Module 4 - Synthetic Routes Flashcards
(19 cards)
describe the relationship between IR radiation and molecules
-all molecules absorb IR light
-the IR light makes the bonds in a molecule vibrate
what does the bond vibration in IR spectroscopy depend on
1- bond strength
2- bond length
3- mass of an atom at either end of the bond
what is used instead of frequency when using IR spectroscopy
-wavenumber which is proportional to frequency as frequency too large
describe the fingerprinting region
-under 1500cm-1
-complicated and contains many signals – picking out functional group difficult
-unique for every compound
which IR range is the functional group identification
-over 1500cm-1
how do computers use IR spectra
-compare the IR spectra against a database of known pure compounds to identify the compound
describe the carbonyl peak
-peak at 1700cm-1
-C=O bond
describe identifying alcohols in an IR spectrum
-broad peak at 2500-3300 cm-1
-data booklet has values for whether this is an alcohol or carboxylic acid
what does the greenhouse effect of a given gas depend on
-it’s atmospheric concentration
-its ability to absorb infrared radiation
-its residence time (time it stays in the atmosphere)
name the greenhouse gases
-carbon dioxide (CO2)
-methane (CH4)
-water vapour (H2O)
what do greenhouse gases do
-they trap the earth’s radiated infra red energy in the atmosphere
describe the order of greenhouse gases
-water is the main greenhouse gas (but is natural)
-followed by carbon dioxide
-and methane
how do the greenhouse gases trap IR
C=O, O–H and C–H bonds
-H2O, CO2 and CH4 absorb IR
why has the concentration of CO2 in the atmosphere increased recently
-due to increasing burning of fossil fuels
how can IR spectroscopy be used in real life
-modern breathalysers measure ethanol in the breath by analysis using infrared spectroscopy
-infrared spectroscopy can be used to monitor gases causing air pollution
describe how a mass spectrometer works
-identifies mr by locating its molecular ion peak
-usually done by electron bombardment where an electron is knocked out of the molecule to form a + molecular ion
-it only detects positive ions
describe fragmentation
-excess energy causes bonds to vibrate and weaken
-so the molecule splits into fragments
-gives a positively charged molecular fragment ion and a neutral molecule
-the fragment ion has a mass and charge so a mass spectrometer can be used to determine mr of fragment
which peak in mass spectrometry identifies the mr of the compound
-the furthest peak along
why does the positive charge on the molecular ion have no affect on identifying the original compound
-it has a +1 charge
-so the removal of an electron does not change its mass
-as mass of an electron is negligible
