2.4 - Organic Compounds

Functional group

Atom/group which gives the compound its characteristic properties

Homologous series

A series of compounds with the same functional group and general formula

Hydrocarbon

A compound containing carbon and hydrogen onkt

Saturated compound

A compound in which all the C to C bonds are single bonds

Unsaturated compound

A compound that contains C to C multiple bonds

Molecular formula

Shows the number of atoms presents in a compound

Structural formula

Shows which atoms are bonded to which

Shortened formula

Shows the functional group and structure in sufficient detail so that the compound is unambiguous. Cannot be used if details of the bonds needed

Skeletal formula

Shows the C/H backbone of the molecule as a series of bonds with any functional groups attached. Does not show interactive chains

Displayed formula

Shows all of the atoms and bonds in the molecule. Used for mechanisms

Nomenclature rules

1. Find the longest hc chain → stem of name

2. Name C atoms, starting from side which gives smallest number

3. Identify side chains and functional groups and add to name as prefixes

4. List prefixes in alphabetical order

• Commas between numbers

• Hyphens between letters and numbers

Effect of chain length on melting + boiling temperatures

• Hydrocarbons contain only td-td VdW present between the molecules (WEAK IMFs)

• Weak IMFs act between surfaces of the molecules

• The more surface in contact, the stronger the forces so more energy needed to overcome forces

• Small hc = (g) At room temp

• Larger = liquid or solid at room temp

Effect of branching on boiling temperatures

• more branches → more spherical molecules

• Small SA available for contact

• → less SA for contact between molecules

• → weaker VdW forces between molecules → less energy needed to separate them → lower Tb

Effect of functional groups on boiling temperatures

• Increases chain length and branching

• Molecules that form H-bonds have higher Tb than those of a similar size that cannot H-bond

Effect of functional groups on solubility

• Molecules that cannot H-bond/those that can only form dp or VdW are not able to form significant attractions with the polar water molecules and therefore cannot dissolve

• Smaller alcohols/carboxylic acids/molecules which can H bond = soluble in water

• Solubility decreases as chain length increases

• As size of hc part of molecule increases, it exerts such a large hydrophobic effect on that compound is no longer soluble

Structural isomers

Compounds with the same molecular formula but with different structural formula

Types of structural isomerism

• Chain isomerism

• Position isomerism

• Functional group isomerism

Chain isomerism

• Carbon chain of molecule is arranged different differently

• One straight chained and other isomers are branched chains

Position isomers

Functional group is in a different position in the molecule

Functional group isomerism

Functional group in the compounds is different

Cyclical molecules

• General formula = CnH2n

• Each C atom in the ring is bonded to 2 H atoms

Table of homologous series

Polarity of organic molecules