\text{>CH}}_{\text{2}}{\text{; hybridization= 4 sigma bonds+0 lone pair = 4 = sp}}^{\text{3}}\\ {\text{=CH-; hybridization= 3 sigma bonds+0 lone pair = 3 = sp}}^{\text{2}}\end{array}$

Explanation of Solution

  

Minoxidil contains two types of C atoms. The double bonded carbon atoms are part of one ring whereas another ring contains only single bonded C atom.

  $\begin{array}{l}{\text{>CH}}_{\text{2}}{\text{; hybridization= 4 sigma bonds+0 lone pair = 4 = sp}}^{\text{3}}\\ {\text{=CH-; hybridization= 3 sigma bonds+0 lone pair = 3 = sp}}^{\text{2}}\end{array}$

(d)

Interpretation Introduction

Interpretation: The bond angles marked as a, b, c, d, e and f in the given molecule of minoxidil should be determined.

  

Concept Introduction: The Lewis structure of an organic compound represents the bonding of atoms with lone pairs (if any). It indicates the bonds with atoms and also arrangement of atoms in molecule.

Hybridization of any atom indicates the molecular geometry of molecule. The formula to check the hybridization can be written as:

Hybridization = Number of sigma bonds + Number of lone pair

Answer to Problem 40E

1. 109°
2. 109°
3. 120°
4. 120°
5. 109°
6. 120°

Explanation of Solution

The hybridization of bonded atoms determines the bond angle.

  $\begin{array}{l}{\text{-NH}}_{\text{2}}{\text{; hybridization= 3 sigma bonds+1 lone pair = 4 = sp}}^{\text{3}}\\ {\text{=N-; hybridization= 2 sigma bonds+1 lone pair = 3 = sp}}^{\text{2}}\end{array}$

  $\begin{array}{l}{\text{>CH}}_{\text{2}}{\text{; hybridization= 4 sigma bonds+0 lone pair = 4 = sp}}^{\text{3}}\\ {\text{=CH-; hybridization= 3 sigma bonds+0 lone pair = 3 = sp}}^{\text{2}}\end{array}$

A sp³ hybrid C atom has 109° bond angle with tetrahedral geometry whereas a sp² hybrid C atom has 120 ° bond angle with trigonal planer geometry. Similarly the single bonded N atom has 109° bond angle whereas a double bonded N atom has 120° bond angle. Thus, the marked bond angles must be:

1. 109°
2. 109°
3. 120°
4. 120°
5. 109°
6. 120°

(e)

Interpretation Introduction

Interpretation: Interpret the number of sigma bonds in the given molecule including hydrogen atoms.

  

Concept Introduction: The Lewis structure of an organic compound represents the bonding of atoms with lone pairs (if any). It indicates the bonds with atoms and also arrangement of atoms in molecule.

Hybridization of any atom indicates the molecular geometry of molecule. The formula to check the hybridization can be written as:

Hybridization = Number of sigma bonds + Number of lone pair

Answer to Problem 40E

There are total 30 sigma bonds in the molecule.

Explanation of Solution

A single covalent bond is formed by one sigma bond whereas one double bond is composed of one sigma bond and one pi bond.

Each C atom must be bonded with four other atoms. Therefore in the bond line formula, each C atom must be bonded with other C or N atom and the tetravalency will be completed with H atoms.

Thus there are total 30 sigma bonds in the given molecule.

(f)

Interpretation Introduction

Interpretation: Interpret the number of p-bonds in the given molecule.

  

Concept Introduction: The Lewis structure of an organic compound represents the bonding of atoms with lone pairs (if any). It indicates the bonds with atoms and also arrangement of atoms in molecule.

Hybridization of any atom indicates the molecular geometry of molecule. The formula to check the hybridization can be written as:

Hybridization = Number of sigma bonds + Number of lone pair

Answer to Problem 40E

There are total 3 p-bonds in the molecule.

Explanation of Solution

A single covalent bond is formed by one sigma bond whereas one double bond is composed of one sigma bond and one pi bond.

Each C atom must be bonded with four other atoms. Therefore, in the bond line formula, each C atom must be bonded with other C or N atom and the tetravalency will be completed with H atoms.

Thus, there are total 3 p-bonds in the given molecule.