Organic Chemistry

• General Formula

  The simplest algebraic formula of a homologous series

  
• Structural Formula


  Minimal detail on the arrangement of atoms in a molecule

  
• Skeletal Formula


  Simplified organic formulae that shows the carbon skeleton, by omitting hydrogen atoms and just leaving the associated functional groups

  
• Displayed Formula


  Positioning of atoms and bonds between them

  
• Homologous Series


  A series of organic compounds with the same functional group but each successive member differs by the addition of a -CH2 group

  
• Functional Group


  Group of atoms responsible for characteristics of a compound

  
• Aliphatic


  Carbon atoms are joined to each other in unbranched (straight) or branched chains

  
• Akyl Group

  
• Alkanes


  -ane. Butane - CH3CH2CH2CH3

  
• Alkanes (branched)


  Methylpropane - CH3CH(CH3)CH3

  
• Alkenes


  -ene.

  
• Alcohol


  -ol. CH3CH2OH (ethanol)

  
• Carboxylic Acid


  -oic acid. Butanoic acid - CH3CH2CH2COOH. CnH2nO2

  
• Aldehyde


  -al. Propanal - CH3CH2CHO. Aldehydes do not need numbers.

  
• Ketone


  -one. Propanone - CH3COCH3

  
• Esters


  -oate. COOC

  
• Haloalkanes


  fluoro/chloro/bromo/iodo

  
• Homolytic Fission


  When each of the bonding atoms takes one electron from the bond. Each atom has a single unpaired electron

  
• Heterolytic Fission


  When one of the bonding atoms takes both electrons from the bond. The atom that takes both electrons becomes a negative ion and the atom that doesn't take the electrons becomes a positive ion

  
• Radical


  Species with an unpaired electron
• Curly Arrows


  Show the movement of an electron pair
• Addition Reaction


  Reactants combine to form a single product

  
• Substitution Reaction


  Where atom or group of atoms are replaced by a different atom or group of atoms
• Elimination Reaction


  Removing a small molecule from a saturated molecule to form an unsaturated molecule
• Alkanes


  Saturated hydrocarbons containing only single C-C and C-H by sigma bonds

  
• Sigma bond (σ bond)


  A covalent bond formed by the overlap of two orbitals, one from each bonding atom. The atoms can rotate freely

  
• Shape of Alkanes


  - Tetrahedral

  - Bond Angle: 109.5

  - Each carbon atom is surrounded by 4 electron pairs in 4 sigma bonds. Equal repulsion between the pairs results in the tetrahedral arrangement

  
• Effect of chain length in alkanes on their boiling point

  As the chain length increases, the molecules have a larger surface area. This means more surface contact will happen between the molecules. London forces between the molecules will be greater and more energy will be required to overcome the forces

  
• Effect of branching on boiling point

  Branched molecules have less surface contact between molecules with weaker London forces. Also, branching prevents the molecules from packing closely together, decreasing intermolecular forces further. Therefore, less energy is required to overcome these forces

  
• Why do alkanes not react with many reagents?

  - C-C and C-H sigma bonds are strong

  - C-C is non-polar

  - The electronegativity of carbon and hydrogen is very similar

  - High bond enthalpy
• Complete combustion of alkanes

  Alkanes react with a plentiful supply of oxygen producing carbon dioxide and water

  
• Incomplete combustion of alkanes

  Alkanes react with a limited supply of oxygen producing the toxic gas carbon monoxide and carbon (soot).

  - Carbon monoxide is poisonous as it binds to haemoglobin in the blood and soot can cause breathing problems
• Reaction of alkanes with chlorine and bromine (radical substitution)

  Alkanes react with halogens under UV radiation

  
• Limitations of radical substitution

  - Uncontrollable termination steps leads to a mixture of products

  - Further substitution

  - Mixture of products by substitution at different positions in a carbon chain

  
• Alkenes


  Alkenes are unsaturated hydrocarbons and contain at least one C double bond C in their structure. The double bond in alkenes has a high electron density. Alkenes are more reactive than alkanes

  
• Sigma bonds (σ bond)

  This is when 2 s orbitals overlap horizontally. There is a strong electrostatic attraction between the nuclei and shared pair of electrons.

  - This makes the sigma bond have a high bond enthalpy (and is the strongest type of covalent bond)

  
• Pi bonds (π bond)

  This is when 2 p orbitals parallel overlap/overlap sideways

  - Pi bonds are weaker than sigma bonds as the electron density is spread above and below the nuclei. The electrostatic attraction is weaker, so they have a lower bond enthalpy. This means that less energy is needed to overcome the pi bonds, making alkenes reactive

  - The position of the Pi bond's electron density above and below the plane of the sigma bond leads to restricted rotation.

  
• Shape of the double bond in alkenes

  Trigonal planar

  Bond Angle: 120

  - There are 3 regions of electron density around the carbon atoms

  - The 3 regions repel each of the carbon atoms as far as possible, so the bond angle around each carbon is 120
• Stereoisomers


  Compounds with the same structural formula but with a different arrangement of atoms in space. A molecule with have E/Z stereoisomerism:

  - C double bond

  - Different groups attached to each carbon atom in the double bond

  
• E/Z stereoisomerism


  - C double bond

  - Different groups attached to each carbon atom in the double bond