Spec Flashcards
How does infrared spectroscopy work
Infrared radiation causes covalent bonds to vibrate more and absorb energy. The amount of energy absorbed by the sample is compared to that of a reference
How can Alcohols be identified in IR
A broad peak around 3450-3610cm-1
How can carbonyls be identified in IR
A sharp peak around 1700-1800cm-1
How can carboxylic acids be identified in IR
A carbonyl peak around 1700-1800cm-1 and a very broad OH peak from 2500-3300cm-1
What is the standard chemical used for chemical shift measurements in carbon-13 NMR
Tetramethylsilane TMS, which is non toxic and inert, with all four carbons in the same environment
What four pieces of information does H NMR spec give
Number of proton environments, types of environments, integration-the number of protons that give each signal, splitting-the number of inequivalent protons on an adjacent carbon atom
What is the issue with labile protons in H NMR
(Protons that are bonded to an electronegative atom)
Peaks can appear over a wide range of shift values, the signals are broad and obscure others due to H bonds, there is usually no splitting pattern
Deuterium exchange
If say methanol is dissolved in D2O then the alcohol protons will exchange with D instead of H, which will make the OH peak disappear as the D nucleus is excited in a different frequency range.
What determines the separation in chromatography?
The strength of interaction with the stationary phase.
What is the stationary phase in TLC?
A thin layer of solid absorbant (usually silica gel or alumina) coated on a flat support made of glass, plastic, or aluminium.
What is the TLC mobile phase?
A liquid mixture of organic solvents, will depend on particular reaction.
What are three limitations of TLC?
Similar components will have similar Rf values.
Unknown compounds have no Rf value to compare against.
It can be hard to find the right solvent to properly separate all of the different components.
What is the stationary phase in gas chromatography?
A thin layer of non-polar high-boiling-point liquid coated on the inside of capillary tubing, which remains there due to capillary action.
What is the GC mobile stage?
Gas, usually helium or nitrogen.
Why does separation occur in GC?
The relative levels of interaction with the stationary phase of different compounds, leading to differing retention times.
