Homologous Series

• Homologous series - serious or family of similar organic compounds that have similar features and chemical properties due to them having the same functional group, and they have the same general formula

  • functional group - an atom or group of atoms that are bonded in a specific arrangement that is responsible for the characteristic reactions of each member of a homologous series
• • Table of compounds & their function groups (Make sure you can identify the functional group for each homologous series)

  A) alkane

  B) alkene

  C) alcohol

  D) carboxylic acid

  E) amine

  F) ester

  
• Alkane- single covalent bonds between carbon atoms
• Alkenes - double covalent bonds between carbon atoms
• Alcohol - only has OH singlely covalently bonded to carbon
• Carboxylic acid - has a carbon double bond to oxygen and a single caovalent bond to OH
• Esters - has carbon with a double covalent bond to an oxygen atom and a single bond with an oxygen
• Amines - has nitrogen and 2 hydrogen singlely covalent
• General formulae - tells you the composition of any member of a whole homologous series of organic compound

  • e.g. all alkanes have CnH2n+2, n = the number of carbon atoms - tells you that however many carbon atoms there are in the alkane, doubling this number and adding two will give you the number of hydrogen atoms present in the alkane
• General formulae can be used to work out the formula of a compound from different homologous series if the number of carbon atoms present is known
• • General formula of common homologous series (Make sure you learn the general formula for each homologous series)

  A) alkanes

  B) alkenes

  C) alcohols

  D) carboxylic acids

  
• All members of a homologous series have:

  • The same general formula
  • Same functional group
  • Similar chemical properties
  • Gradual change in their physical properties, such as melting and boiling point
  • The difference in the molecular formula between one member and the next is CH
• As you go up the homologous series in order of the number of carbon in the chain, chain length and relative molecular mass of the molecule increases, the physical properties change

  • the melting and boiling points increase
  • compounds change from gas → liquid → solid
• Number of carbons and corresponding state

  • <4 = gas
  • 5-16 = liquid
  • 16+ = solid