Lab Techniques
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What is the use of NMR?
determining the structure of a given molecule
What is the principle of NMR? (a.k.a. how does it work?)
EWG surrounding hydrogen causes chemical shift to appear downfield EDG surrounding hydrogen causes chemical shift to appear upfield
What is the approach to using NMR?
• Count hydrogen environments • Order environments by electron density (chemical shifts) • Find splitting patterns based on neighbouring hydrogens • Find number of hydrogens (integral trace) • Calculate degree of unsaturation
What is the use of IR?
identifying specific functional groups
What is the principle of IR? (a.k.a. how does it work?)
polar bonds vibrate at characteristic frequencies when exposed to infrared radiation
What functional groups correspond to the ~3000 cm^-1 region of the IR spectrum?
CH, OH, NH
What functional groups correspond to the ~1700 cm^-1 region of the IR spectrum?
C=O (carbonyl) sharp peak
What is the use of mass spectroscopy?
Determining molecular weight and/or molecular formula.
What is the principle of mass spectroscopy? (a.k.a. how does it work?)
molecules are bombarded with electrons –> breakdown into small fragments –> fragments accelerated through magnetic field based on its mass to charge ration (m/z)
What is the approach to using mass spectroscopy?
parent peak (right most) = highest mass = molar mass of the original sample base peak (largest peak) = most stable and common cation fragment
What is the use of UV spectroscopy?
Determining extent of pi conjugation
What is the principle of UV spectroscopy?
conjugated molecules can absorb energy in the UV region
What is the approach to UV spectroscopy? (i.e. how do you interpret conjugation based on the spectroscopy results?)
greater the amount of conjugation, greater the wavelength of maximum absorption
What is the use of size-exclusion chromatography?
Determining particle sizes
What is the principle of size-exclusion chromatography?
large particles elute faster than small ones
What is the approach to size-exclusion chromatography?
compare molecules based on size (often, molar mass)