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  +