information content available through nmr
TRANSCRIPT
![Page 1: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/1.jpg)
Information Content Available
Through NMR
![Page 2: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/2.jpg)
We need to measure the NMR signals…
![Page 3: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/3.jpg)
Tetramethylsilane (TMS) is our reference for 1H, 13C and 29Si.The chemical shift (denoted δ)
varies in different chemical environments.
δ = [ (νobs – νTMS ) / νTMS ] x 106
![Page 4: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/4.jpg)
Chemical shifts depend on the electronegativities of nearby
atoms
![Page 5: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/5.jpg)
Having 2n+2 π electrons in a ring allows for charge circulation
Image courtesy of the U.S. Geological Survey
![Page 6: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/6.jpg)
![Page 7: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/7.jpg)
We also want to know how much of each signal we have
![Page 8: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/8.jpg)
NMR provides information on the relative amounts of
chemically distinct molecular sites (integrals and intensities)
![Page 9: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/9.jpg)
Quantitation requires…
• Waiting five times the longest spin-lattice relaxation time T1
Mz(t) = M0 [1 - exp (-t / T1)]
• The absence of any enhancement, such as that arising from decoupling
η = γX / (2 γA)
![Page 10: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/10.jpg)
1H 1-D integration
![Page 11: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/11.jpg)
13C spectra provide useful intensity information
![Page 12: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/12.jpg)
How do spins talk to each other?
Image courtesy of U.S. Air Force
![Page 13: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/13.jpg)
Through-bond connectivity is revealed
through J-couplings
![Page 14: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/14.jpg)
The magnitude of J1J’s (ca. 125-160 Hz for 1H-13C, sometimes
more, used in HMQC, HSQC, and INADEQUATE)
• 2J’s (geminal couplings, 2-15 Hz) • 3J’s (vicinal couplings, 0-15 Hz) , • sometimes 4J’s (0-4 Hz)• and even 5J’s (0-2 Hz)
![Page 15: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/15.jpg)
Geometry controlling magnitude of 2J’s and 3J’s is well
understood and expressed through the Karplus relationship
![Page 16: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/16.jpg)
2J Karplus relationship
![Page 17: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/17.jpg)
3J Karplus relationship
![Page 18: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/18.jpg)
Measurable 4J’s are found in rigid molecules
![Page 19: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/19.jpg)
1H-1H gCOSY
(gradient COrrelation
SpectroscopY)
![Page 20: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/20.jpg)
1H-13C HMQC and HSQC(Heteronuclear Multiple Quantum Correlation &
Heteronuclear Single Quantum Correlation)
![Page 21: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/21.jpg)
1H-13C gHMBC
![Page 22: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/22.jpg)
Other important through-bond experiments:
1H-1H DQFCOSY(Double Quantum Filtered COrrelation SpectroscopY)
and13C-13C INADEQUATE
(Incredible Natural Abundance DEtection blah blah blah)
![Page 23: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/23.jpg)
We can also detect interactions…
THROUGH SPACE
![Page 24: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/24.jpg)
Through-space effects: the dipolar interaction gives us the
nuclear Overhauser effect (NOE)
![Page 25: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/25.jpg)
Consider a 1H-13C spin pair at equilibrium
![Page 26: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/26.jpg)
Now we irradiate (decouple) the 1H transitions
![Page 27: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/27.jpg)
The double quantum transition relaxes the fastest (sometimes)
![Page 28: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/28.jpg)
1H-1H NOESY(Nuclear Overhauser Effect SpectroscopY)
![Page 29: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/29.jpg)
Those are the basic tools from which we choose
(Photo courtesy of JM, http://www.logodesignweb.com/stockphoto)
![Page 30: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/30.jpg)
We start with assigning a molecule of known structure: ethyl nipecotate
![Page 31: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/31.jpg)
Entry points
• Ethyl group• Carbonyl carbon• Methylenes α to N• Lone methine @ 3
![Page 32: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/32.jpg)
In simple problems:Following the identification of entry points, we use 3JHH’s to assign 1H’s adjacent to those we already know using the
gCOSY
![Page 33: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/33.jpg)
In complex problems:Following the identification of
entry points, we use 3-5JHH’s and 2-5JHC’s to assign spins
![Page 34: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/34.jpg)
1H 1-D
![Page 35: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/35.jpg)
13C 1-D
![Page 36: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/36.jpg)
1H-13C HMQC
![Page 37: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/37.jpg)
1H-1H gCOSY
![Page 38: Information Content Available Through NMR](https://reader031.vdocument.in/reader031/viewer/2022022121/6212ba26321d7652485e66c8/html5/thumbnails/38.jpg)
For six-membered rings, we normally assume a chair
conformation, and so the dihedrals are either trans or gauche