Into Organics

Representation of Organic Molecules
  • The Empirical Formula gives the least detail. E.g. The empirical formula of ethane (C2H6) is CH3.
  • The Molecular Formula shows the actual numbers of each type of atom in a molecule. E.g. Ethane is C2H6.
  • The Structural Formula tells us about the atoms bonded to each carbon atom. Carbon-Carbon double bond (C=C) are shown in the formula the following way. E.g. Propene is CH3CH=CH2.
  • The Displayed Formula is the actual shape of the molecule, showing all the atoms and bonds. A simplified version of the displayed formula is the skeletal formula, from which C atoms and H atoms are removed and only the bonds and other atoms are left.
Bonding in organic molecules Sigma Bond – By forming single covalent bonds with four other atoms, a carbon atom can gain the electronic configuration of the noble gas, neon. The single covalent bonds are known as sigma bonds. The shape of the molecule is tetrahedral, and the bond angle is of 109.5Pi Bond – A C=C double bond, as found in alkenes such as ethene, is made up of a sigma bond, and a pi bond. The Pi bond makes a molecule more reactive. The C atoms involved in a double bond are surrounded by three pairs of electrons. The bond angle is of about 120 degrees.
Structural Isomerism Compounds with the same molecular formula but different structural fromulae are called structural isomers.There are three types of structural isomerism:

  1. Position isomerism – The position of the functional group varies
  2. Functional group isomerism – Different functional groups are present
  3. Chain Isomerism – Molecules differ in the structure of their carbon ‘skeleton’
Stereoisomerism Compunds whose molecules have the same atoms bonded to each other but with different arrangements of atoms in space.There are two types of stereoisomerism.

  1. Cis-Trans Isomerism
  2. Optical Isomerism – 2 Different molecules. Put close together they look like mirror images.The Carbon in the middle is called a Chiral Centre.

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