4.8 - Organic Synthesis and Analysis

Mass spec

• Highest m/z = Mr

• Use others to find fragments using parts of Mr value

• Add a positive charge to all species

• Give species and value

Infrared spectroscopy

• Give bond and frequency

• Focus on bonds in functional group

• Absence of a bond can be useful

C NMR

• Number of peaks => number of carbon bonding environments

• Shift value => nature of carbon bonding environment

Low resolution H NMR

• Number of peaks => number of H bonding environments

• Shift value => nature of H bonding environment

• Ratio of peak areas => relative number of equivalent hydrogen nuclei in each bonding environment

Reflux

• Heating volatile organic compounds

• Needed as reactants would evaporate before reaction is complete + products (if volatile) would also be lost

Filtration

• Filtration under suction or reduced pressure = better at removing an insoluble solid from a liquid than paper filtration

Distillation

• Simple distillation = separate a mixture of a soluble solid from the solvent

• Fractional = separate a mixture of miscible liquids with different boiling temperatures

• Steam = seperate insoluble liquids from a reaction mixture

• Reduced pressure can be used if the substance decomposes when heated. This is used to lower the Tb

Simple distillation

• Simple distillation = separate a mixture of a soluble solid from the solvent

Fractional distillation

• Fractional = separate a mixture of miscible liquids with different boiling temperatures

Steam distillation

• Steam = seperate insoluble liquids from a reaction mixture

Distillation at a reduced pressure

• Reduced pressure can be used if the substance decomposes when heated. This is used to lower the Tb

Explain the process of recrystallisation

Purify a solid. Solvent chosen is one that dissolves more of the solid when it is hot than when it is cold

• Dissolve the solid in the minimum volume of hot solvent

• Filter hot if required to remove any in dissolved solid which would be an impurity

• Cool the hot solution

• Filter under suction/reduced pressure to remove the solid

• Wash the solid with ice cold solvent

• Dry to a constant mass

• Determine the purity of the solid by testing its melting temperature

Melting temperature and purity

• Pure = has an exact melting temperature

• Impurities = melting temp is lowered and solid will melt over a range of temps below the one given

Addition polymerisation

One type of unsaturated monomer

Polymer is only product

Condensation polymerisation

Two types of monomer

Polymer and small molecules produced

2 types

2 examples of condensation polymers

Polyamides

Polyesters

Polyamides

Diamine + dicarboxylic acid

Polyesters

Diol + dicarboxylic acid

Formation of PET

Formation of Nylon-6

Formation of Nylon-6,6

High Resolution H NMR

• Number of peaks => number of H bonding environments

• Shift value => nature of H bonding environments

• Ratio of peak areas => relative number of equivalent H nuclei in each bonding environment

• Splitting pattern of the peaks => (n+1) rule where a peak splits into n+1 parts where n= total number of H nuclei on neighbouring C atoms

  • 0 atoms = singlet peak

  • 1 = doublet

  • 2 = triplet

  • 3 = quartet

Thin layer chromatography

• SP = surface of a thin glass/plastic plate

• Spot of mixture placed about 10mm from bottom edge

• Place stood or suspended in about 5mm of solvent

• Solvent travels up plate

• Components separate

• Components identified from Rf (retardation factor)

Stationary phase

• The stationary phase is the part of the chromatography that remains in place as the process occurs. In paper chromatography, this is the paper, and in thin layer chromatography, this is the silica or aluminium oxide on the TLC plate.

Mobile phase

• The mobile phase is the part of the chromatography that moves as the process occurs. In both paper and thin layer chromatography, this is the solvent being used.

Rf value

Distance moved by component/distance moved by solvent front

Gas liquid chromatography

• Organic mixtures

• Components identified from time taken for component to reach detector (retention time)

• Integrate area under pan in the recording of the detector = estimate of amount of component present

High performance liquid chromatography

• Mixture forced through a column of the SP (small particles in a small diameter tube)

• Pump a liquid (MP) through

• Components identified by retention times

• Areas under peaks by integration