Chapter 17 Spectroscopy I Flashcards
What is the process of mass spectrometry?
The compound loses an electron to form a 1+ ion
The compound fragments
The mass spectrometer detects the mass/charge, which gives the molecular mass of the compound
What is the M+ peak?
The peak the (furthest) right of the mass spec graph, giving the molecular mass of the compound
What is important to remember when writing down mass spec fragments?
They are ions so have + charges
What is the M+1 peak?
The peaker one more than the M+ peak due to carbon 13 isotopes
Can have several peaks depending on what other compounds are present e.g chlorine has two isotopes 35 and 37
How does a mass spectrometer physically work?
Ionisation- forming 1+ ions, bombarding with electrons
Acceleration- to same KE
Deflection- by a magnetic field depending on mass
Detection of IONS only
What are the uses of Mass Spectrometers?
Identifying unknown compounds
Determine isotope abundances
Gain further information about chemical structures
Detecting banned substances such as steroids
Analysing molecules in space
Show a possible fragmentation of CH3CH2CH3+
CH3CH2+ + CH3’
Only the ion is detected, not the radical
How do you calculate the formula from percentage compositions?
Divide by molar mass
Divide moles by the lowest moles
Multiple if necessary to whole numbers or round, then multiple to molecular mass given my mass spec
How does IR affect covalent bonds?
The covalent bonds absorb IR and vibrate more
They can stretch- changing the distance between the atomic centres or bend- change the bond angle
What factors affect how much a bond vibrates?
The mass of the atoms- heavier atoms vibrate more slowly
Strength of the bond- stronger bonds vibrate faster
How does the greenhouse effect work?
UV from the sign passes through atmosphere and absorbed. Some of it is re-emitted as IR
Longer wavelength IR has the same frequency as the natural frequency of bonds of greenhouse gases so absorbed, THE BONDS ABSORB IR vibrate more
Re-emitted as radiation increasing global temperatures
What region is the fingerprint region?
Below 1500cm-1
How does IR spectroscopy work?
Beam of IR radiation, 200-4000cm-1 fired through sample
Emerging beam of light analysed
Computer plots transmittance against wave number
What are common application of IR?
Breathalysers to detect ethanol, alcohol in breath
Detecting vehicle emissions
Compared against known graphs
What factors affect the greenhouse effect?
The concentration/amount of greenhouse gases
The ability to absorb IR/ Natural frequency
Residence time of greenhouse gases
