Spectroscopy Flashcards
What happens to an organic compound in a mass spectrometer?
it loses an electron and forms a positive ion - the molecular ion
What does a mass spectrometer detect?
the mass-to-charge ratio (m/z) of the molecular ion which gives the molecular mass
What is the molecular ion?
the positive ion formed when a molecule loses an electron
How do you determine the molecular mass from a mass spectrum?
the molecular ion peak is the largest no. peak
What is the symbol for the molecular ion peak?
M+
What is the M+1 peak?
a very small peak after M+ peak due to Carbon 13 or other isotopes
What is fragmentation?
in the mass spectrometer, some molecular ions break down into smaller pieces called fragments
What does fragmentation break a molecular ion up into?
a fragment ion and a radical
What is the m/z value of CH2OH+ fragment ion?
31
What is the m/z value for CH3+?
15
What is the m/z value for C2H5+ fragment ion?
29
What is the m/z value for C3H7+ fragment ion?
43
What is the m/z value for C4H9+ fragment ion?
57
What is the m/z value for CH3CH2O+ fragment ion?
45
How does infrared spectroscopy work?
molecules can absorb infra-red radiation
the energy that is absorbed causes the covalent bonds in the molecule to vibrate
What does the amount a bond streches or bends depend on?
the mass of the atoms in the bond = heavier—> slower vibration
the strength of the bond = stronger —-> faster vibration
How does global warmbing occur due to IR radiation?
greenhouse gases absorb IR radiation because it has the same natural frequency of their bonds
the vibrating bonds re-emit this energy as radiation
resulting in increasing the temp of the earth
What is infrared spectroscopy used for?
identifying the functional groups present in organic molecules
What does an infrared spectrum show?
the frequencies that have been absorbed by the bonds
What is the fingerprint region?
peaks below 1500 wavenumber - (dont need to indentify these peeks)
What does an OH alchohol bond peak on infrared spectrum look like?
tall and broad, no spiking
What does a C-H bond look like on an infrared spectrum?
small spikes
What does a caroxyl OH infrared peak look like?
broad but has C-H spikes on the right side
What is the application of infrared spectroscopy?
used to identify pollutants - CO, CO2 and hydrocarbons
breathalysers for the presence of ethanol
traces of drugs
water and air quality monitoring - environmental pollutants
What is element analysis?
use of % composition data to determine the empirical formula
What is mass spectrometry?
use of the molecular ion peak from a mass spectrum to determine the molecular mass; use of fragment ions to identify sections of a molecule
What is infrared spectroscopy?
use of absorption peaks from an infrared spectrum to identify bonds and functional groups present in the molecule
Why is it important to maximise both atom economy and % yeild in industry?
- high atom economy means that there is less/ no waste
- high % yield means that raw materials are converted into desired products with minimum loss of materials
What issues need to be considered when trying to maximise atom economy and % yield in industrial processes?
the cost of production = energy for heat
the toxicity of the reactant/ byproducts may be too risky to carry out the reaction
What happens to molecules when they absorb IR radiation?
the bonds in the molecules vibrate
What effect does CO2 and methane absorbing IR have on the environment?
it delays the escape of IR radiation by the earth into space = warms the atmosphere = greenhouse effect
How has the conc of methane in the atmosphere risen?
intensive farming
How has the conc of CO2 in the atmosphere risen?
burning fossil fuels
What can be done to address global warming?
more efficient energy use = better insulation in homes
find alternative fuels = wind, solar, nuclear
How is a C13 NMR formed?
C13 nuclei in different environments typically absorb slightly different energies, each compound containing carbon has a characteristic NMR spectrum
What does the number of peaks on a C13 NMR represent?
the number of carbons with different environments in the molecule
if 2 or more carbons are equivalent as a reult of symmetry they will only produce 1 peak
What is chemical shift?
a measure of the energy gap between spin states for C13/ H1 nuclei in different environments
What molecule sets the NMR spectrums to 0?
tetramethylsilane - Si(CH3)4
completely symmetrical = all Cs and Hs are in the same environments
What should you do when 2 proton environments are applicable on the data sheet?
use the one with the bigger chemical shift to make the prediction
On H1 NMR what is the area of the peak represent?
the number of protons that contribute to that peak - they can be simplifed ratios
How do you find the peak area on a H1 NMR when an intergration is given?
measure the intergration heights with a ruler
What causes splitting in H1 NMR?
the energy gap between neighbouring protons
How do you calculate how many times a peak will split on H1 NMR?
n + 1
n = the number of adjacent Hs that are in different environments
What proton peaks never split?
OH peaks
What is deuterium?
2H - an isotope of hydrogen
What is a D2O shake?
NH and OH peaks disappear of the original spectrum when D2O is added to the sample
How would you identify OH and NH peaks on H1 NMR?
- run the normal spectrum - OH and NH peaks will be visible, estimate their peaks from chemical shift
- add D2O to the sample and run the spectrum again
the OH and NH peaks will dissapear, the other peaks are unaffected
What solvents need to be used for H1 NMR?
solvents that dont contain any protons
eg. D2O and CCl4, CDCL3
deuterated solvents
What does the degrees of unsaturation tell you?
the no of double bonds or rings present in a molecule
What is the equation for DOU?
2n +2 - H / 2
2n+2 = no of Hs if it was an alkane
H = no of actual Hs present
What is the equation for the DOU if Nitrogen is present?
2n +2 - H + N / 2
N = the no of nitrogens present in the molecule
