Basic concepts of core organic chemistry

• General formula --> the simplest algebraic formula of a member of a homogenous series

  CnH2n+2 --> Alkanes

  CnH2n --> Alkenes
• Homologous series --> a series of organic compounds having the same functional group but with each successive member different by CH2. E.g: Alcohols, alkenes, alkanes, esters
• Functional group --> a group of atoms responsible for the characteristic reactions of a compound
• Nomenclature:

  Organic compounds are named according to their:

  • Stem --> the longest continuous chain of carbons
  • Functional group --> given as prefixes or suffixes
• Aliphatic --> carbon chain
• Alicyclic --> carbons in a ring
• Aromatic --> have a benzene ring
• Nomenclature - branching:

  If a compound has branches coming off the stem, they are referred to as alkyl groups.

  • They have the suffix -yl
  • Branches are numbered to indicate where they are found o the stem, bust must be from the shortest route
  • count the longest continuous chain
  • Determine the shortest direction to the branch
  • Count the branch chain length
• Naming alkenes:

  • The longest carbon chain
  • number from side where the carbon double bond is closest to
  • Only write small numbers in the name
• Nomenclature - functional group:

  A functional group is a species that gives a compound its distinctive chemical and/or physical properties.
• Alkane, alkenes, alkynes are homologous series within aliphatic hydrocarbons
• Stem, prefix and suffix:

  • The stem of the name indicates the number of carbon atoms in the longest continuous chain in the molecule
  • A prefix can be added before the stem, often to indicate the presence of side chains or a functional group
  • A suffix is added after the stem o indicate functional groups
• Naming aliphatic alkanes:

  • All alkanes have the suffix -ane
  • Identify the longest continues chain of carbon atoms (the ‘parent’ chain) and name it.
  • Identify any side chains attached to the parent chain. these side chains are known as alkyl group. The name of the alkyl group is added as a prefix to the name of the parent chain.
  • Add numbers before any alkyl groups to show the position of the alkyl groups on the parent chain.
• Naming aldehydes:

  • Identify the functional group and suffix
  • Aldehyde functional group present, the suffix is -al
  • Identify the longest chain of carbon atoms —> the longest chain contains 3 carbon atoms, the stem is propan-
  • Combine the suffix & stem to nam the compound. Aldehydes don’t need number to show the position of the carbonyl group —> it is always on group 1
• General formula —> the simplest algebraic formula of a member of a homologous series.
• Structural formula —> the minimal detail that shows the arrangement of atoms in a molecule
• Displayed formula —> the relative positioning of atoms and bonds between them
• Skeletal formula —> the simplified organic formula shown by removing hydrogen atoms from alkyl chains, leaving just a carbon skeleton and associated functional groups
• Skeletal formula:

  A skeletal formula is a simplified organic formula. You remove:

  • all of the carbon & hydrogen labels from carbon chains
  • any bonds to hydrogen atoms

  This leaves just a carbon skeleton & any functional groups
• In skeletal formulae:

  • a line represents a single bond
  • an intersection of two lines represents a carbon atom
  • the end of a line represents a -CH3 group
• Structural isomers —> compounds with the same molecular formula but different structural formulae.
• Isomers with the same functional group:

  In compounds containing a functional group, the functional group can be at different positions along the carbon chain.
• Chain isomerism —> isomers have a difference in chain length - caused by branching
• Positional isomerism —> the position of a functional group differs along a chain.
• Functional group isomerism —> the position of atoms causes a different functional group
• Radicals --> species with an unpaired electron which makes them highly reactive
• Radicals can be formed by homolytic fission:

  • Homolytic --> each atom in a bond takes one shared electrons
  • Fission --> splitting of a covalent bond
• Ultraviolet radiation has enough energy to split the covalent bonds in within molecules to form radicals

  • The dot represents an unpaired electron
  • hv represents the energy input
• Radical substitution:

  • A substitution reaction occurs when an atom/ group is replaced by another species
  • There are 3 stages of a radical substitution reaction:
  • Initiation - radical formation
  • Propagation - formation of a product & a new radical
  • Termination - reaction ends as radicals removed
• Initiation:

  • Diatomic halogen molecules can be split into halogen radicals by UV radiation high in the atmosphere
  • The pair of electrons in the bond are split up evenly to form halogen radicals
• Propagation:

  • During propagation a series of reactions help to maintain the concentration of halogen radicals
  • Step 1 : halogen radical removes an alkane's hydrogen forming an alkyl radical
  • Step 2: alkyl radical removes a halogen forming a halogen radical again
• Termination

  • The termination step involves 2 radicals reacting with each other to form a covalent bond
  • There are many possible outcomes:-
  • .CH3 + .CH3 --> C2H6
  • .CH3 + .Cl --> CH3Cl
  • .Cl + .Cl --> Cl2
• Radical reactions:

  As radicals are so reactive, the reactions are hard to control and many different products could be formed.

  The three steps of the mechanism can occur at the same time resulting in products reacting with radicals forming:

  • Longer alkane chains
  • Multiple substitutions of halogens on an alkane
• Homolytic fission:

  When a covalent bond breaks by homolytic fission, each of the bonded atoms takes one of the shared pair of electrons from the bond.

  • Each atom now has a single unpaired electron
  • An atoms or group of atoms with an unpaired electron is called a radical
• Heterolytic fission:

  When a covalent bond breaks by heterolytic fission, one of the bonded atoms take both of the electrons from the bond.

  • The atom that takes both electrons becomes a negative ion
  • The atom that does not take the electrons becomes a positive ion
• Curly arrows:

  • In a reaction mechanism, curly arrows are used to show the movement of electron pairs when bonds are being broken or made.
• Addition reactions:

  • In an addition reaction, two reactants join together to form one product.
  • In the addition reaction, a molecule is added to the unsaturated alkene, breaking the double bond , to form a single saturated compound
• Substitution reaction:

  • In a substitution reaction, an atom or group of atoms is replaced by a different atom or group of atoms
• Elimination reaction:

  • An elimination reaction involves the removal of a small molecule from a larger one.
  • In an elimination reaction, one reactant molecule forms two products