C17 - Spectroscopy Flashcards
What is a mass spectrometer?
Detects mass to charge ratio of the molecular ion giving molecular mass of the compound
What is a molecular ion?
Positive ion formed in mass spectrometry when a molecule loses an electron
M+
How do you identify the M+ peak?
Clear peak at the highest m/z value on the right hand side
Why do you see a small peak one unit after the M+ peak?
M+1 peak
1.1% of carbon is present as the carbon-13 isotope
What is fragmentation?
Process in mass spectrometry that causes positive ion to split into smaller pieces (cation and radical)
What is a fragment ion?
Ions formed from the breakdown of the molecular ion in a mass spectrometer
What are the other peaks on a mass spec?
Fragment ion peaks
How molecules absorb IR radiation?
Atoms joined by covalent bonds which vibrate naturally
Bonds absorb IR
What does absorbing IR do to bonds?
Make the bend or stretch more
What does the amount that a bond bends or stretches depend on?
-Mass of the atoms: heavier atoms vibrate slower
-Strength of the bond: stronger vibrate faster
What radiation can a bond absorb?
Frequency which is the same natural frequency of the bond
Explain the greenhouse effect
IR radiation absorbed by Earth’s surface
Longer wavelength IR radiation re-emitted
H2O, CO2 and CH4 absorb it
Eventually they re-emit it, increasing temperature of Earth’s atmosphere
How does IR spectroscopy work?
1) Sample placed under IR spectrometer
2) Beam of IR 200-4000cm^-1 passed through sample
3) Molecule absorbs some frequencies
4) emerging beam of radiation analysed to identify frequencies that have been absorbed
5) IR spectrometer connected to computer that pots graph of transmittance against wave number
What is the fingerprint region?
Below 1500cm^-1
Unique peaks
IR spec of alcohol
Peak at:
3200-3600 O-H
1000-1300 C-O
IR spec of aldehyde/ketone
Peak at:
1630-1820 C=O
closer to 1700
IR spec of carboxylic acid
Peak at:
1630-1820 C=O (broad peak)
closer to 1700
2500-3330 O-H
1000-1300 C-O
