Chapter 11, Problem 84P

Answer the following questions about levonorgestrel (trade name Plan B). Levonorgestrel interferes with ovulation, the release of an egg from an ovary, so it prevents pregnancy if taken within a few days of unprotected sex.

  

1. Identify the functional groups.
2. How many C’s does levonorgestrel contain?
3. How many H’s are present at each C labeled with an asterisk (*)?
4. Give the shape around each atom labeled in gray.
5. Label all polar bonds.
6. Is levonorgestrel soluble in an organic solvent?
7. Is levonorgestrel soluble in water?

Interpretation Introduction

(a)

Interpretation:

The functional group in levonorgestral should be identified.

Concept Introduction:

Functional groups are the atoms or group of atoms that gives chemical properties to an organic compound and also chemical reactivity centre. Examples of functional groups are aldehyde, ketone, alcohol, alkene, alkyne etc.

Answer to Problem 84P

The functional groups present in the compound are alcohol, ketone, alkene and alkyne.

Explanation of Solution

Functional groups are the atoms or group of atoms that gives chemical properties to an organic compound and also chemical reactivity centre. Structures of different functional groups are as follows:

In the above functional group R represents an alkyl group.

In functional group ketone carbonyl carbon is bonded to two alkyl groups, in aldehyde carbonyl carbon is attached to one alkyl group and one hydrogen atom, in alcohol functional group an −OH is bonded to an alkyl group, in alkyne there is a triple bond between two carbon atoms and in alkene there is a double bond between two carbon atoms.

Levonorgestral structure is as follows:

Observe the structure of Levonorgestral. As indicated in the above figure, four types of functional groups present that is, alkene, alkyne, alcohol and ketone. The functional groups present in the compound are alcohol, ketone, alkene and alkyne.

Interpretation Introduction

(b)

Interpretation:

The number of carbon atoms in the structure of levonorgestral should be determined.

Concept Introduction:

In skeletal structure the terminals represent methyl $-{\text{CH}}_{\text{3}}$ groups, joining of two bonds in represented by methylene groups $-{\text{CH}}_2$ groups if no substituent present, if one substituent present then the group will be $-\text{CH}$.

Answer to Problem 84P

Twenty one carbon atoms present in the compound.

Explanation of Solution

The structure of Levonorgestral is as follows:

In skeletal structure the terminals represent methyl $-{\text{CH}}_{\text{3}}$ groups, joining of two bonds in represented by methylene groups $-{\text{CH}}_2$ groups if no substituent present, if one substituent present then the group will be $-\text{CH}$ . So, the complete structure of Levonorgestral is as follows:

Hence, twenty one carbon atoms present in the compound.

Interpretation Introduction

(c)

Interpretation:

The number of hydrogen atoms present in the * carbon atoms in levonorgestral should be determined.

Concept Introduction:

In skeletal structure the terminals represent methyl $-{\text{CH}}_{\text{3}}$ groups, joining of two bonds in represented by methylene groups $-{\text{CH}}_2$ groups if no substituent present, if one substituent present then the group will be $-\text{CH}$.

Answer to Problem 84P

Number of hydrogen atoms in * carbon atoms are three.

Explanation of Solution

Complete structure of levonorgestral is as follows:

From the complete structure of Levonorgestral, it is clear that number of hydrogen atoms in * carbon atoms are three.

Interpretation Introduction

(d)

Interpretation:

The shape around each indicated carbon atom in levonorgestral should be determined.

Concept Introduction:

The following table should be used while determining the shape around an atom.

Number of groups	Number of atoms	Number of lone pairs	Shape	Bond angle
2	2	0	Linear	$180°\text{C}$
3	3	0	Trigonal planar	$120°\text{C}$
4	4	0	Tetrahedral	$109.5°\text{C}$
4	3	1	Trigonal pyramidal	$109.5°\text{C}$
4	2	2	Bent	$109.5°\text{C}$

Answer to Problem 84P

Shape around carbon 1 is trigonal planar, shape around carbon 2 is tetrahedral, shape around carbon 3 is tetrahedral and shape around carbon 4 is linear.

Explanation of Solution

Given compound is as follows:

Complete structure of the compound is as follows:

• Around C1, three atoms (two carbon and one oxygen) present. So, shape around carbon 1 is trigonal planar.
• Around C2, four atoms (three carbon and one hydrogen) present. So, shape around carbon 2 is tetrahedral.
• Around C3, four atoms (two carbon and two hydrogen) present. So, shape around carbon 3 is tetrahedral.
• Around C4, two atoms ( one carbon and one hydrogen) present. So, shape around carbon 4 is linear.

Interpretation Introduction

(e)

Interpretation:

All the polar bonds in levonorgestral should be labeled.

Concept Introduction:

The unequal sharing of valence electrons in a bond is called polar bond. Polar bond result when the bond formed between two atoms in which one atom is more electronegative than the other one. One example of polar bond is $\text{H}-\text{Cl}$.

Structure of HCl is as follows:

In $\text{H}-\text{Cl}$ , Chlorine is more electronegative than hydrogen.

Answer to Problem 84P

The structure of levonorgestral with labeled all polar bonds is as follows:

Explanation of Solution

In organic compound, most of the polar bonds formed between carbon and heteroatoms like oxygen, nitrogen, sulphur etc.

In the compound, three polar bonds present. One polar bond is between carbon and oxygen where oxygen is more electronegative than carbon. Second polar bond is between carbon and oxygen where oxygen is more electronegative than carbon and third polar bond is between oxygen and hydrogen where oxygen is more electronegative than hydrogen.

The structure of levonorgestral with labeled all polar bonds is as follows:

Interpretation Introduction

(f)

Interpretation:

Whether levonorgestral is soluble in organic solvent or not should be determined.

Concept Introduction:

A compound is soluble in organic solvent if the compound contains too many hydrocarbon bonds that is if it is non-polar.

Answer to Problem 84P

The compound levonorgestral will soluble in organic solvent.

Explanation of Solution

The complete structure of levonorgestral is as follows:

The compound levonorgestral has too many carbon hydrogen bonds. So, the compound will soluble in organic solvent.

Interpretation Introduction

(g)

Interpretation:

Whether levonorgestral is soluble in water or not should be determined.

Concept Introduction:

Water is a polar solvent. To dissolve in water the compound must be polar. Polar compound is that compound in which polar bonds are present. The unequal sharing of valence electrons in a bond is called polar bond. Polar bond result when the bond formed between two atoms in which one atom is more electronegative than the other one. One example of polar bond is $\text{H}-\text{Cl}$.

Structure of HCl is as follows:

In $\text{H}-\text{Cl}$ , Chlorine is more electronegative than hydrogen.

Answer to Problem 84P

The compound levonorgestral is water soluble.

Explanation of Solution

Structure of levonorgestral is as follows:

In the compound levonorgestral, two oxygen heteroatoms present. These heteroatoms can form hydrogen bonds with water molecule and hence, the compound is soluble in water.