Module 6

• Where might the synthesis of organic compounds with more carbon atoms be important?

  The pharmaceutical industry
• What is the nitrile group?

  -CN
• Name the reagents and conditions to form nitriles from haloalkanes

  Sodium cyanide/ potassium cyanise

  Ethanolic solvent
• Name the general equation for the formation of nitriles from haloalkanes.

  
  

  Use X to represent a halogen and R to represent a carbon chain

  RX + NaCN = RCN + NaX
• What type of reaction is the formation of nitriles from haloalkanes?

  Nucleophilic substitution
• What types of nitriles can be made from aldehydes and ketones?

  Hydroxy nitriles
• What is the equation for aldehydes being turned into hydroxy nitriles?


  aldehyde + HCN = hydroxy nitrile
• What type of reaction is the formation of a hydroxy nitrile from an aldehyde or ketone?

  Nucleophilic addition
• What can nitriles be reduced into?

  Amines
• What is the equation and catalyst for the formation of an amine from a nitrile?

  Nitrile + 2H2 = Amine

  Nickel catalyst
• What can the hydrolysis of nitriles form?

  Carboxylic acids
• Name the equation and conditions for the hydrolysis of nitriles

  Nitrile + HCl + 2H2O = carboxylic acid + NH4Cl

  
  

  Dilute aqueous acid
• Name two ways to increase carbon-carbon bonds using benzene rings.

  The alkylation and acylation of benzene rings
• What is chromatography used for?


  Used to seperate mixtures of substances into their components.
• Name the two types of chromatography

  Thin layer chromatography and gas chromatography
• What is the stationary phase in TLC and in GC

  TLC: a solid

  GC: a liquid/solid supported on a solid
• What methods do TLC and GC use for seperation?

  GC: partition/ relative solubillity

  TLC: adsorption
• What is the formula for Rf values?

  distance travelled by component/ distance travelled by solvent
• What is the Rf value used for?

  The Rf value is specific for a particular component under the same conditions so you can identify the component.
• How does adsorption work in thin layer chromatography?

  The solvent travels up the plate by capillary action and dissolves the compounds in the spot. The compound present is carried up the plate with the solvent.
• What does the speed of components travelling up the plate depend on?

  1. The solubility of the compound: the attraction between the molecules of the compound and the solvent

  2. How much the molecules adsorbs onto the stationary phase
• What is the structure of silica gel?

  Silicon atoms joined via oxygen atoms, with the surface silicon atoms attached to OH groups
• Why can silica gel act as a stationary phase?

  The surface of silica is very polar because of the OH bond so it can form hydrogen bonds. Compounds which can hydrogen bond then adsorb to the surface of silica more firmly than compounds that cant. Therefore it cant travel as far with the solvent.
• What is the use of TLC in organic chem?

  Organic chemisa can monitor the progress of reactions that are being tried for the first time. You can monitor the reaction time in almost real time.
• What do the two different types of gas chromatography use?

  1. inert solid support and inert gas

  2. mobile: gas, stationary: high boiling point liquid adsorbed onto an inert solid
• What is relative solubility?

  How soluble the substance is in the stationary phase compared to the mobile phase
• What is the retention time?

  The time taken for a compound to travel through the column to the detector from the point of injection
• What two things are considered when looking at a gas chromatogram?

  1. Retention times

  2. Area under the peaks
• Why might a substance have a short retention time?

  If it is more soluble in the gas phase
• Why might a substance have a long retention time?

  If it is more soluble in the stationary phase
• What can the retention times be used for?

  Identify the compounds by comparing with retention times of pure, known samples.
• What would the area under the peaks on gas chromatogram show?

  The relative amounts of each compound in the sample
• Name some limitations of gas chromatograms

  1. Reference retention times are impossible when dealing with unknown substances

  2. Retention times are dependent on temp, pressure, choice of gas and invidiual machine so it can vary

  2. Similar compounds have similar retention times or Rf values
• What is benzene at room temp?

  A colourless liquid
• What are arenes?


  Compounds which contain unsaturated rings with delocalised electrons within the ring
• What is the formula of benzene?

  C6H6
• What was Kekule's model of benzene?

  A six membered ring with alternating double and single bonds
• Why was Kekules model viewed as sensible?

  It was consistent with the formula and simple valency rules
• Explain the evidence which disproved Kekules model.

  1. C=C bonds should decolourise bromine but benzene doesnt react with bromine water at room temp

  2. The carbon carbon lengths in benzene are the same and a value between the length of a double bond and a single bond instead of alternating

  3. When benzene is hydrogenated, it produces 152kJmol^-1 less energy than 3 double bonds being hydrogenated so its more stable.
• Describe the structure of benzene.

  Its a hexagonal ring with each carbon bonded to two other carbons and a hydrogen by sigma bonds. There are 6 electrons in a delocalised pi system since each orbital is in an overlapping p orbital.