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Module 5 - Chapter 29 - Chromatography and spectroscopy II - Coggle Diagram
Module 5 - Chapter 29 - Chromatography and spectroscopy II
Carbon 13 NMR
Information
Number of different carbon environments - number of peaks
Types of carbon enviroment present - from chemical shift
Types of carbon enviroments
C-C
C-(O,N,Cl,Br
Highly electronegative atoms pull electrons in the bond away from the carbon
Carbon is more deshielded
More energy is required to reach resonant state, nuclei have a greater chemical shift
C=C
Electrons in pi bons spin due to magnetic field and this generates a secondary magnetic field
Carbon nuclei are exposed to a greater magnetic field
Nuclei is more shielded so more energy is required to reach resonant state
C=O
Deshielded by electronegative atom and stronger magnetic field from the pi bons
Greater chemical shift
Chemical environment
Carbon atoms bonded to different atoms or groups will absorb at different chemical shifts
Two carbons positioned symmetrically in a molecules have same chemical enviroment and contribute to the same peak
Proton NMR
Information
Number of proton environments
Types of proton environments present
Relative numbers of each type of proton - from integration traces or ratio numbers of relative peak areas
Number of non-equivalent protons adjacent to a given proton
Equivalent/non equivalent
Equivalent protons absorb at same chemical shift - increases size of the peak
Protons of different types have different chemical environments and are non-equivalent
Relative numbers of each type of proton
Ratio of areas under each peak gives the ratio of number of protons responsible for each peak
NMR spectrometer measured the area under each peak as an integration trace
Integration trace is shows as an extra line on the spectrum or as anumber of the relative peak area
Spin-spin coupling
Proton NMR peak can be split into sub peaks caused by protons spin interacting with the spin states of nearby protons that are in different enviroments
This provides info about the number of protons bonded to adjacent carbon atoms
n + 1 rule
Number of sub peaks is one greater than the number of adjacent protons causing the splititng
a proton with n protons attached to an adjacent carbon atom, the number of sub-peaks in a splitting pattern = n +1
Only occurs if adjacent protons are in different environment from the protons being split
In pairs
If you see one splitting pattern, there must always be another - each proton splits the signal of the other
Hydroxyl and amino protons
NH and OH protons may be involved in hydrogen bonding and the NMR peaks are often broad and of variable chemical shift
OH and NH peaks can occur at almost any chemical shift
Proton exchange
1) Proton NMR spectrum is run as normal
Small volume of D2O is added to mixture and second spectrum is run
Deuterum exchanges and replaces OH and NH protons in sample with deuterium atoms
This causes peak responsible for OH and NH to disappear
Any protons bonded to electronegative atoms hydrogen bond with D2O, this weakesn O-H/ N-H bond