Z Score,T Score, Percential Rank and Box Plot Graph
Proton nmr spectroscopy present
1. Introduction to NMR Spectroscopy
• Nuclear magnetic resonance spectroscopy is a powerful analytical technique
used to characterize organic molecules by identifying carbon-hydrogen
frameworks within molecules.
• Two common types of NMR spectroscopy are used to characterize organic
structure: 1H NMR is used to determine the type and number of H atoms in a
molecule; 13C NMR is used to determine the type of carbon atoms in the
molecule.
• The source of energy in NMR is radio waves which have long wavelengths, and
thus low energy and frequency.
• When low-energy radio waves interact with a molecule, they can change the
nuclear spins of some elements, including 1H and 13C.
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21. A proton n.m.r. spectrum can give us a lot of useful information about a molecule.
22. It can tell us how many different chemical environments there are in the
molecule. Hydrogen atoms in different environments are non-equivalent.
23. It can’t tell us how many hydrogen atoms the molecule contains, but it can tell us
the ratio of the number of hydrogen atoms in each chemical environment.
24. It can give us information about the nature of the different chemical environments.
25. It can also give us information about adjacent non-equivalent hydrogen atoms in
different chemical environments.
26. This is the displayed formula for ethanol. How many different chemical
environments does it have?
27. There are three equivalent hydrogen atoms in this chemical environment.
28. There are two equivalent hydrogen atoms in this chemical environment.
29. There is just one hydrogen atom in this chemical environment.
30. What peaks would we expect in a low-resolution n.m.r. spectrum of ethanol?
31. The CH 3 group contains three hydrogen atoms, which form a large peak
32. The CH 2 group contains two hydrogen atoms, which form a smaller peak.
33. The OH group contains one hydrogen atom, which forms a small peak.
34. The OH group contains one hydrogen atom, which forms a small peak.
35. The position of each peak on the n.m.r. spectrum gives us information about the
corresponding chemical environment.
36. The hydrogen atom in the OH group is attached to an oxygen atom, which is very
electronegative. A hydrogen atom like this is deshielded.
37. The peak it produces is shifted downfield in the spectrum.
38. The hydrogen atoms in the CH 3 group are far from the oxygen atom. They are
shielded.
39. The peak they produce is upfield in the spectrum, close to 0 ppm.
40. Chemical shifts are measured relative to the peak produced by a standard
substance, called TMS. By definition, δ is 0 for TMS.
41. This is TMS, tetramethylsilane. Why is it chosen for the reference peak?
62. Both methyl groups are in the same chemical environment. Their hydrogen atoms
are all equivalent and will produce a single peak in the n.m.r. spectrum.
68. Some of the peaks are split into clusters of smaller peaks in high-resolution
proton n.m.r. spectra, because of spin-spin coupling.
69. This happens if non-equivalent hydrogen atoms are adjacent to each other. No
splitting occurs otherwise.
70. Without spin-spin coupling a single peak forms, called a singlet, just as in a low-
resolution spectrum.
71. If hydrogen atoms in one chemical environment are adjacent to one hydrogen atom
in another chemical environment, the peak they produce will split into two.
72. This is called a doublet, with a ratio of peak areas of 1:1.
73. If hydrogen atoms in one chemical environment are adjacent to two hydrogen
atoms in another chemical environment, the peak they produce will split into three.
74. This is called a triplet, with a ratio of peak areas of 1:2:1.
75. If hydrogen atoms in one chemical environment are adjacent to three hydrogen
atoms in another chemical environment, the peak they produce will split into four.
76. This is called a quartet, with a ratio of peak areas of 1:3:3:1.