Download - Carbon 13
![Page 1: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/1.jpg)
Carbon-13Nuclear
Magnetic Resonance
Spectroscopy
![Page 2: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/2.jpg)
Presented By:Arif Iqbal
Shahid Roll No.:
108
![Page 3: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/3.jpg)
Introduction
Nuclear Magnetic Resonance concern the magnetic properties of certain atomic nuclei. It concern the atoms having Spin Quantum Number ( I ).
1
![Page 4: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/4.jpg)
IntroductionSome atoms have no spin. Atoms having even atomic number and mass number (12C, 16O).Some other nuclei have spin. Atoms having either odd atomic number or mass number or both (1H,13C,19F).
2
![Page 5: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/5.jpg)
Carbon-13 NMR12C have no Magnetic
Spin and produces no NMR signal.13C have Magnetic Spin I= ½13C accounts for only 1.1% of naturally occurring carbon
3
![Page 6: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/6.jpg)
Carbon-13 NMRThe low probability of
adjacent 13C atoms leads to no detectable carbon-carbon splitting No coupling between 13C and C. 13C have weak signal13C have strong coupling with H 13C have weak coupling with C
4
![Page 7: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/7.jpg)
13C NMR Spectroscopy: Signal Averaging and FT-
NMRTwo techniques have been developed to detect the 13C isotope in an organic sample by NMR:
Signal averaging (increases instrument sensitivity)
Fourier-transform NMR (increases instrument speed)
5
![Page 8: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/8.jpg)
Signal averaging
increases instrument sensitivity. Any individual 13C NMR spectrum is extremely “noisy”, but when hundreds of individual runs are added together by computer and then averaged, a greatly improved spectrum results.
6
![Page 9: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/9.jpg)
Signal averaging
7
![Page 10: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/10.jpg)
Fourier-transform NMRincreases instrument speed.
In the FT-NMR technique, all signals are recorded simultaneously.All 1H and 13C in the sample resonate at once, and the complex composite signal is manipulated using so-called Fourier transforms before it can be displayed. 8
![Page 11: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/11.jpg)
Fourier-transform NMR
9
![Page 12: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/12.jpg)
Fourier-transform NMR
The sensitivity of 13C is only 1/5700 of 1H; This sensitivity problem is overcome with Fourier Transform (FT) NMR instrumentation
10
![Page 13: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/13.jpg)
Spin-Spin SplittingIt is unlikely that a 13C would be adjacent to another 13C, so splitting by carbon is negligible.13C will magnetically couple with attached protons and adjacent protons.These complex splitting patterns are difficult to interpret.
11
![Page 14: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/14.jpg)
Recording of CMR Spectra
The CMR Spectra is recorded in decoupling condition.The nuclei are decoupled by double irradiation
12
![Page 15: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/15.jpg)
Spin DecouplingTwo Types of decoupling:
Homonuclear decoupling:Decoupling
of same nuclei (C and C) or (H and H).
Heteronuclear decoupling:Decoupling
of different nuclei C and H.Broad Band DecouplingOff resonance decoupling
13
![Page 16: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/16.jpg)
Broad Band Decoupling: A sample is irradiated with two different radio
frequencies.One to excite all 13C nuclei.A second broad spectrum of frequencies to
cause all hydrogen in the molecule to undergo rapid transitions between their nuclear spin states.
On the time scale of a 13C-NMR spectrum, each hydrogen is in an average or effectively constant nuclear spin state, with the result that 1H-13C spin-spin interactions are not observed; they are decoupled.
Thus, each different kind of carbon gives a single, unsplit peak. 14
![Page 17: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/17.jpg)
Off resonance decoupling
The Coupling can be achieved by off setting the high power proton decoupler by about 1000-2000 Hz up field or about 2000-3000 Hz downfield from the frequency of TMS without using the noise generator.
Groups signals- CH3 quartets- CH2 - triplets
Doublets
A quarternary Carbon Singlet
C H
15
![Page 18: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/18.jpg)
Proton off-resonance decoupling
Broad band decoupling16
![Page 19: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/19.jpg)
Interpreting 13C NMRThe number of different signals indicates the number of different kinds of carbon.The location (chemical shift) indicates the type of functional group.The peak area indicates the numbers of carbons (if integrated).
17
![Page 20: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/20.jpg)
Interpreting 13C NMR
18
![Page 21: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/21.jpg)
Chemical Shift in CMR Spectra
C-13 NMR has d 0 to 220 ppm (1HNMR d 0 to 12 ppm)CMR spectra is recorded under proton decoupling conditionIn the CMR multiplets, no need to determine area ratios.
19
![Page 22: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/22.jpg)
13C Chemical shifts are most affected by:
Hybridization of 13C atom: –sp3 C signal is in the range 0-90
–sp2 C signal is in the range 110-220
–C=O signal is at the low-field end, in the range 160-220
20
![Page 23: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/23.jpg)
13C Chemical shifts are most affected by:
Characteristic Carbon NMR Chemical Shifts (ppm)
(CH3)4Si = TMS = 0.00 ppm (singlet) CDCl3 (solvent) = 77.0 ppm (triplet)
RCH3 0 – 40 RCH2Cl 35 – 80 benzene ring 110 – 160
RCH2R 15 – 55 R3COH 40 – 80 C=O ester 160 – 180
R3CH 20 – 60 R3COR 40 - 80 C=O amide 165 – 180
RCH2I 0 – 40 RCCR 65 – 85 C=O carboxylic acid 175 – 185
RCH2Br 25 - 65 R2C=CR2 100 - 150 C=O aldehyde, ketone 180 – 210
21
![Page 24: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/24.jpg)
Interpreting 13C NMR
22
![Page 25: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/25.jpg)
13C Chemical shifts are most affected by:
Electro negativity of nearby atoms:
C bonded to O, N, or halogen absorb downfield because O, N, or halogen pull electrons away from nearby 13C atoms, decreasing their electron density and “deshielding” them. 23
![Page 26: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/26.jpg)
24
![Page 27: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/27.jpg)
Example
25
![Page 28: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/28.jpg)
Example
200 180 160 140 120 100 80 60 40 20 0
H
H
H H
CCH2CH2CH2CH3
HOCH
CH
CH
CC
OCH3CH2
CH2CH2
26
![Page 29: Carbon 13](https://reader035.vdocument.in/reader035/viewer/2022062319/55862933d8b42ac54a8b4976/html5/thumbnails/29.jpg)
Thank You