Presentation on theme: "Advanced Higher - Unit 3 Permeating aspects of organic chemistry."— Presentation transcript:
Advanced Higher - Unit 3 Permeating aspects of organic chemistry
What is Organic Chemistry The chemistry of compounds of carbon. Except Simple oxides of carbon e.g. CO and CO 2 Carbonates e.g. K 2 CO 3, Na 2 CO 3, etc. Other simple ionic salts e.g. (NH 4 ) 2 CO 3, KCN, etc.
Why is carbon so special? Five billion compounds have been identified. More than 95% of these as compounds of carbon yet carbon only makes up 0.2% of the Earth’s crust.
The ability of carbon to form such a huge variety of compounds is due to important properties of the carbon atom itself: - carbon atoms can form four strong covalent bonds with a wide variety of other elements. - carbon atoms can form strong bonds with other carbon atoms giving rise to molecules containing chains of carbon atoms, which can be straight or branched.
-carbon atoms can form molecules containing carbon atoms (and sometimes other atoms) arranged in rings. - carbon atoms can form multiple bonds with other carbon atoms and with oxygen and nitrogen atoms.
What’s So Important About Organic Chemistry? The largest branch of Chemistry Organic Chemistry is the Chemistry of Food production Medicine Clothing manufacture (synthetic fibres and dyes) Plastics Fuels Detergents Life itself!!
Reaction types of organic compounds Addition Reaction Two or more molecules combine to produce a larger molecule and nothing else. e.g. CH 2 = CH 2 + H 2 CH 3 - CH 3 Condensation Two or more molecules combine to form a larger molecule, with the elimination of a smaller molecule (usually water). e.g. CH 3 OH + HOOCCH 3 CH 3 OOCCH 3 + H 2 O Hydrolysis A large molecule is broken into smaller molecules by reaction with water. e.g. CH 3 CH 2 Cl + H 2 O CH 3 CH 2 OH + HCl
Oxidation Increasing the proportion of oxygen:hydrogen in a compound. e.g. CH 3 CH 2 OH CH 3 COOH Reduction Increasing the proportion of hydrogen:oxygen in a compound. e.g. CH 3 COOH CH 3 CH 2 OH Substitution Replacement of an atom or group of atoms in a molecule. e.g. CH 3 -CH 3 + Br 2 CH 3 - CH 2 Br + HBr Elimination The elements of a simple molecule, like water, are removed from an organic molecule and not replaced. e.g. CH 3 CH 2 OH CH 2 = CH 2 + H 2 O
Bond Breaking All chemical reactions involve bond breaking and bond making. Bond breaking is endothermic and involves the redistribution of electrons between the two atoms. For a covalent bond there are 2 possible outcomes when it breaks (sometimes called bond fission). How a bond breaks will determine the mechanism by which a reaction proceeds. REMEMBER a covalent bond is a shared pair of electrons.
Some Important Symbols Single Headed Arrow - Shows the movement of one electron during bond forming or breaking. Double Headed Arrow - Shows the movement of two electrons during bond forming or breaking. Single Dot - Shows an unpaired electron in a free radical. Two Dots - Usually represents a lone pair of unbonded electrons (occasionally it can be used to represent a covalent bond, i.e. H:Cl)
Bond Breaking - Homolytic Fission The 2 electrons in the bond separate equally - X—Y X+ Y Homolytic fission results in two electrically neutral species (species - atoms or groups of atoms). Species with unpaired electrons are know as FREE RADICALS. Free radicals are highly reactive. Homolytic fission is more likely when the bond is non-polar.
Bond Breaking - Heterolytic Fission The 2 electrons in the bond go to one atom - Heterolytic fission results in the formation of two ions. Heterolytic fission is more likely when the bond is polar. e.g. X—Y X + +:Y - H 3 C + —Br - H 3 C + + Br -
Carbocation and Carbanions Carbocation - A positive ion where the charge is on the carbon. e.g. HHC+HHHC+H H CH 3 C + H CH 3 C + CH 3 H Carbanion - A negative ion where the charge is on the carbon. e.g. (CH 3 ) 3 C -, etc. Generally R - Both carbocations and carbanions are highly reactive and therefore usually short-lived. Generally R +
Nucleophiles and Electrophiles Nucleophile - ‘nucleus seeker’ i.e. a species that is electron rich and therefore attracted to a positive charge. e.g. Anions - OH -, carbanions, etc. Atoms with lone pairs of electrons e.g. the nitrogen atom in ammonia N - H + H + H +
Electrophile- ‘electron seeker’ i.e. a species that is electron deficient and therefore attracted to a negative charge. e.g. Cations - H +, Na +, carbocations. A partially positive atom in a polar covalent compound, e.g. the hydrogen atoms in water. O - H + H +