Naming and isomerism

• Homologous series


  A series of organic compounds with the same functional group and similar chemical properties, where each member differs from the next by a CH2 group
• Functional group


  A specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule
• Prefix


  A part added to the beginning of a word to modify its meaning
• Suffix


  A part added to the end of a word to modify its meaning
• Aldehydes


  • -al
  • formyl-
• Ketones


  • -one
  • oxo-
• Carboxylic acids


  • -oic acid
• Nitriles


  • -nitrile
  • cyano-
• Amines


  • -amine
  • amino-
• Esters


  • -yl -oate
• Acyl chlorides


  • -oyl chloride
• Amides


  • -amide
• Acid anhydrides


  • -oic anhydride
• When compounds contain more than one functional group, the order of precedence determines which groups are named with prefix or suffix forms. The highest precedence group takes the suffix (and the lowest number on the carbon chain), with all others taking the prefix form. However, double and triple C-C bonds only take suffix form.
• Order of priority highest first

  • Carboxylic acids
  • Carboxylic acid derivatives
  • Nitriles
  • Aldehydes
  • Ketones
  • Alcohols
  • Amines
  • Alkenes
  • Halogenoalkanes
• Amines


  These end in -amine. There is, however, rather confusingly two ways of using this suffix. The exam board tend to use the common version where the name stem ends in -yl propylamine. Another version of the same chemical is propan-1-amine. (This is used in the same way as naming alcohols)
• Amines with another priority functional group

  The prefix amino is used
• Secondary amines


  If the amine is secondary and has two alkyl groups attached to the nitrogen, then each chain is named and the smaller alkyl group is preceded by an -N which plays the same role as a number in positioning a side alkyl chain
• Tertiary amines


  Similar rules apply, and each alkyl side group is given an N
• Aldehydes


  An aldehyde's name ends in -al. It always has the C=O bond on the first carbon of the chain so it does not need an extra number. It is by default number one on the chain
• Ketones


  Ketones end in -one. When ketones have 5C's or more in a chain then it needs a number to show the position of the double bond. E.g. pentan-2-one
• Carboxylic acids


  These have the ending -oic acid but no number is necessary for the acid group as it must always be at the end of the chain. The numbering always starts from the carboxylic acid end
• Dioic acids


  If there are carboxylic acid groups on both ends of the chain then it is called a -dioic acid
• Ketones with carboxylic acid or aldehyde

  The prefix oxo- should be used for compounds that contain a ketone group in addition to a carboxylic acid or aldehyde
• Esters


  Esters have two parts to their names. The bit ending in -yl comes from the alcohol that has formed it and is next to the single bonded oxygen. The bit ending in -anoate comes from the carboxylic acid. (This is the chain including the C=O bond)
• Acid anhydrides


  This is called ethanoic anhydride. It is ethanoic because it is two ethanoate groups joined together.
• Acyl chlorides


  add -oyl chloride to the stem name
• Amides


  Add -amide to the stem name
• Secondary and tertiary amides

  The smaller alkyl group is preceded by an -N which plays the same role as a number in positioning a side alkyl chain
• Nitriles


  These end in -nitrile, but the C of the CN group counts as the first carbon of the chain. Note the stem of the name is different: butanenitrile and not butannitrile.
• Structural isomers: same molecular formula different structures (or structural formulae)
• Functional group isomers: Compounds with the same molecular formula but with atoms arranges to give different functional groups
• Stereoisomers


  Stereoisomers have the same structural formulae but have a different spatial arrangement of atoms
• Geometrical (E-Z) isomerism


  One type of stereoisomerism
• Optical isomerism


  Another type of stereoisomerism
• Asymmetric carbon


  A carbon atom that has four different groups attached
• Enantiomers


  Two compounds that are optical isomers of each other
• Racemate


  A 50/50 mixture of the two optical isomer enantiomers
• Optical isomers have similar physical and chemical properties, but they rotate plane polarised light in different directions. One enantiomer rotates it in one direction and the other enantiomer rotates it by the same amount in the opposite direction.
• A racemic mixture (a mixture of equal amounts of the two optical isomers) will not rotate plane-polarised light.