Homologous series

• A homologous series is a group of organic compounds that have the same functional group, the same general formula and the same chemical properties

Ethanol and propanol belong to the same homologous series

Saturated & unsaturated hydrocarbons

• Saturated?hydrocarbons are hydrocarbons which contain single bonds only resulting in the maximum number of hydrogen atoms in the molecule
• Unsaturated?hydrocarbons are hydrocarbons which contain carbon-carbon?double?or?triple?bonds

The diagram shows saturated hydrocarbons which contain single bonds only and unsaturated hydrocarbons which contain double/triple bonds as well

Homolytic & heterolytic fission

• Homolytic fission?is breaking a covalent bond in such a way that each atom takes an electron from the bond to form two radicals
• Heterolytic fission?is breaking a covalent bond in such a way that the more electronegative atom takes both the electrons from the bond to form a negative ion and leaving behind a positive ion

The diagram shows heterolytic fission in which the most electronegative atom takes both electrons in the covalent bond and homolytic fission in which each atom takes one electron from the covalent bond

Radical chain reactions

• A?free radical?is a species with one (or more than one) unpaired electrons

The diagram shows a free radical which has one unpaired electron

• A?free radical reaction?is a reaction involving free radicals and is a three-step reaction:
  • Initiation?is the first step and involves breaking a covalent bond using energy from ultraviolet (UV) light from the sun to form two free radicals
  • The?propagation?step is the second step in which the formed radical can attack reactant molecules to form even more radicals
    • These in turn can again attack other molecules to form more free radical and so on
  • In the?termination?step, two free radicals react together to form a product molecule

The diagram shows the different stages of a radical chain reactions

Nucleophiles & electrophiles

• A?nucleophile?is an electron-rich species that can?donate?a pair of electrons
  • ‘Nucleophile’ means ‘nucleus/positive charge loving’ as nucleophiles are attracted to positively charged species
  • Nucleophilic?refers to reactions that involve a nucleophile
• An?electrophile?is an electron-deficient species that can?accept?a pair of electrons
  • ‘Electrophile’ means ‘electron/negative charge loving’ as electrophiles are attracted to negatively charged species
  • Electrophilic?refers to reactions that involve an electrophile

A nucleophile ‘loves’ a positive charge and an electrophile ‘loves’ a negative charge

Types of reactions

• An?addition?reaction is an organic reaction in which two (or more) molecules combine to give a?single?product?with no other products
• A?substitution?reaction is a reaction that involves?replacing?an atom or group of atoms by another
• An?elimination?reaction is a reaction in which a small molecule (such as H₂O or HCl) is?removed?from an organic molecule
• A?hydrolysis?reaction is a reaction in which a compound is?broken?down?by?water?(it can also refer to the breakdown of a substance by dilute acids or alkali)
• A?condensation?reaction is a reaction in which two organic molecules join together and in the process?eliminate?small molecules (such as H₂O or HCl)

The different types of reactions in organic chemistry

Oxidation & reduction

• An?oxidation?reaction is a reaction in which oxygen is added, electrons are removed or the oxidation number of a substance is increased
  • In organic chemistry it often refers to the addition of oxygen or removal of hydrogen atoms to a substance
  • In equations for organic redox reactions, the symbol [O] can be used to represent one atom of oxygen from an oxidising agent
• A?reduction?reaction is a reaction in which oxygen is removed, electrons are added or the oxidation number of a substance is decreased
  • In organic chemistry it often refers to the removal of oxygen or addition of hydrogen atoms to a substance
  • In equations for organic redox reactions, the symbol [H] can be used to represent one atom of hydrogen from a reducing agent

In organic chemistry oxidation is often the gain of oxygen or loss of hydrogen atoms and reduction is the gain of hydrogen and loss of oxygen atoms