Organic compounds:

Compounds from Living Things
compounds found in living organisms
Examples: sugar, fats, plant oils, urea

Characteristics of Organic Compounds

All contain carbon element
Most come with hydrogen
Others with oxygen, nitrogen, or a halogen

Some uses of Organic Compounds

Fuels
plastic
rubber
detergents
insecticides
medicines

Classifying Organic Compounds Homologeous series: a family of organic compounds with a general formula and a similar chemical properties

Functional Groups

Is the special group of atoms available in homologous series compounds which is responsible for the chemical properties of the compound
All compounds in homologous series have functional group except alkanes. Examples of functional group homologous series: alcohol

Production of Organic Compounds a. From crude oil refinery:

Crude oil is a mixture of complex hydrocarbons with varying boiling points, depending on the number of carbon atoms and how they are arranged.
Fractional distillation uses this property to separate the hydrocarbons in crude oil.

b. From naphtha:

Naphtha fraction is used for production of petrochemicals, such as medicines, plastics and synthetic fibres, aside from fuels.
When naphtha is treated, not only it becomes a better fuel, it also contain more aromatic hydrocarbons, alkene and cyclic hydrocarbons which are important for petrochemical industry.
Crude oil is mostly used as fuel, though some allocated for chemical feedstock.

Saturated vs Unsaturated Saturated hydrocarbons

hydrocarbons which the combining capacity of the carbon atoms is as fully used as possible in bonding with hydrogen atoms.
They only have single bond (–) only.

Unsaturated hydrocarbons

hydrocarbons which the combining capacity of the carbon atoms is not fully used, e.g. only 2 or 3 hydrogen are attached to a carbon atom.
usually indicated by double bond (=) or triple bond with another carbon atoms.

Alkanes Characteristics

Usually in fuels, examples: natural gas, petrol, diesel
Are homologous series
Have a formula of CnH2n+2
- example: propane has three carbon atom, thus n=3. Then the formula of propane is C3H8
Ends with suffix –ane
Next alkane formula differ by –CH2 atoms. Eg: methane: CH4, ethane: C2H6

Structure of Alkanes

Shows how all atoms in a molecule joined together by drawing lines between atoms to represent the bonds
Organic compound containing only single bond is saturated Eg: methane -
All alkanes are saturated
All alkenes are unsaturated

Physical Properties of Alkanes

Melting points and boiling points increase as the bonds become larger and heavier which increases the forces of attraction between molecules so more energy (from heat) is needed to separate them with the increase of strength of forces of attraction
insoluble in water but soluble in organic solvents such as tetrachloromethane as alkanes are organic compounds
density increases down the series; all alkenes are less than 1g/cm3
become more viscous going down the series as the longer molecules tangles together when it flows
become less flammable down the series as boiling point increases
unreactive with either metals, water, acids or bases because the C – C and C – H covalent bonds are harder to break

Reaction of Alkanes

Have same chemical properties – they don’t react with most chemicals

1) Combustion

Alkanes burn in air to ALWAYS form carbon dioxide and water.
When there is insufficient oxygen, the product is ALWAYS carbon monoxide and unburnt carbon.

Example: Butane is commonly used camping gas. State the chemical equation of combustion of butane in air. 2 C4H10 (g) + 13 O2 (g) --> 8 CO2 (g) +10 H2O (l)

High alkanes burn less completely and gives soot (unburnt carbon) and CO

2) Reaction with Chlorine/Other Halogens (Alkyl Halides)

Chlorine molecule replaces alkane hydrogen atom with chlorine atom
Substitution reaction – the reaction in which one or more atoms replace other atoms in a molecule
Light is needed to break covalent bond between chlorine molecule --> atoms

Alkenes

Characteristics- have general formula CnH2n. - all alkene names end with –ene. - the formula of one alkene differs from the next by –CH2. - have similar properties like alkane going down the series.

Structure of Alkenes

organic compound containing C = C double bond, said to be unsaturated
Reason: not all C atoms are bonded to the maximum number of 4 other atoms

The Importance of Ethene Ethanol – solvent & fuel Poly(ethene) – PE plastic variations Ethanoic acid – vinegar

Reactions of Alkenes 1) Combustion

Burns in air to form carbon dioxide and water

Example: Ethene burns in air. Write the balanced equation for the reaction C2H4 (g) + 3O2 (g) --> 2CO2 (g) + 2H2O (l)

Incomplete combustion forms soot and CO. It’s produced more than alkane

2) Addition Reaction

Is the reaction of 2 or more molecules to form a single product

a. Addition of hydrogen:

Alkenes react with hydrogen to form alkanes, called hydrogenation. Must use nickel as catalyst and heat.

b. Addition of bromine

Bromine adds to C = C double bond of alkane molecules.
Phosphoric acid (H3PO4), high temperature of 300oC and 60-70 atm pressure are needed as catalyst.
- Eg: ethene to 1,2 – dibromoethene

c. Addition of water

Alkene reacts with water, in the form of steam, to produce alcohol.
Alkene + steam is passed over phosphoric acid (H3PO4) catalyst and temperature of 300oC.
H2O molecule adds to C = C bonds to form alcohol.

3) Polymerization

The joining of several identical alkene molecules to form a big molecule

Eg: Ethene --> poly(ethene)

Testing for Unsaturated Compounds

Mix bromine solution with alkene (for liquid alkenes – shake).
Reddish-brown colour of bromine disappears.
This shows that the compound is an alkene.

Characteristics of a Homologous Series

All members of homologous series have same general formula
Formula of each member differs by –CH2 group
Physical properties changes gradually in the increase of carbon atoms
The members have similar chemical properties

The Manufacture of Margarine

Polyunsaturated food – food containing C=C bond in their molecules Eg: Vegetable oil
Hydrogen is reacted with vegetable oil with presence of nickel catalyst and heat, which adds to C=C bond, increasing the molecular mass of the compound
With increase in mass, the compound has higher boiling point. Therefore, margarine is solid at room temperature.
Since only some C=C bonds react with hydrogen, margarine is partially hydrogenated and each has different hardness, depending on the number of C=C bonds.

The Cracking of Alkanes

Alkanes can be cracked into shorter chain hydrocarbons because of the higher value it has that it can create more variety of products in petrochemical industries.
by catalytic cracking, which is, using catalyst to break alkane into simpler hydrocarbons.
crack alkane to get more valuable hydrocarbons.
The total number of carbon and hydrogen atoms from products should equal to the total number of carbon and hydrogen atoms in cracked alkane.

E.g. Octane can be cracked into simpler hydrocarbons such as the reaction below. Suggest the possible identity of product x.

C8H18 (l) --> C2H4 (g) + x + CH4 (g)

Number of C atoms in x = 8 – 2 – 1 = 5 Number of H atoms in x = 18 – 4 – 4 = 10

---> Product x is C5H10

Isomers

compounds with same molecular formula but different structural formula.
Due to different chain length, they have different physical properties (e.g. boiling point).
Isomerism can occur in both alkanes and alkenes.
For alkene, double bond position can be changed.
We therefore can’t just say that C6H14 is simply hexane because there are more variations of C6H14 and each variation has its own name.

Alcohols [size=13px]Characteristics[/size]

Are homologous series with general formula CnH2n+1OH
They have –OH functional group (hydroxyl group)
All alcohols end with suffix -ol
First three members of the series (so that you’d have idea on the next)

- Methanol, CH3OH - Ethanol, C2H5OH or CH3CH2OH - Propanol, C3H7OH or CH3CH2CH2OH

For alcohol, the –OH is not of hydroxide ion, OH-, but is covalent bond between oxygen and hydrogen, O – H

Making Ethanol 1. Fermentation of sugars with yeast 2. Reacting ethene with steam

1. Fermenting glucose

Fermentation is breakdown of sugars into smaller molecules by microorganisms.
C6H12O6 (aq) --> 2C2H5OH (aq) + 2CO2 (g)
Temperature is kept constant at 37oC to prevent destruction of yeast at higher temperatures.
Oxygen is removed by limewater and carbon dioxide is produced during fermentation.
Alcohol is separated from solution by fractional distillation.

2. Reacting Ethene with Steam

Ethene and steam are passed over phosphoric acid H3PO4 (as a catalyst) under high temperature of 300oC and pressure of 65 atm.
C2H4 (g) + H2O (g) ⇌ C2H5OH (aq)
Since this is reversible reaction, both ethene and water are produced aside from ethanol.
The ethanol is separated by fractional distillation.

Uses of Alcohol

As organic solvent
alcoholic drink; preservatives
vehicle fuel