Spectroscopy Flashcards
What 4 major pieces of information is provided by an NMR spectrum
- Number of different nuclear environments- number of peaks (resonances).
- The number of equivalent nuclei in each environment- integration.
- The types of nuclear environments- the position in the spectrum- chemical shift.
- Information on neighbouring environments- spin-spin splitting.
What types of molecules is UV-vis spectroscopy good for
UV-vis causes electrons within a molecule to be promoted to (vacant) higher energy orbitals. Best for extended systems of pi-bonds (chromophores)
What can fragmentation in mass spectrometry be used for
Fragmentation can be used to distinguish isomeric molecules
How can you use mass spectrometry to confirm an empirical formula
The mass spectrometry gives you the mass of a molecule so one worked out empirical formula you can compare to mass spectrometry value to see if you are correct
What is IR spectroscopy used for
To identify or distinguish functional groups
Describe peaks of alcohols and amines
They give large, broad peaks at >3100cm-1
Describe peaks of carbonyls (C=O)
Give intense peaks at around 1700 cm-1
What can you use IR to distinguish
Different types of carbonyl groups as different carbonyl groups have different stretching frequencies
What does elemental analysis give you
The mass fractions of C, H, N and other atoms (X) of a sample
How do you use elemental analysis to work out an empirical formula
- Sum the fractions given, minus sum to give % of oxygen.
- Divide mass % by Ar to give molar %.
- Divide all by smallest number to give amount of each element present.
How do you use empirical formula to work out molecular formula
- Calculate DBE of empirical formula to check if is molecular formula
- If not valid DBE then multiply empirical formula until get valid DBE
