UNIT 3 Section 9 - Further Synthesis and Analysis Flashcards
when can chromatography be used
to separate and identify the components in a mixture and purify compounds
how do the components separate at different points
Separation depends on the balance between solubility/affinity in/to the moving phase and retention by the stationary phase
what does a higher affinity for the mobile phase mean in terms of separation
move more quickly through the stationary phase and travel further so will have a larger Rf value
what does a polar stationary phase mean for mixtures
if the stationary phase is polar a polar mixture will move quicker in the mobile phase
name some examples of polar stationary phases
SiO2 and Al2O3 are regarded as polar powder
name some non- polar solvents
any alkanea
name some polar solvents for the mobile phase
water or alcohols
describe thin later chromatography
when a plate is coated with a solid and a solvent moves up the plate `
describe column chromatography
a column is packed with a solid and a solvent moves down through the column
describe has chromatography
a column is packed with a solid or with a solid coated by a liquid and a gas is passed through the column under pressure at high temperature
what does a short retention time mean
that the substance has more affinity to the mobile phase compared to the stationary phase
what are the solvents used in NMR and why do we use them
CCl4 or CDCl3
so that no protons interfere with the sample from the solvent
what is used to calibrate the spectrum in NMR
a small amount of TMS
why is TMS used to calibrate NMR
- It only gives one signal that is far away from all others that is strong as there are 12 protons in the environment
- Nontoxic
- It is inert
- Has low BP so is easy to remove from the sample
what does the structure of TMS look like
silicon bonded to 4 methyl groups
what is the x axis called on an NMR spec
chemicals shift
what does the area under a peak on NMR spec tell us
how many hydrogens are in that environment
what does each signal on an NMR spec represent
an equivalent H environment
what are the clusters of mini peaks on an NMR spec
result of spin-spin coupling with adjacent hydrogen
what makes a chemical shift greater than expected on NMR
The closer the atom to a very electronegative atom or double bond the greater the chemical shift
