Organic chemistry

Organic Chemistry

• Organic means living• Hydrocarbons contain hydrogen and carbon

atoms• Organic Chemistry is the study of carbon

chemicals that are natural and artificial.• The bonding in hydrocarbons is covalent so

bonding between molecules is weak.• The structure is molecular.

Homologous seriesThis is a series of compounds which all contain the same functional group, and have similar chemical properties. 

ALKANES ALKENES ALCOHOLS

CH4 CH2 =CH2 CH3OH

CH3-CH3 CH2 =CH –CH3 CH3CH2OH

Each has a general formula:

ALKANES: CnH2n+2

The members of the series differ by the number of CH2 units.

CH3-CH3, CH3-CH2-CH3, CH3-CH2-CH2-CH3

Graduation in physical properties:  eg: boiling points.

CH4 (GAS), C8H18 (LIQUID), C30H62 (SOLID)

IUPAC

The International Union of Pure and Applied Chemistry

Why?Historical names (e.g. acetic acid,

formic acid) meant nothing to other scientists in different countries

IUPAC Rules for Alkane Nomenclature 1.   Find and name the longest continuous

carbon chain. AKA parent chain 2.   Identify and name groups attached to this chain. 3.   Number the chain consecutively, starting at the end nearest a substituent group.  4.   Designate the location of each substituent group by an appropriate number and name. 5.   Assemble the name, listing groups in alphabetical order.     The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.

Naming Alkanes

• General formula CnH2n+2

• Saturated compounds: each carbon is bonded to the maximum possible number of atoms.

“Prefix + Root + Suffix”

• Find the main chain (1 = meth, 2 = eth, 3 = prop, 4 = but, 5 = pent, 6=hex)

• Determine your suffix (Alkane = ane)• Number the main chain. Start at the end that

gives branches the lowest numbers. • Name each branch as an alkyl group (methyl,

ethyl, propyl etc.), and placing a position number in front.

• Note: always put commas between numbers, and hyphens between numbers and letters.

ALKANES SATURATED HYDROCARBONS – contain maximum amount of hydrogen - only single bonds (no multiple bonds)

GENERAL FORMULA CnH(2n+2)

NAMING ALKANESNo of C atoms

Prefix

1 Meth

2 Eth

3 Prop

4 But

5 Pent

6 Hex

7 Hept

8 Oct

All alkanes end with ‘ANE’.

All belong to the same HOMOLOGOUS series

Examples:

C

H

H H

H

C

H

H

HH

C

H

H

Methane CH4

Ethane C2H6

10

Alkyl Groups

Branches on carbon chains H

H C CH3 methyl

H

H H

H C C CH2CH3 ethyl

H H

Name these molecules

3-ethyl-3,4-dimethylhexane

STRUCTURES OF ALKANES

METHANE CH4

Bond Angle 109.5o Shape Tetrahedral

Can be illustrated as:

H

H C H

H

ETHANE. Molecular formula C2H6

Structural formula: CH3 CH3 or H H

H C C H

H H

PROPANE.

Molecular formula: C3H8Structural formula: CH3 CH2 CH3 or H H H

H C C C H

H H H

Both ethane and propane are “straight” chain moleculesBUT!! Bonds are NOT 90o molecules are NOT STRAIGHT!!!

Schematic formula

Give the names of the following alkanes(a)CH3 CH2 CH CH2 CH3

CH3

(b) CH3 CH CH2 CH CH3

CH3 CH3

(c) CH3 C(CH3)2 CH2 CH(CH3) CH2 CH3

(d) CH3CH2CH(CH3)C(CH3)3

Give the names of the following alkanes

3-methyl pentane

2,4-dimethylpentane

2,2,4-trimethyl

hexane

(a)CH3 CH2 CH CH2 CH3

CH3

(b) CH3 CH CH2 CH CH3

CH3 CH3

(c) CH3 C(CH3)2 CH2 CH(CH3) CH2 CH3

(d) CH3CH2CH(CH3)C(CH3)3 2,2,3-trimethylpentane

Cyclic Alkanes

When C atoms bond together to form a ‘ring’ – known as a ‘cyclic’ structure.

What is the molecular formula of this alkane?

How does the molecular formula compare to the general formula for alkanes?Why does it belong to the series of alkanes?

Example

Illustrate the cyclic structures of (a) C4H8

and (b) C5H10 and name the molecules.

CYCLOHEXANE

Can you think of a name for this molecule

Commas and dashes

• Use commas between numbers• Use dashes between numbers and

letters

• And one other thing; when arranging your substituent groups in alphabetical order the di, tri, tetra, etc do not count

Correct the mistakes

You have 1 minute to discuss with a partner all the mistakes in the naming of the following compounds

Name A:4-methyl-3-4-dichloro-3-bromo-pentaneName B:3-bromo-3,4-dichloro-4-methyl-pentane

H3C

CH3

CH2

CH3

C C

Cl Cl

Br

Name A:4-methyl-3-4-dichloro-3-bromo-pentaneNot alphabeticalName B:3-bromo-3,4-dichloro-4-methyl-pentane

H3C

CH3

CH2

CH3

C C

Cl Cl

Br

3-bromo-2,3-dichloro-2-methylpentane

1 2 3 4

5

Key Incorrect number Dash or comma

Worked example 1 1.   6 carbons in the longest chain hexane 2.   has 2 chloro- groups dichloroHas a methane group methyl 3.   Number the chain (see diagram)  4.   1,2-dichloro- 4-methyl 5.   1,2-dichloro-4-methylhexaneRemember: when arranging your substituent groups in alphabetical order the di, tri, tetra, etc do not count

1 2 31

23

45

6

23

Isomers

Same molecular formula

Same number and types of atoms

Different arrangement of atoms

24

Examples of Isomers

The formula C4H10 has two different structures

CH3

CH3CH2CH2CH3 CH3CHCH3

Butane 2-methylpropane

When a CH3 is is used to form a branch, it makes a new

isomer of C4H10.

25

Structural Isomers pp

Compounds that have the same molecular formula, but different molecular structures, are called structural isomers

Butane and 2-methylpropane on previous slide.

Also have different properties, such as b.p., m.p., and reactivity

26

Geometric Isomers pp

There is a lack of rotation around a carbon to carbon multiple bond–has an important structural implication–Two possible methyl arrangements:

1. trans configuration - substituted groups on opposite sides of double bond

2. cis configuration - same side

27

Geometric Isomers pp

Differ only in the geometry of their substituted groups

Like other structural isomers, have different physical and chemical properties

28

Geometric Isomers of 1,2-dichloroethene

Cl Cl H Cl C=C C=C H H Cl

H cistrans

Rigid structure so these are isomers with different properties.

29

Geometric Isomers of chloroethene? pp

H Cl H H C=C C=C H H H

Cl Rigid structure BUT both carbons

do NOT have two DIFFERENT groups attached to them.

These are just rotated in space, but are the same.

30

Nongeometric versions of 1,2-dichloroeth”ene” pp

Cl Cl H Cl C--C C--C H H Cl

H Non-rigid structure so these are

NOT isomers. (The 3rd hydrogen on each carbon is not shown)

Molecular formula: C4H10 - can have two different structures

“Straight” chain. CH3 CH2 CH2 CH3 BUTANE

Branched chain CH3 CH CH3

CH3

METHYL PROPANE

Isomers

Compounds that have the same molecular formula but different structural formula.

branch

BUTANE & ISOMERS.

Schematic formula:

TASK:

Illustrate the structures of the three different isomers of C5H12.

Names & StructuresExamples2- methylbutane

CH3

CH3 CH CH2 CH3

CH3

CH3 C CH3

CH3

2,2 – dimethyl propane

TASK: illustrate the structures of:

2-methylpentane.

2,3 – dimethylbutane.

2,2,3 -trimethylpentane

CH3CH(CH3)CH2CH2CH3

CH3CH(CH3)CH(CH3)CH3

CH3C(CH3)2CH(CH3)CH2CH3

• A by-product of CRACKING an Alkane• Used for making polymers• C=C is more reactive than C-C• The molecule is unsaturated and the double

bonds allow addition polymerisation.

Alkenes CnH2n

C C

HH

HHEthene C2H4

The shape around the double bond is planar.

The bond angle around the double bond is 120o

C C bond

PLANAR 120o

Represented as C C

Structure of Alkenes

Examples of Alkenes

………………, C2H4

H H

C C

H H

OR …………………….

PROPENE CH2 CH CH3

TASK: Use ball & stick models or sketches to construct and name 3 different structures for C4H8 each one with one double bond.

Examples of Alkenes

ETHENE, C2H4

H H

C C

H H

OR CH2 CH2

PROPENE CH2 CH CH3

TASK: Use ball & stick models or sketches to construct and name 3 different structures for C4H8 each one with one double bond.

CH3CH2CH CH2

CH3CH CHCH3

CH3C CH2

CH3

BUT-1-ENE

BUT-2-ENE

METHYL PROPENE

H H

C C

H CH3

More AlkenesIllustrate structures of the following alkenes:Pent-1-eneHex-3-ene

2-methylbut-1-ene

Cyclohexene

Name the following alkenesCH3CH CHCH2CH3

CH2 CHCH(CH3)CH2CH3CH3CH(CH3)CH CHCH2CH3(CH3)3CCH C(CH3)2

More AlkenesIllustrate structures of the following alkenes:Pent-1-eneHex-3-ene

2-methylbut-1-ene

Cyclohexene

CH2 CHCH2CH2CH3

CH3CH2CH CHCH2CH3

CH2 C(CH3)CH2CH3

Name the following alkenesCH3CH CHCH2CH3

CH2 CHCH(CH3)CH2CH3

Pent-2-ene3-methylpent-1-

eneCH3CH(CH3)CH CHCH2CH3

2-methylhex-3-ene

(CH3)3CCH C(CH3)2 2,4,4-trimethylpent-2-ene

GEOMETRIC ISOMERS There is no rotation about the double bond.

Geometric isomerism is a form of STEREOISOMERISM –

Same molecular and structural formula but atoms are arranged differently in space

GEOMETRIC ISOMERISM each C atom in the double bond has two different atoms/groups attached.

BUT–2-ENE CH3 CH CH CH3

CH3 CH3

C C

H H

CH3 H

C C

H CH3

cis but-2-enetrans but-2-ene

Alkynes

H-C≡C-H

H-C≡C-CH3

H-C≡C-CH2-CH3

CH3-C≡C-CH3

Ethyne

propyne

But–1-yne

But–2-yne

Very reactiveTriple bond unstable!Attracts electrophiles.