lab Flashcards
1
Q
general IR patterns
A
- stronger bonds will vibrate at a higher frequency
- smaller atoms will vibrate at a higher frequency
***based on Hooke’s law
2
Q
what to look for in melting point data
A
- accurate melting points are small range close to lit value
- inaccurate melting points from impurities are large range and lower than lit value
3
Q
crystals in a pure sample are…
A
- stable
- well-ordered
- low Gibbs energy
4
Q
reflux
A
- solution is heated to its boiling point
- vapor produced is constantly cooled back into liquid form
- allows reaction to run while being heated, but no reactants or products are lost from evaporation!!
5
Q
extraction
A
- separating aqueous and organic layer (2 immiscible liquids)
- more small extractions are better
6
Q
sublimation
A
solid goes to gas without melting–purification process!
7
Q
using a cold finger to purify
A
- crystals sublime (go straight to gas)
- gas product then re-solidifies on the cold finger
8
Q
percent recovery vs percent yield
A
- percent recovery is for isolations
- percent yield from synthesis
9
Q
general principles of chromatography
A
- components are either more in stationary or mobile phase
- phase depends on polarity of components (will be in phase that matches their polarity)
10
Q
TLC specifics
A
- stationary phase (adsorbent): usually silica on a plate, does not move
- mobile phase (eluent): liquid that moves across plate
*stationary phase is usually the more polar phase!
11
Q
Rf values
A
- for TLC; distance traveled by compound of interest divided by distance traveled by solvent front
- values closer to 0 indicate compound is more polar
- values closer to 1 indicate compound is less polar
12
Q
shielding in NMR
A
- shielding: more electrons near the nucleus decrease the magnetic field sensed by the nucleus
- deshielding: alternatively, electron-withdrawing atoms will increase magnetic field sensed by nucleus
- more deshielded nuclei come into resonance at a higher frequency (more downfield, or left)
