Hydrocarbons / Organic Chemistry

Organic Chemistry

• Organic chemistry is the study of the structure, properties, composition, reactions, and preparation of the chemical compounds that contain carbon.

Hydrocarbons• Hydrocarbons are molecules which

contain hydrogen and carbon

• There are many different compounds that can form with carbon and hydrogen

• There are 3 main hydrocarbon families

1. Alkane

2. Alkene

3. Alkyne

Where do you find hydrocarbons?• Carbon compounds make up 90% of all

chemical compounds and many form the basis of living systems

• The majority of hydrocarbons found naturally occur in crude oil

• Crude oil forms from decomposed organic matter which has lots of carbon and hydrogen!.

• Proteins, carbohydrates and fats

all contain carbon, hydrogen and

oxygen

What are the differences and similarities of the compounds below

1. Alkanes• Are hydrocarbons that contain only carbon

and hydrogen

• They only have single bonds

• CnH2n + 2

• A series of compounds with similar properties in which each member differs from the previous one by –CH2 is known as a homologous series

• Structural formulas show the number and location of bonds but not lone pairs

Straight and branched chain• A straight-chain is where the carbon atoms in an

alkane, alkene and alkyne form a chain that runs from one end of the molecule to the other.

• A branched chain is were an alkane, alkene and alkyne has alkyl groups bonded to its central carbon chain.

• An alkyl is a group of atoms consisting of carbon and hydrogen atoms, arranged in a chain.

Naming carbon compoundsNo. of carbon Atoms

Prefix

1 Meth-

2 Eth-

3 Prop-

4 But-

5 Pent-

6 Hex-

7 Hept-

8 Oct-

9 Non-

What are the differences and similarities of the compounds below

2. Alkenes• Contains at least one carbon to carbon

double bond

• The alkenes are a homologous series

• CnH2n n = integer

Naming Alkenes• Carbon atoms are

labelled from left to right

• Identify where the double bond starts

• And put that number between the prefix and suffix of the alkene

But-1-ene

But-2-ene

Naming alkenes with 2 double bonds

• If there are two double bonds the suffix (ending) is -diene

• 3 double bonds -triene

• buta-1, 2-diene

3. Alkynes

• Are hydrocarbons that contain only carbon and hydrogen

• They have at least one triple bond

• The alkynes are a homologous series

Naming carbon compounds

Suffix

If all of the carbon to carbon bonds are single

-ane

If there is at least one carbon-carbon bond is a double bond

-ene

If there is at least one carbon-carbon bond is a triple bond

-yne

Structural isomers• Structural isomers are molecules with the

same molecular formula but different arrangement of their atoms (different structural formulas)

Structural Isomers

Structural isomers

Semi-structural formulas

• Semi- structural formula is a structural formula without giving the arrangement atoms in space

Make and then draw as many isomers of hexane as possible

Naming isomers1. Name and number longest carbon chain (circle it)

2. Identify branches (there are no branches at ends!)

3. Name each branch (alkyl group) put them in alphabetical order

• methyl CH3 ethyl C2H5 propyl C3H7 butyl C4H9

pentyl C5H11

4. If there is more than 1 alkyl group use:

di = 2, tri = 3, tetra = 4 as a prefix e.g. diethyl, trimethyl

5. Write the number of the carbon atom each alkyl group is attached to. Put commas between numbers if there is more than one alkyl group (2,3-dimethyl)

6. Put hyphens between numbers and words (2,2 – dimethylbutane)

Name the following

• n2-methyl propane

propane

Name the following carbon compounds

5-ethyl-5,6,6-trimethyl decane

4,5-diethyl-5,6-dimethyl-4-propyloctane

Are these named correctly?

Rewrite the names that are incorrect

Name all the isomers of hexane you drew

Saturated compounds

• A saturated compound has no double or triple bonds.

• In saturated linear hydrocarbons, every carbon atom is attached to two hydrogen atoms, except those at the ends of the chain, which have three hydrogen atoms.

• In the case of saturated methane, four hydrogen atoms are attached to the single, central carbon atom.

• Of simple hydrocarbons, alkanes are saturated, and alkenes are unsaturated.

Unsaturated carbon compounds

• Alkenes and alkynes are unsaturated carbon compounds because they contain less hydrogen than the maximum amount possible

Which compound/s are saturated?

• v

Physical Properties of Alkanes and Alkenes

• As the number of carbon atoms increases in a homologous series there is a change in the physical properties

• At room temperature, the lighter alkanes and alkenes are gases; the midweight alkanes are liquids; and the heavier alkanes are solids, or tars.

• Why?

• London forces increase as molecules get heavier

Boiling Point

• The boiling points of the alkanes and alkenes gradually increase with the molecular weight of the compounds.

• Alkanes and alkenes have similar boiling points

• Alkenes have a slightly lower

Hydrocarbons Boiling point (C)

Methane -161.5

Ethane -88.6

Propane -42.1

Butane -0.5

Pentane 36.1

Volatility• Volatile liquids are those

that evaporate (go from liquid to solid) easily.

• Smaller molecules are more volatile

• Why?• Because there are weak

London forces so it is easier for them to go from a liquid to a gas

Viscosity• Viscosity is the measure of the thickness of a

fluid• Honey is more viscose (it is harder to pour)

than water• The larger the molecule the more viscous it is• The larger the molecule the stronger the

London forces which means they are more likely to stick together because they are long they get tangled up like spaghetti

Hydrocarbon Solubility

• The rule to use when determining hydrocarbon solubility is: Like dissolves like.

• This means that polar compounds (water, and alcohols) dissolve other polar compounds.

• Nonpolar compounds dissolve other nonpolar compounds but tend not to dissolve polar compounds.

Chemical Properties of Alkanes• Alkanes burn in oxygen this is called a

combustion reaction

• The reactants are hydrocarbon and oxygen

• The products are water and carbon dioxide

Combustion reaction• Combustion reactions are whats causing

global warming!

• Petrol, made up of hydrocarbons combusts in cars engines

Chemical Properties of Alkenes

• Alkenes have different chemical properties to alkanes due to the double bonds in alkenes

• Alkenes react much more readily than alkanes

Reaction with bromine solution• Ethene reacts with bromine and bromine is

added to the ethene molecule. Ethene loses its double bond

• This is called an addition reaction because bromine is added to ethene

Reaction with bromine solution

• This is used to test for unsaturation

• If the solution is unsaturated the red brown colour of bromine disappears

• The red brown colour disappears becasue the bromine becomes part of the ethene molecule

• Permanganate solution is also used to test for unsaturation

Test for unsaturation• Bromine does not react with an alkane

because the alkane contains only single C-C bonds which cannot add the bromine. Alkanes merely dilute the red-brown bromine color to an orange or yellow color

• Due to their C=C double bonds which can be broken, alkenes react readily with bromine to produce saturated dibromoalkanes.

Reaction of alkane with halogens

• The reaction of alkanes follows the general rule

• Br2 + alkane alkane–Br + HBr

Ethene and Hydrogen reaction• Ethene reacts with hydrogen gas to form

ethane

• This is an example of an addition reaction

Reaction with steam

• Ethene reacted with steam (water) forms ethanol

Functional groups aside from alkyl groups

• OH, hydroxy alkanolFunctional group Name of functional

groupHomologous series

• http://www.sciencegeek.net/APchemistry/APtaters/alkanes.htm