4.8 Organic Synthesis & Analysis Flashcards
Describe thin layer chromatography
- used to monitor when desired products are produced in a reaction
- stationary phase is a thin layer of absorbent
- mobile phase is a liquid solvent
- components separated by adsorption
Rf equation
Distance moved by component
———————————————
Distance moved by solvent
What are the limitations of Rf values?
- different Rf depending on solvent
- time consuming
- similarity in functional groups
- unknown compounds don’t have an Rf value
- difficult to find ideal solvent
Describe gas chromatography
- separate gases with low boiling points
- use capillary column
Define retention time
Time taken from inlet to detector
How does GC-MS work?
- separate compounds using GC and identify using MS
What is the molecular ion peak?
Highest peak aka the Mr
What does C-H peak above 3000cm mean?
Unsaturated (double bonds)
What does C-H peak below 3000cm mean?
Saturated (no double bonds)
What is NMR and how does it work?
- nuclear magnetic resonance
- nuclei have magnetic spin due to uneven number of nucleons
What factors influence NMR?
- nuclear shielding
- chemical shift
Explain what is meant by nuclear shielding
- magnetic field felt by nucleus is affected by strength of the applied magnetic field
- electron withdrawing atoms leave the atom exposed to a stronger field
—> any atom more electronegative than carbon
Explain what is meant by chemical shift
- place in which nucleus absorbs energy
- measured relative to TMS peak which is always at 0
What solvent is appropriate for carbon NMR?
- CDCl3
- 2H isotope doesn’t show in the NMR as it has an even number of nucleons
How can impurities be identified by melting point?
- impruirites cause melting point to be lower than expected
- pure samples have very sharp melting points that can be compared to a literature
Describe addition polymers
- produced from alkenes
- non-polar so very unreactive
Describe polyamides
- type of condensation polymer
- carbon and amines
- amine linkage as water is removed
Describe polyesters
- carboxylic acids and alcohols
- ester linkage
Are condensation or addition polymers stronger?
- condensation generally stronger
—> chain contains polar bonds so permanent dipole-dipole forces and hydrogen bonds exist between polymer chains - addition polymers are held by VdW
What does the area under peaks in H NMR tell you?
- ratio of hydrogen atoms in the diff environments
How do you determine number of peaks on a H NMR?
- number of hydrogens on the adjacent carbon plus one
