carbon 13 nmr

1. CARBON-13 NMR
M.M COLLEGE OF PHARMACY
SUBMITTED BY: PURAV GUPTA[1422710]
SUBMITTED TO:DR. DINESH MEHTA

2. CONTENT
• INTRODUCTION
• PRINCIPLE AND THEORY
• WHY C-13 NMR IS REQUIRED?
• CHARACTERISTICS
• C-13 CHEMICAL SHIFT
• APPLICATIONS

3. INTRODUCTION
• The 13C nucleus is present in only 1.08% natural abundance. Therefore, acquisition of a
spectrum usually takes much longer than in H NMR
• The magnetogyric ratio of the 13C nucleus is about 1/4 that of the ¹H nucleus. Therefore,
the resonance frequency in C NMR is much lower than in ¹H NMR.(75 MHz for 13C as
opposed to 300 MHz for H in a 7.04 Tesla field).
• At these lower frequencies, the excess population of nuclei in the lower spin state is
reduced, which, in turn, reduces the sensitivity of NMR detection.
• Unlike ¹H NMR, the area of a peak is not proportional to the number of carbons giving
rise to the signal. Therefore, integrations are usually not done.
• Each unique carbon in a molecule gives rise to a C-13 NMR signal. Therefore, if there are
fewer signals in the spectrum than carbon atoms in the compound, the molecule must
possess symmetry.
• When running a spectrum, the protons are usually decoupled from their respective
carbons to give a singlet for each carbon atom. This is called a proton-
decoupled spectrum

4. PRINCIPLE & THEORY
• The nuclear magnetic resonance occurs when nuclei aligned with an
applied field are induced to absorb energy and change their spin
orientation with respect to the applied field.
• The energy absorption is a quantized process, and energy absorbed
must equal the energy difference between the two states involved.
𝐸𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑= (E-12𝑠𝑡𝑎𝑡𝑒- E+1/2𝑠𝑡𝑎𝑡𝑒)=hv
• The stronger the applied magnetic field greater the energy difference
between the possible spin states.
∆𝐸 = (𝐵𝑜)

5. • The magnitude of energy level separation also depends on the
particular nucleus involved. Each nucleus has a different ratio of
magnetic moment to angular momentum since each has different
charge and mass.
• This ratio, is called the magnetogyric ratio Υ, is a constant for each
nucleus and determines the energy dependence on the magnetic
field.

7. Why Carbon-13 NMR required?
• Proton NMR used for study of number of nonequivalent proton
present in unknown compound.
• Carbon NMR can used to determine the number of non-equivalent
carbons and to identify the types of carbon atoms(methyl, methylene,
aromatic, carbonyl....) which may present in compound.
• Carbon-13 signals are spread over a much wider range than ¹H signals
making it easier to identify & count individual nuclei.

8. Characteristic feature of C-13 NMR
• The chemical shift of the CMR is wider(8 is 0-240ppm relative to TMS) in
comparison to PMR(8 is 0-14ppm relative to TMS).
• C13-C13 coupling is negligible because of low natural abundance ofC13 in
the compound.
• Spectrum(proton de coupled) each magnetically non equivalent carbon
gives a single sharp peak that does undergo further splitting.
• The area under the peak in CMR spectrum is not necessary to be
proportional to the number of carbon responsible for the signal. Therefore
not necessary to consider the area ratio.
• In proton-coupled spectra, the signal for each carbon or a group of
magnetically equivalent carbon is split by proton bonded directly to that
carbon and the n+1 rule is followed.

9. C-13 CHEMICAL SHIFT
are measured in ppm from the carbons of TMS
• The correlation chart is here divided into sections
1. the saturated carbon atom which appear at Upfield, nearest to
TMS(8-60ppm).
2. Effect of electronegative atom(40-80ppm)
3. Alkenes and aromatic carbon atom(100-170)4) It contain carbonyl
carbon bond. which appear at Downfield value(155-200ppm).

10. CORRELATION CHART

11. INSTRUMENTATION

12. APPLICATION
• CMR is a noninvasive and nondestructive method ,i.e. , especially
used in repetitive In-vivo analysis of the sample without harming the
tissues.
• CMR of biological materials allows for the assessment of the
metabolism of carbon, which is so elementary to life on earth
• CMR, chemical shift range(0-240 ppm) is wider compared to H-
NMR(0-14 ppm), which permits easy separation and identification of
chemically closely related metabolites.
• The low natural abundance of 13C nuclei (1.1%) can be made useof
tagging a specific carbon position by selective.

13. APPLICATION CONT..
• C-13 enrichment, which the signal intensities and helps in tracing the
cellular metabolism.
• C13 nuclei are a stable isotope and hence it is not subjected to
dangers related to radiotracers.
• CMR technique is used for quantification of drug purity to
determination of the composition of high molecular weight
synthetic polymers.