Synthetic routes, Mass spectrum and IR Flashcards
What happens when a molecule absorbs infrared radiation?
It makes the covalent bond vibrate more in a stretching or bonding motion where it can then absorb energy
What factors affect the amount of vibration of a bond?
- Bond strength
- Bond length
- Mass of each atom in a bond
How does infrared spectroscopy work?
The IR radiation is passed through a sample where the different type of bonds absorb the radiation in different amounts. These varying amounts of absorbance are measured and recorded.
What are the 2 peaks that must be present to identify a substance as carboxylic acid?
- Very broad peak O-H groups
- Sharp peaks C=O
What happens inside a mass spectrometer?
- Organic compounds is vaporised and passed through the spectrometer where a high voltage is passed
- This causes electrons to be removed from the atoms (they are ionised) leaving +1 charged ions
- Energy causes vibrations and the bonds weaken and fragment
Is fragmentation predictable?
No, because it can happen anywhere in the molecule
What is the m/z value of CH3+?
15
What is the m/z value of OH from an alcohol?
17
What is the m/z value of C2H5+
29
What is the m/z value of C3H7+
43
What are 2 advantages of using mass spectrometry?
- Cheap
- Small quantities of sample required
What is the main disadvantage of using mass spectrometry?
The sample is completely destroyed
How do you convert an alkene to an alkane?
H2 and a Ni catalyst
How do you convert an alkene to a haloalkane?
Hydrogen halide
How do you convert an alkane to a haloalkane?
Halogen/UV
How do you convert an alcohol to a haloalkane?
Sodium halide and H2SO4
How do you convert an alcohol to an alkene?
Dehydration, conc H2S04
How do you convert a haloalkane to an alcohol?
NaOH (aq) and reflux
How do you convert an alkene to an alcohol?
H3PO4 and steam (H2O)
What is the process of purifying organic products?
- Pour liquids into separating funnel and allow them to separate
- Add water to aq later and add a flask under and collect the bottom layer
- Collect the final layer
When purifying an organic product what are the 2 layers and how can you make a distinction between them?
There is an aq layer and an organic layer, adding water will make the aq layer bigger
How do you purify a impure product that may contain acid?
Add aq sodium carbonate and shake and open tap slowly to release gas
In a mass spectrometer how is a molecular ion represented?
- M+
- The peak with the highest m/z ratio
How might you dry an organic product?
- Add organic layer to a flask
- Add a drying agent (anhydrous sodium sulfate)
- Place a stopper to avoid evaporation
- Decant liquid into a round bottomed flask
Give an everyday use for infrared spectroscopy
Breathalysers
