A-LEVEL AQA ChEMISTRY NOTES
Introduction to organic chemistry
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- Hydrocarbons can be:
- Aliphatic- carbon atoms form straight or branched chains
- Alicyclic- carbon atoms form a ring
- Aromatic - carbon atoms form a ring and have a delocalised electron system
- Homologous series are compounds with the same functional group and similar chemical and physical properties. They differ by the number of repeating units they contain
- A functional group is the group of atoms responsible for the characteristic reactions of a compound.
- To name a compound:
- The stem is the main part of the name derived from the longest carbon chain.
- The suffix after the stem, comes from the most significant functional group
- The prefix before the stem comes from functional groups attached to the main carbon chain
- Numbers and hyphens indicating the position of functional groups on the carbon chain
- Functional groups are prioritised alphabetically
- General formula- the simplest algebraic formula for a homologous series
- Structural formula gives the minimum detail on the arrangement of atoms in a molecule, without drawing any bonds
- Molecular formula shows the number and types of atoms of each element in a compound. However, it does not give any information on how the molecule is bonded together.
- Skeletal formula is a simplified formula used to represent organic molecules. Lines represent bonds between atoms, junctions are carbon atoms. Other labels are omitted.
- Displayed formula shows the relative positioning of atoms and the bonds between them. All atoms and bonds are shown
- Empirical formula the simplest whole-number ratio of each element present in a compound.
- Bond fission can be homolytic or heterolytic
When the bond breaks, each electron in the bond goes to a different atom.
This results in the formation of highly reactive free radicals, each with an unpaired electron, represented by a dot.
When the bond breaks, both the electrons in the bond go to the same atom
This results in the formation of a positively charged cation and a negatively charged anion.
- Bonds are formed on the collision of:
- Two free radials with unpaired electrons
- Oppositely charged ions
- Isomers are compounds with the same molecular formula but a different arrangement of atoms
- Structural isomers are compounds with the same molecular formula but a different structural formula
- Chain isomers- These are molecules with the same molecular formula but a different arrangement of the carbon chain. Chains can be straight or branched
- Position isomers- These are molecules with the same functional group attached to a different position on the carbon chain
- Functional group isomers- These are molecules with the same molecular formula but different functional groups
- Stereoisomers are organic compounds with the same molecular and structural formulae but a different arrangement of atoms in space
- E/Z isomerism is a type of stereoisomerism that can arise in alkenes due to the restricted rotation around the C=C bond.
- If a carbon atom has two of the same substituent attached, it will not show E/Z isomerism
- Substituents can be assigned priorities based on atomic mass using Cahn-Ingold-Prelog rules to name E/Z isomers. The greater the atomic mass, the higher the priority
- When the highest priority groups are on different sides of the double bond, the isomer is an E-isomer.
- When the highest priority groups are on the same side of the double bond, the isomer is a Z-isomer