Theme 4:  Organic Chemistry and Analysis

TOPIC 4.1 FOUNDATIONS OF ORGANIC CHEMISTRY

Formula in Organic Chemistry

General Formula

Applied to chemicals in the same family

  • Alkanes, Cn H2n+2

  • Alkenes, Cn H2n

  • Alcohols, Cn H2n+1

Displayed Formula 

All the atoms and all the bonds

Structural Formula

Arrangement of atoms in a molecule without showing all the bonds. 

Infixes

Meaning

-an-

all C-C

-ene-

one C=C

-yn-

one C≡C

-dien-

two C=C 

-trien-

three C=C

Condensed Formula

Each Carbon atom listed separately along with the other atoms it is attached to.

E.g. C6H14 can be expressed as CH3C(C2H6)CH(C2H5)CH2CH2CH2

  

Skeletal Formula

Only bond lines and functional groups are shown. 

Homologous series:  group of compounds that have the same functional group and general formula but different lengths of carbon chains.

Functional group: the reactive group attached to the physical and chemical properties of the compound in a specific homologous series.

Homologous series

Prefix or suffix

Example

Alkanes

-ane

Butane

Alkanes (branched) 

alkyl-

Methyl-propane

Cycloalkanes

cyclo- and -ane

Cyclopentane

Alkenes

-ene

Propene

Haloalkenes

fluoro-/chloro-/bromo-/iodo- and -alkane

Bromoethane

Alcohols

-ol

Ethanol

Aldehydes

-al

Propanal

Ketones

-one

Propanone

Carboxylic acids

-oic acid

Butanoic acid

Esters

alkyl- and -anoate

Methyl ethanoate

Amines

-amine

Propan-1-amine

Basic rules for naming organic compounds

  1. Find longest carbon chain

  2. Decide suffix based on functional group

  3. Decide prefix based on functional group and substituents

  4. Functional group on lowest carbon number, number before suffix. Butan-1-ol.

  5. Side chains written as prefixes in alphabetical order.

  6. Identical functional groups get di-, tri-, tetra-, etc.

 

Bond fission

  • ⟶Breaking of a covalent bond.

Heterolytic fission (heterolysis)

When a covalent bond is broken and the shared pair of electrons is taken by one species with the fewer electrons, to form a cation and an anion.

Homolytic fission

When a covalent bond is broken and the pair of electrons in the bond are shared equally to form two uncharged species, called radicals.

 

Free radicals

  • Atom with an unpaired valence electron

  • Very reactive intermediates

  • Combine with others to form new covalent bonds

Initiation

  • ⟶Radicals are produced

  • ⟶Visible normally or ultraviolet light

  • ⟶Photochemical reaction; reaction started by the absorption of light.

Propagation

  • ⟶When one radical reacts with a non-radical molecule.

  • ⟶New radicals are created and react with other non-radicals (chain reaction)  

Termination

  • ⟶When two radicals react they form a non-radical molecule

  • ⟶Ending chain reaction