Chapter 12 - Organic Chemistey 2 Functional Groups

Question 0

What ability does the presence of functional groups in a molecule have?

Answer 0

The predictive ability of the types of reactions the molecule will undergo.

Question 1

What is a functional group?

Answer 1

It is an atom or a group of atoms that determines the chemical and, in part, physical properties of an organic compound.

Question 2

List some if the functional groups of simple molecules.

Answer 2

• alcohol
• aldehyde
• carboxylix acid
• ketone
• amine
• ester

Question 3

What are some of the chemistry of functional groups related to?

Answer 3

The changing oxidation number of the carbon atom that is a part of the group.

Question 4

What is the functional group present on an alcohol?

Answer 4

It is the -OH group attached to a tetrahedral carbon atom.

Question 5

What are the physical properties of simple alcohols? (Up to 8 carbon atoms)

Answer 5

• Colorless liquids at room temperature.

• Boiling point of an alcohol is higher than that of the parent Alkane.
-This is due to the presence of hydrogen bonds as well as dispersion forces between the alcohol molecules, compared to only dispersion forces holding the Alkane molecules together.

Question 6

List the boiling points of some alcohol.

Answer 6

1. Methanol 65
2. Ethanol 78
3. Propan-1-ol 97
4. Butan-1-ol 118

Question 7

When do hydrogen bonding occur?

Answer 7

It occurs between molecules where a hydrogen atom is bonded to one of the 3 highly electronegative atoms - nitrogen, oxygen or fluorine.

Question 8

Can hydrogen bonding occur with Alkanes?

Answer 8

• No because there are only carbon and hydrogen atoms.

* Only dispersion forces can exist between Alkane molecules.

Question 9

Why do alcohols have a much higher melting and boiling points than parent Alkanes?

Answer 9

This is because hydrogen bonds are stronger than dispersion forces, and because there will be dispersion forces present in the Alkanes as well.

Question 10

When does the strength of dispersion forces increase?

Answer 10

• They increases with the increasing number of electrons in the molecule.
• The alcohol molecule with larger molecular masses have more atoms present in the molecule and so have more electrons.

Question 11

When does the solubility of alcohol in water decreases?

Answer 11

• When the molecular mass increases. Alcohols with smaller molecular masses are soluble in water.
• After butanol, the alcohols are essentially insoluble in water.

Question 12

Why can’t longer chains of alcohol be broken down?

Answer 12

This is because the small number of hydrogen bonds that form between the alcohol functional group on he alcohol and surrounding water molecule is not sufficient to make up for the bonds that have to be broken between water molecules.

Question 13

List the type d Alcohols.

Answer 13

1. Primary Alcohol - one carbon atom and two hydrogen atoms are attached to the carbon atom to which the -OH group is bonded.
2. Secondary Alcohol - two carbon atoms and one hydrogen atom are attached to the carbon atom to which the -OH group is bonded.
3. Tertiary Alcohol - three carbon atoms and no hydrogen atoms are attached to the carbon atom to which the -OH group is bonded.

Question 14

Which alcohols are the most reactive?

Answer 14

1. Primary
2. Secondary
3. Tertiary

Question 15

What happens when the hydrocarbon chain of the alcohol increases in length?

Answer 15

The reactivity of the alcohol decreases as the likelihood of a successful collision between the alcohol functional group and the metal is reduced.

Question 16

What are the two most common reactions of alcohols?

Answer 16

Oxidation and Reduction which forms another group of compounds called esters.

Question 17

How can aldehydes be formed?

Answer 17

By the oxidation of primary alcohols.

Question 18

What does the oxidation of primary alcohols to aldehydes involve?

Answer 18

It involves the reactions of the alcohol with an oxidizing agent such as an acidified solution of potassium dichromate or an acidified solution of potassium permanganate with the aldehyde being carefully removed (often by distillation) from the reaction mixture as it is formed.

Question 19

How is a carboxylic acid form?

Answer 19

• When an aldehyde is not removed after it is formed, it will react further to produce a compound containing another functional group which is the carboxylic acid group.
• Carboxylic acids are prepared by the oxidation of primary alcohols or aldehydes, using acidified dichromate or permanganate solutions.

Question 20

How to ensure that the oxidation of a primary alcohol forms a Carboxylic Acid and not an Aldehyde ?

Answer 20

The reaction mixture is normally heated for some time, for eg. 30 minutes.

•The oxidation of methanol, and methanol, often leads to the formation of carbon dioxide, rather than methanoic acid, when these conditions are used.

Question 21

Why do carboxylic acids only partially ionize?

Answer 21

• Because they are weak acids.

* Generally, the acid strength decreases with increasing length of the carbon chain.

Question 22

Why do carboxylic acids tend to have a higher melting and boiling point?

Answer 22

• Hydrogen bonds formed between carboxylic acid molecules.
• The formation of dimers (combinations of two molecules joined together)
• Also, in general, each carboxylic acid can form hydrogen bonds ‘through’ two of its atoms.

Question 23

Why is it not possible for secondary alcohols to be oxidized to form an aldehyde or carboxylic acid?

Answer 23

Because in secondary alcohols, the -OH functional group is not on a terminal or end carbon atom.

Question 24

What does the oxidation of secondary alcohols produce?

Answer 24

Under the same conditions as those used for primary alcohols it produces a new functional group - the ketone group.

Question 25

How is a ketone formed?

Answer 25

Ketones are formed from the oxidation of secondary alcohols, using acidified dichromate or permanganate solutions.

Question 26

Will tertiary alcohols undergo any oxidation?

Answer 26

No.

Question 27

Summaries the oxidation of alcohols.

Answer 27

Oxidant: Acidified dichromate / Acidified permanganate solution * Primary -> mild conditions produce the aldehyde (RCHO), which can be distilled from the reaction mixture. After heating for a period of time, the carboxylic acid (RCOOH) is produced. * Secondary -> formation of the ketone (RCOR') * Tertiary -> No reaction.

Question 28

How do Early Breathalyzers work?

Answer 28

* It consisted of a tube packed with orange potassium dichromate granules and a plastic bag at the end. * As the suspect breathed through the tube to fill up the bag, if there was ethanol in the breath, the orange crystals would change to a green colour of chromium (III) ions. * If the amount of green colour formed exceeded a particular distance along the tube then the person was considered to have a sufficiently high reading to warrant a more accurate blood alcohol test being performed.

Question 29

Can alcohols undergo oxidation when they are burnt in air or oxygen?

Answer 29

Yes, the products of the reaction of an alcohol with excess air are carbon dioxide and water.

Question 30

How are Esters formed?

Answer 30

Esters are formed in the reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst such as concentrated sulfuric acid.

Question 31

What happens during the formation of an ester?

Answer 31

* The mixture is normally heated for some time, during which a condensation reactions takes place. * Such reactions involve the elimination of a water molecule as the acid combines with the alcohol. * In this reaction, the hydrogen from the alcohol group combines with the OH from the carboxylic acid to form water.

Question 32

What is hydrolysis?

Answer 32

The reverse of the esterification.

Question 33

How does Hydrolysis occur? (Esters converted back to the original carboxylic acid and alcohol)

Answer 33

* When the esters are reacted with an acid, usually with warming. * Warming the ester with a solution of sodium hydroxide (or similar base) can also result in the hydrolysis of the ester. * In this case the products of the reaction are the alcohol and the salt of the carboxylic acid.

Question 34

How are amines related to ammonia ?

Answer 34

* structure * polar molecules * capable of hydrogen bonding to one another and other polar molecules containing oxygen, nitrogen and fluorine. * pungent smell; particularly those of lower molecular mass that are more volatile. * weak base.

Question 35

Why are the hydrogen bonding interaction between amines weaker than that between alcohols?

Answer 35

Because the electronegativity difference between nitrogen and hydrogen is less than that between oxygen and hydrogen.

Question 36

Why do amines have a lower boiling point than alcohols?

Answer 36

This is due to the Weaker hydrogen bonding.

Question 37

Why do amines with lower molecular masses usually more soluble in water?

Answer 37

This is due to their ability to hydrogen bond to the abundant water molecules. Increase in molecular mass = decrease in solubility.

Question 38

Why are many prescribed drugs amine?

Answer 38

* Because they are often insoluble in water, getting them into body fluids such as blood plasma is difficult. * However, by making use of the basic properties of the amine, the molecule can be converted to a soluble salt by reaction of the amine with an acid such as Hydrochloric acid.

Question 39

What died the name "amino acid" suggests?

Answer 39

That these compounds contain an amine and a carboxylic acid functional group.

Question 40

What does the alpha sign stand for?

Answer 40

It is used to show that the two functional groups are attached to the same, terminal carbon atom.

Question 41

What does amphoteric mean?

Answer 41

* When a chemical can behave as either an acid or a base. | * This occurs in alpha amino acids as they have both and acidic and a basic functional group.

Question 42

What is a Zwitterion?

Answer 42

* When compounds have a positive charge on one atom and a negative charge on another. * There are no un-ionized alpha amino acids. * This characteristic of all amino acids means that not only are they amphoteric but they are also buffers.