Chromatography and spectroscopy

What is chromatography used for?

• to separate individual components from a mixture of substances

State the 2 phases which chromatography has and explain them?

• stationary phase→ doesn’t move, normally a solid

• Mobile phase→ moves, normally a liquid or gas

What does TLC indicate?

• how many components are in a mixture

Define adsorption?

• the accumulation of molecules on a surface

State the formula to calculate Rf value?

What is gas chromatography useful for?

• separating and identifying volatile organic compounds present in a mixture

State them mobile phase of gas chromatography?

• an inert gas carrier such as helium or neon

Define retention time?

• the time taken do each component to travel through the column of the gas chromatograph

What is each component detected as on a gas chromatogram?

• a peak

state the 2 pieces of information which can be obtained from a gas chromatogram?

• Retention times→ can be used to identify the components present in the sample by comparing retention times for known components

• Peak integrations(the area under each peak)→ can be used to determine concentrations of components in the sample

What can the concentration of a component in a sample be determined by?

• External calibration

• comparing its peak integration with values obtained from standard solutions

State the chemical test for an alkenes and the observation?

• chemical test= add bromine water drop wise

• Observation = bromine water recoloured from orange to colourless

State the chemical test for haloalkanes and the observation?

• Chemical test=silver nitrate and ethanol and warm water bath

• Observation=

  • chloroalkane, white precipitate

  • bromlalkane, cream precipitate

  • Iodoalkane, yellow precipitate

State the chemical tests for carbonyls and the observation?

• Chemical test= 2,4 DNP

• Observation= orange precipitate

State the chemical test for aldehydes and the observation?

• Chemical test= tollens resent and warm

• Observation = silver mirror

State the chemical tests for a primary and secondary alcohol and aldehyde and the observation?

• Chemical test= K2Cr2O7 and heat

• Observation = colour change from orange to green

State the chemical test for a carboxylic acid and the observation?

• Chemical test= aqueous sodium carbonate

• Observation = effervescence

Define NMR?

• nuclear magnetic resonance

Define chemical shift?

• the difference between the resonance frequency of a nucleus and that of a standard reference compound, measured in parts per million (ppm).

What is used as the standard reference chemical agains which all chemical shifts are measured?

• TMS- Tetramethylsilane

State the chemical shift value of TMS?

• 0 ppm

why are deuterated solvents used in NMR spectroscopy?

• prevents interference from solvent hydrogens in the ¹H NMR spectrum.

State the 2 pieces of information which carbon -13 NMR spectroscopy provides?

• the number of different carbon environments present from the number of peaks

• They types of carbon environment present from the chemical shift

State the 4 pieces of information which proton NMR provides?

• the number of proton environments

• The chemical shift- types of protons environment

• Integration data- the relative numbers of each type of proton

• The number of non equivalent protons adjacent to a given proton from the spin spin splitting pattern

Define equivalent protons?

• protons which absorb the same chemical shift increasing the size of the peak

Define non equivalent protons?

• protons which have different chemical environments and absorb different chemical shifts

What is the area under each peak known as for proton NMR?

• the integration trace

What are the splitting patterns of a proton NMR peak caused by?

• the protons spin interacting with the spin states of nearby protons that are in different environments

What is the splitting of a main peak into sub peaks called?

• spin spin coupling/spin spin splitting