L1 - Intro to Organic Chemistry

objectives

• Know and understand the terms empirical formula, molecular formula, structural formula, displayed formula, homologous series and functional group
• Be able to apply IUPAC rules for nomenclature to simple organic compounds

What do we already know about organic chemistry?

• the chemistry of carbon compounds
• carbon has 4 electrons in its outer shell so it forms 4 covalent bonds
• these can be single bonds, double bonds or triple bonds
• carbon can form rings and long chains (which can be branched)

Key Definitions

Empirical formula shows the ratio of atoms in a compound. It is the simplest ratio in which atoms combine to form a compound

Molecular formula tells us how many of each type of atom there are in each molecule of the compound

Displayed formula shows all the bonds in the molecule as individual lines (each line represents a pair of shared electrons)

E.g. Methane

E.g. Propane

• Structural formula shows how the various atoms are bonded, without showing all the bonds - shows all atoms on each individual carbon

Methane CH₄

Propane CH₃CH₂CH₃

• Skeletal formula- all the hydrogen atoms are removed from carbon chains, leaving just a carbon skeleton with functional groups attached to it

E.g. Propane

E.g. Butane

The IUPAC System of Nomenclature

• A system for naming compounds was developed by the International Union of Pure and Applied Chemistry (IUPAC)
• Systematic names tell us about the structure of a compound rather than just the formula

e.g. methylbutane vs C₅H₁₂

• There a series of IUPAC rules for naming compounds

IUPAC Rules

2) Prefixes and suffixes describe changes to the root molecule

a) Prefixes: added before a root

e.g. Side chains – name tells us the number of carbons

methyl- CH₃-

ethyl- C₂H₅-

propyl- C₃H₇- etc.

These are alkyl groups R in a general formula

e.g. Halogen substituent

Br- bromo- Cl- chloro etc.

b) Suffixes: added after a root

used to describes most functional groups (reactive groups of atoms)

3) To tell where a side chain or functional group is on the main chain we use the number of the carbon followed by a hyphen.

Give it the lowest possible number

4) If there is more than one side chain you place them in alphabetical order

e.g. 2-bromo-3-chlorohexane

homologous series and General Formula

Homologous series

• Family of organic compounds with the same functional group but different chain length

General formula

• a formula for a family of compounds. E.g. alkanes = C_nH_2n+2 where n is the number of carbon atoms

Methane: CH₄ n=1

C_nH_2n+2

C₁H_(2x1)+2

Propane: C₃H₈ n=3

C₃H_(2x3)+2