Organic Analysis: Mass And IR Spec Flashcards
How does a Mass Spectrometry work?
Vaporisation
Ionisation (Always positive ions)
Acceleration by an electrical field
Deflection by magnetic field
Detection
Where does infrared spectra work?
IR is absorbed by any molecule who’s dipole can change (i.e: Must have polar BONDS)
IR absorption causes bonds to increase in vibration, so they bend or stretch
How does IR Spec follow a reaction?
Can monitor the progress of an organic reaction
Changing of bonds means the certain peaks will decrease on the graph and form newer peaks
Can monitor the rate as the peak height is proportional to the concentration of the bond so graph can be plotted at regular intervals to find the rate
How does a Carbon-13 Nuclear Magnetic Resonance Spectroscopy work?
C-13 isotopes show signal and shows position of C-13 atoms
Measured against reference compound Tetramethysilane (TMS)
height is NOT proportional to number of carbon atoms present
Diff chemical environment give resonances at different chemical shifts
Why is TMS used?
Non-toxic
Does not react with sample
Easily separated from sample molecule due to low boiling point
One, strong absorption peak on HNMR spectrum
Features of HNMR Spectrum
Area under each peak gives information about the number protons (hydrogen) in a particular environment
Height proportional to intensity/absorption of protons
Shows peaks of Hydrogen nuclei with different neighbouring atoms —> diff chemical environment
Same chemical environment = one peak
Features of low res HNMR
Molecular environment of each H nuclei
Strengths of absorption are proportional to number of equivalent H atoms —> measured by the area underneath each absorption peak
Features High Res HNMR
Number of peaks a signal splits into = n+1
N = number of protons on the adjacent carbon atom
Splitting relative intensity = Pascal’s triangle
OH doesn’t cause splitting
OH identified by running NMR spec with heavy water as D replaces H in OH group
