Chemistry 30Chemistry 30

Organic Chemistry Organic Chemistry NOTESNOTES

11. Reactivity of Alkanes, Alkenes and Alkynes

Most to least – alkynes (4 Most to least – alkynes (4 bonding electrons available), bonding electrons available), alkenes (2 bonding electrons), alkenes (2 bonding electrons), and alkanes (no bonding and alkanes (no bonding electrons). electrons).

III. Important Uses of AliphaticsIII. Important Uses of Aliphatics

1. Alkanes – methane (natural gas), 1. Alkanes – methane (natural gas), butane (lighter fluid)butane (lighter fluid)

2. Alkenes – ethene: used in making 2. Alkenes – ethene: used in making plasticplastic

3. Alkynes – ethyne (acetylene): used in 3. Alkynes – ethyne (acetylene): used in welding welding

IV. Aromatics IV. Aromatics

1.1. Definition:

A special class of A special class of cyclic unsaturatedcyclic unsaturated hydrocarbons is known as aromatic hydrocarbons is known as aromatic hydrocarbons. The simplest of these hydrocarbons. The simplest of these is is benzenebenzene (C (C66HH66).).

However, evidence indicates that the However, evidence indicates that the bonds between the C’s are equal in bonds between the C’s are equal in length and strength.length and strength.

C

C

C

C

C

C

H

H

H

H

H

H

So, the actual structure is a mixture of: So, the actual structure is a mixture of:

+

Therefore, benzene is represented by:

22.. Nomenclature of Alkyl-Benzene Compounds Nomenclature of Alkyl-Benzene Compounds

USE THE FOLLOWING STEPS:USE THE FOLLOWING STEPS:

a) name the alkyl group followed by benzene

Example: methylbenzene Example: methylbenzene

(toluene)(toluene)

CH3

b) if the alkyl group is attached by a middle carbon, consider, the benzene as an alkyl group called phenylphenyl

Example: 2-phenylpropane Example: 2-phenylpropane CH CH3CH3

c) if 2 H’s are replaced in benzene, the

replaced groups can be arranged in 3 ways

Example:

1. Ortho 2. Meta 3. Para

(adjacent C’s) (1C between) (2C’s between) CH3

CH2 CH3

CH3

CH2 CH3

CH3

CH2 CH3 O-ethylmethylbenzene

or

1-ethyl-2-methylbenzene

M-ethylmethylbenzene

or

1-ethyl-3-methylbenzene

P-ethylmethylbenzene

or

1-ethyl-4-methylbenzene

d) if 3 H’s are replaced, number so that the lowest possible number combination is achieved. Then name alphabetically.

Example:

i. 1-ethyl-3-methyl-5-propylbenzene

NOT 3-ethyl-5-methyl-1-propylbenzene

CH3

CH2 CH3CH2CH2CH3

ii. 4-ethyl-1,2-dimethylbenzene

NOT 1-ethyl-3,4-dimethylbenzene

CH3

CH3CH2

CH3

3. Properties of Benzene3. Properties of Benzene

Liquid at room temperature, boils at 80.1 C

Non-polar so insoluble in water Behaves like an alkane: addition

reaction do NOT occur Substitution reactions DO occur

Example:

+ Cl Cl

Cl

+ ClH

This is because there is no definite double bond for the addition reaction to occur on.

3. Properties of Benzene3. Properties of Benzene

Also found in number of explosives

Example: trinitrotoluene (TNT)

CH3

N+

O-

O

N+

O-

O

N+

O-

O

A little more about Benzene

benzin, benzol, benzene

Discovery

1825- Michael Faraday- first to isolate & identify

1836- Auguste Laurent (French) named it “phène”

1855- August Wilhelm Hofmann used the word “aromatic” to describe the family.

1865- Friedrich August Kekulé (German) had a dream

Uses

After-shave lotion Solvent for degreasing metals Decaffeinate coffee paint strippers rubber cements spot removers gasoline additive

Health Issues...

“it’s generally considered that the only absolutly safe concentration for benzene is zero” (The American Petroleum Institute, 1948)

Know carcinogen- causes leukemia Was first known to cause cancer in the

1920s but it wasn’t until 1979 until it was “conclusive”

Still used today...

Max 1% as a gasoline additive to make styrene and Nylon rubbers lubricants dyes detergents drugs explosives & napalm pesticides

Learning Activities Groups of 2: Make six flash cards.

Draw a diagram on one side, name it on the other! Don’t forget IUPAC!

Homework Page 11 Go back through the workbook and

find any aromatic question that we skipped!