spectroscopy
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molecular ion peak
peak on spectrum formed when molecule looses an electron forming a positive ion and an electron - on far right of spectrum (small M+1 peak after it)
what does molecular ion peak tell us?
the Mr of the compound
fragment ions
when molecular ion is broken down through fragmentation producing fragment ion + RADICAL
products of fragmentation
positive ion uncharged radical - UNDETECTED
how does IR spectroscopy work?
• atoms are joined by covalent bonds which contain energy and vibrate (increase as temp increase) • bond absorbs radiation at same frequency as bond • increases its vibrations
2 types of movement by covalent bonds
stretch bend
how does global warming link to IR radiation
• most of suns radiation doesn’t disturb atmospheric gases • some radiation re-emitted from earth and is longer wavelength IR radiation • absorbed in bonds In CO2, water vapour and methane • causing bonds to vibrate more and re-emit this energy as radiation which increases atmospheric temp close to the earths surface = global warming
fingerprint region
below 1500cm-1
use of fingerprint region
identify specific molecules as region is unique to each compound
O-H (alcohol) wavenumber
3200-3600
C-H wavenumber
2850-3100
C=O wavenumber
1630-1820
O-H (carb. acid) wavenumber
2500-3300 broad
applications of IR spectroscopy
• pollutants can be identified using IR fingerprint region - remote sensors used to analyse IR spectra of vehicle emissions to monitor local pollution • breathalysers - pass beam of IR radiation through breath to detect ethanol
order of use of analysis for unknown compound
1) elemental - find empirical formula 2) mass spec - find molecular mass from molecular ion peak - fragment ions identify different sections of molecule 3) IR spec. - identify bonds and functional groups
what does NMR use (2)
• magnetic frequency - radio frequency radiation
how does NMR work
(odd number) of nuclei spin - has 2 different spin states, in right conditions (high frequency radiation and strong magnetic field) nucleus rapidly flips between 2 states = RESONANCE
typical NMR radiowave frequencies
100, 200 or 400 MHz
chemical shift - units
difference in radio frequencies absorbed by nuclei in molecule being analysed and same nuclei in TMS - ppm
why deuteriated solvents?
doesn’t contain H1 - therefore won’t have signal on spectrum for NMR
typical deuterated solvent
CDCl3
what does C13 NMR tell us (2) - from what?
• number of C environments (number of peaks) - types of C environments (chemical shift)
what does proton NMR tell us (4) - from what?
• number of H environments (number of peaks) • type of environment (chemical shifts) • relative number of H in each environment (relative area of signals) • number of Hs on adjacent carbons (splitting patterns)
what causes splitting? - what does it tell us?
H atoms on adjacent carbons N+1 rule