13C NMR SPECTRUM OF TOLUENE and OTHERS

C 13 NMR SPECTRUM OF TOLUENE
OTHERS ARE SELF EXPLANATORY

SPECTRUM 2




SPECTRUM 3

 
SPECTRUM 4

 
SPECTRUM5
 
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SPECTROSCOPY BASICS

 SPECTROSCOPY BASICS
AT

http://www.chemistry.ccsu.edu/glagovich/teaching/316/index.html

IR spectroscopy detects that oxygen defects act as active centres

oxygen defects act as active centres

In the chemical industry, heterogeneous catalysis is vital for the manufacture of basic or fine chemicals, in catalytic converters of exhaust gas and for the chemical storage of solar energy. A new infrared spectroscopy method can study processes at surfaces of oxides used as catalysts.
In the chemical industry, heterogeneous catalysis is vital for the manufacture of basic or fine chemicals, in catalytic converters of exhaust gas and for the chemical storage of solar energy. Scientists from the Karlsruhe Institute of Technology (KIT) and Ruhr-Universität Bochum (RUB) in Germany have developed a new infrared spectroscopy method in order to study processes at surfaces of oxides used as catalysts; their results have been published in Angewandte Chemie (doi: 10.1002/ange.201200585).

http://www.spectroscopyeurope.com/news/research/3106-ir-spectroscopy-detects-that-oxygen-defects-act-as-active-centres

Simple method for identifying incorrect structures of organic molecules due to NMR misassignments

An end to chasing molecules that were never there?
	Simple method for identifying incorrect structures of organic molecules due to NMR misassignments http://www.rsc.org/chemistryworld/2013/06/nmr-misassignments-spreadsheet-artificial-neural-networks

ORGANIC SPECTROSCOPY SOLVED PROBLEM-CAMPHOR

SOLVED PROBLEM-CAMPHOR

CAMPHOR, 

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1 H NMR BASICS

1 H NMR BASICS

Hydrogen NMR There are three isotopes of hydrogen used in NMR spectroscopy:  1Hydrogen, 2Deuterium and 3Tritium. Each isotope resonates at a  very different frequency for example  if 1H resonates at 400 MHz then 2H resonates at 61.402 MHz.  Only one isotope is observed at a time  because the spectrometer transmits and receives over a very limited frequency range.  The chemical shift ranges for all three nuclei are virtually identical  and can be used for preliminary analysis but there the similarity ends. 3Tritium is not commonly measured by NMR because it is radioactive. Each type of signal has a characteristic chemical shift range (fig. 1)  that can be used for initial assignment. Fig. 1. Chemical shift ranges of protons  according to their chemical environment Choose the structure that most closely represents the hydrogen in question.  R = alkyl or H, Ar = aryl. 1Hydrogen (Proton) NMR The 1D 1H (Proton) NMR experiment is the most common NMR experiment. The proton (1Hydrogen nucleus) is the most sensitive nucleus apart from tritium) and usually yields sharp signals. Even though its chemical  shift range is narrow, its sharp signals make proton NMR very useful. A typical analysis of a 1H NMR spectrum may proceed as follows: The number of protons of each type in the spectrum of a pure sample can be obtained directly from the integrals of each multiplet. This is only true if the multiplets are well separated and do not overlap the solvent or residual water signals and provided that the molecule is not undergoing slow conformational exchange. A routine NMR spectrum yields integrals with an accuracy of +/-10%.  Accuracies of +/-1% can be achieved by increasing the relaxation delay  to five times the longitudinal relaxation time (T1) of the signals of interest. Where multiplets overlap, the total integral of the spectral region may be used. From the table of the proton chemical shifts one obtains information about  each type of proton and can carry out a preliminary assignment. Consider ethanol as an example (Fig. 2). Using chemical shifts, the peak at 1.2 ppm is in the expected range for CH3 (methyl) and at 3.7 and 3.9 ppm are compatible with CH2 (methylene). The chemical shift of OH is very dependent on solvent and other experimental conditions so cannot be assigned by chemical shift alone. Using integration, we expect CH3 to have an integral of three, CH2 to have an integral of two and OH to have an integral of one. This is the case and so the assignment is complete. Fig. 2. 1H NMR spectrum of ethanol in CDCl3 For other molecules this is not sufficient and the multiplet structure is needed to complete the assignment. The multiplets (fig. 3) arise from spin-spin couplings that are transmitted through chemical bonds and yield information  about the immediate molecular environment.  In the case of CH3 and OH, they are split by the two neighboring protons of the CH2  to yield a triplet pattern called AX2. (Click here to see a list of common  homonuclear splitting patterns and a description of heteronuclear coupling.) The CH2 is split by the single OH proton and the three CH3 protons to form the AX3Y pattern.  Fig. 3. Multiplet structures from the 1H NMR spectrum of ethanol in CDCl3   Having determined the multiplicity, one may measure the coupling constants.  These are measured in Hz (not ppm), as they are field independent. If you find that two (and only two) multiplets contain the same coupling constant then  you know that they arise from nearby protons. The coupling constant gives an indication of the distance between the protons. In general 10 to 18 Hz means two bond or three bond trans to a C=C double bond. Coupling constants between 1 to 10 Hz  indicate three-bonds or more bonds if delocalized. Less than 1 Hz usually means four or more bonds. In addition to homonuclear couplings, the multiplets may be split by other nuclei such as 19Fluorine or 31Phosphorus. (If suchheteronuclear couplings are undesirable they may be decoupled. The best pulse sequence in such a case is that for inverse gated decoupling.) Properties of 1H Property Value Spin ½ Natural abundance 99.9845% Chemical shift range 13 ppm, from -1 to 12 Frequency ratio (Ξ) 100.000000% Reference compound TMS < 1% in CDCl3 = 0 ppm Linewidth of reference 0.08 Hz T1 of reference 14 s Receptivity rel. to 1H at natural abundance 1.000 Receptivity rel. to 1H when enriched 1.000 Receptivity rel. to 13C at natural abundance 5870 Receptivity rel. to 13C when enriched 5871 2Deuterium NMR 2Deuterium (heavy hydrogen) NMR is usually used for field frequency lock. At natural abundance it has very low sensitivity but when enriched it is of  medium sensitivity. Deuterium usually yields broad signals whose line width typically varies between a few hertz and a few kilohertz.  The spectrum has the same narrow chemical shift range as for   1H but its low resolution and lower sensitivity make it a poor alternative. Deuterium-deuterium couplings are about 40 times smaller that proton-proton couplings and are therefore not observed.  However, in partially deuterated molecules small proton-deuterium couplings can be obseved. The main use of deuterium spectra is for determining the effectiveness of chemical deuteration (fig. 4). Fig. 4. 1H and 2H NMR spectra of  Amphetamine sulfate–d3 showing successful specific deuteration of the methyl Properties of 2H Property Value Spin 1 Natural abundance 0.0155% Chemical shift range 13 ppm, from -1 to 12 Frequency ratio (Ξ) 15.350609% Reference compound TMS-d12 neat = 0 ppm Linewidth of reference 1.7 Hz T1 of reference 1 s Receptivity rel. to 1H at natural abundance 1.50 × 10-6 Receptivity rel. to 1H when enriched 9.65 × 10-3 Receptivity rel. to 13C at natural abundance 8.78 × 10-3 Receptivity rel. to 13C when enriched 56.7 Linewidth parameter 0.41 fm4 3Tritium NMR 3T is the only nucleus more sensitive than proton (1H). Being a spin-½ isotope of hydrogen, spectra of fully tritiated compounds  look similar to 1H with effectively the same chemical shifts  but with slightly higher sensitivity, dispersion and coupling constants. However,   3T is very radioactive so most NMR studies are carried out with partially and specifically labeled compounds. Properties of 3H Property Value Spin ½ Natural abundance 0.0000000000000003% Chemical shift range 13 ppm, from -1 to 12 Frequency ratio (Ξ) 106.663974% Reference compound TMS-t1 <1% in CDCl3 = 0 ppm Linewidth of reference ~0.1 Hz T1 of reference ~20 s Receptivity rel. to 1H at natural abundance 4 × 10-18 Receptivity rel. to 1H when enriched 1.21 Receptivity rel. to 13C at natural abundance 2 × 10-14 Receptivity rel. to 13C when enriched 7103

Carbon-13 NMR

Carbon-13 NMR (¹³C NMR or sometimes simply referred to as carbon NMR) is the application of nuclear magnetic resonance (NMR) spectroscopy to carbon. It is analogous to proton NMR (1H NMR) and allows the identification of carbon atoms in an organic moleculejust as proton NMR identifies hydrogen atoms. As such ¹³C NMR is an important tool in chemical structure elucidation in organic chemistry. ¹³C NMR detects only the 13C isotope of carbon, whose natural abundance is only 1.1%, because the main carbon isotope,12C, is not detectable by NMR since it has zero net spin.

Implementation

¹³C NMR has a number of complications that are not encountered in proton NMR. ¹³C NMR is much less sensitive to carbon than ¹H NMR is to hydrogen since the major isotope of carbon, the ¹²C isotope, has a spin quantum number of zero and so is not magnetically active and therefore not detectable by NMR. Only the much less common ¹³C isotope, present naturally at 1.1% natural abundance, is magnetically active with a spin quantum number of 1/2 (like ¹H) and therefore detectable by NMR. Therefore, only the few ¹³C nuclei present resonate in the magnetic field, although this can be overcome by isotopic enrichment of e.g. protein samples. In addition, thegyromagnetic ratio (6.728284 10⁷ rad T⁻¹ s⁻¹) is only 1/4 that of ¹H, further reducing the sensitivity. The overall receptivity of ¹³C is about 4 orders of magnitude lower than ¹H.

^[1]

Another potential complication results from the presence of large one bond J-coupling constants between carbon and hydrogen (typically from 100 to 250 Hz). In order to suppress these couplings, which would otherwise complicate the spectra and further reduce sensitivity, carbon NMR spectra are proton decoupled to remove the signal splitting. Couplings between carbons can be ignored due to the low natural abundance of ¹³C. Hence in contrast to typical proton NMR spectra which show multiplets for each proton position, carbon NMR spectra show a single peak for each chemically non-equivalent carbon atom.

In further contrast to ¹H NMR, the intensities of the signals are not normally proportional to the number of equivalent ¹³C atoms and are instead strongly dependent on the number of surrounding spins (typically ¹H). Spectra can be made more quantitative if necessary by allowing sufficient time for the nuclei to relax between repeat scans.

High field magnets with internal bores capable of accepting larger sample tubes (typically 10 mm in diameter for ¹³C NMR versus 5 mm for ¹H NMR), the use of relaxation reagents,^[2] for example Cr(acac)₃ (chromium (III) acetylacetonate, CAS number 21679-31-2), and appropriate pulse sequences have reduced the time needed to acquire quantitative spectra and have made quantitative carbon-13 NMR a commonly used technique in many industrial labs. Applications range from quantification of drug purity to determination of the composition of high molecular weight synthetic polymers.

¹³C chemical shifts follow the same principles as those of ¹H, although the typical range of chemical shifts is much larger than for ¹H (by a factor of about 20). The chemical shift reference standard for ¹³C is the carbons in tetramethylsilane (TMS), whose chemical shift is considered to be 0.0 ppm.

Typical chemical shifts in ¹³C-NMR

DEPT spectra

DEPT spectra of propyl benzoate

DEPT stands for Distortionless Enhancement by Polarization Transfer. It is a very useful method for determining the presence of primary, secondary andtertiary carbon atoms. The DEPT experiment differentiates between CH, CH₂and CH₃ groups by variation of the selection angle parameter (the tip angle of the final ¹H pulse):

• 135° angle gives all CH and CH₃ in a phase opposite to CH₂
• 90° angle gives only CH groups, the others being suppressed
• 45° angle gives all carbons with attached protons (regardless of number) in phase

Signals from quaternary carbons and other carbons with no attached protons are always absent (due to the lack of attached protons).

The polarization transfer from ¹H to ¹³C has the secondary advantage of increasing the sensitivity over the normal ¹³C spectrum (which has a modest enhancement from the NOE (Nuclear Overhauser Effect) due to the ¹H decoupling).

APT spectra 

Another useful way of determining how many protons a carbon in a molecule is bonded to is to use an Attached Proton Test, which distinguishes between carbon atoms with even or odd number of attached hydrogens. A proper spin-echo sequence is able to distinguish between S, I₂S and I₁S, I₃S spin systems: the first will appear as positive peaks in the spectrum, while the latter as negative peaks (pointing downwards), while retaining relative simplicity in the spectrum since it is still broadband proton decoupled.

Even though this technique does not distinguish fully between CH_n groups, it is so easy and reliable that it is frequently employed as a first attempt to assign peaks in the spectrum and elucidate the structure.^[3]

1. ^ R. M. Silverstein, G. C. Bassler and T. C. Morrill (1991). Spectrometric Identification of Organic Compounds. Wiley.
2. ^ Caytan, Elsa; Remaud, Gerald S.; Tenailleau, Eve; Akoka, Serge, GS; Tenailleau, E; Akoka, S (2007). "Precise and accurate quantitative 13C NMR with reduced experimental time". Talanta 71 (3): 1016–1021. doi:10.1016/j.talanta.2006.05.075. PMID 19071407
3. ^ Keeler, James (2010). Understanding NMR Spectroscopy (2nd ed.). John Wiley & Sons. p. 457. ISBN 978-0-470-74608-0.

• Carbon NMR spectra, where there are three spectra of ethyl phthalate, ethyl ester of orthophthalic acid: completely coupled, completely decoupled and off-resonance decoupled (in this order).

• For an extended tabulation of ¹³C shifts and coupling constants.