Characteristics of Organic Compounds
- Compounds from Living Things
- compounds found in living organisms
- Examples: sugar, fats, plant oils, urea
- All contain carbon element
- Most come with hydrogen
- Others with oxygen, nitrogen, or a halogen
Some uses of Organic Compounds
Classifying Organic Compounds
Homologeous series: a family of organic compounds with a general formula and a similar chemical properties
Production of Organic Compounds
- 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
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:
Saturated vs Unsaturated
- 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.
- 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.
- 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.
Structure of Alkanes
- 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
Physical Properties 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
Reaction 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
- Have same chemical properties – they don’t react with most chemicals
- 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
- 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
The Importance of Ethene
- 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
Ethanol – solvent & fuel
Poly(ethene) – PE plastic variations
Ethanoic acid – vinegar
Reactions of Alkenes
- 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.
- The joining of several identical alkene molecules to form a big molecule
Eg: Ethene --> poly(ethene)
Testing for Unsaturated Compounds
Characteristics of a Homologous Series
- Mix bromine solution with alkene (for liquid alkenes – shake).
- Reddish-brown colour of bromine disappears.
- This shows that the compound is an alkene.
The Manufacture of Margarine
- 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 Cracking of Alkanes
- 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.
- 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
- 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.
- 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
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