43 0 obj <>/Filter/FlateDecode/ID[<77D62677FBA02219104EA17F4BD765AE><6190252755028442878B058C1D8B69EA>]/Index[7 123]/Info 6 0 R/Length 145/Prev 59968/Root 8 0 R/Size 130/Type/XRef/W[1 2 1]>>stream You must be prepared to find small discrepancies of this sort in more complicated molecules - but don't worry about this for exam purposes at this level. Most 13C NMR spectra that you are going to see are decoupled. Naphthenic CH.

Which one produced the C-13 NMR spectrum below?

You can pick out all the peaks in this compound using the simplified table above. * Referenced to TMS (tetramethylsilane) at 0 ppm (units = ppm). 1-methylethyl propanoate is also known as isopropyl propanoate or isopropyl propionate.

A table of typical chemical shifts in C-13 NMR spectra.

@���$��Z��p�����5@"pK 2@Ps�$ K�à�JT��^� ��$p�x�@=Ai��@�xPl�J� Y`Wy�h�q �@����x2�L��������|vp���-��˼䊷\�"[��g�a��z�&��z�/��\�S,תO��A�(�e�'�켸-�g_���O1Hݮ�ҳ^W�R�ZF��e�=�2(*+���B��Dp�V��J�k�L�J�o%��j6ッo��������_r�wL������l��o�C�5�V���R��͠��W�������t��I1��C��z����O�Mn���e��I���全7@�Z$ (2) Schematic diagrams of NMR chemical shift data for 13C Like the proton NMR diagrams, the figure and the table show similar information presented in different ways and both have their merits. What if you needed to work it out? (Looking at the more detailed table, this peak is due to the carbon in a carbon-oxygen double bond in an acid or ester.). “extra peaks” in a variety of commonly used NMR solvents, in the hope that this will be of assistance to the practicing chemist. ���� ! " Notice that they aren't in exactly the same environment, and so don't have the same shift values. Below is a representative 13 C spectrum and a table of most important chemical shifts in 13 C NMR: Among the carbonyls, aldehydes and ketones are in the most downfield region (past 200 ppm) since, unlike carboxylic acids, esters, amides and others, they don’t have a heteroatom which is in resonance with the carbonyl group thus reducing the partial positive charge of the C=O carbon. 3J coupling: the Karplus equations and correlation curve The relationship between the dihedral angle and the vicinal coupling constant 3J (as observed from 1H NMR spectra) is given theoretically by the Karplus equations: 3J ab = J 0 cos2Θ – 0.28 (for 0˚ < Θ < 90˚ range) 3J ab = J 180 cos2Θ – 0.28 (for 90˚ < Θ < 180˚ range) H H Θ Peak Position* Assignment 11.0 – 12.5 CH3 gamma or further from aromatic ring. �tH�����TB�h��B9�3B�8L,�cfR�S��-0?��K�1�'L]����^LK

Again, you can't read any reliable information directly from peak heights in these spectra. In propanone, the two carbons in the methyl groups are in exactly the same environment, and so will produce only a single peak. 7 0 obj <> endobj Discussions are given for the case of acyclic alkanes; the replacement of a proton by any substituent in cyclic alkanes gives rise to changes of the chemical shifts, particularly at the carbon bearing the substituent. 7�~�����asڬ�r�3�j�Է��;Ū�PtN��A���ʛ0(��� :�������p!$%��x�J!XX?���&�~ In A and B, there are four totally different environments. [�BN i�y�D�Z�#�i����;�� �t%h�"9~Pã�?��WYh�AY���n>���Xs��~��F����

That would be consistent with C-C-O in the structure. endstream endobj startxref However, you need to know that signal splitting in 13C NMR by neighboring hydrogens does occur which leads to complicated splitting patterns. The peak at 174 is due to a carbon in a carbon-oxygen double bond. Right next to the carbonyl region, you have the unsaturated region (100-160 ppm), and this includes alkenes, aromatic and other groups with π bonds.

That means that the peak at about 60 (the larger chemical shift) is due to the CH2 group because it has a more electronegative atom attached. �{,�M! NMR Frequency Tables Isotope Be Spin 7.59 Nat. The compound is ethoxyethane (diethyl ether), CH3CH2OCH2CH3. 129 0 obj <>stream It is the bottom value given in the detailed table. And the methyl group on the end has exactly the sort of value you would expect for one attached to C=O. The approximations are perfectly good, and we will work from this table: There is a peak for carbon(s) in a carbon-oxygen single bond and one for carbon(s) in a carbon-carbon single bond.

.�/ ya*��`4 /��"qu2�aω&r� d�**�gc$�B(�/Xi�PL��9�3��AB��uK ��hX�(�W���+����lz�'/Vy^E"�m��F�����y�Tbj9��>b�@����4b�@�H���EPϡ�4v�P��}P����L��O�E5�H'�"�b:7]�������4$L��Lߟ�Y�Q���Y`�ºA �Ђ�I��hA8$�uK�Ï�2�e١��PCj4@!c~�}��&�Qf�i�43�V�E��!�z!R|�tc����Jz�jϦ�gS>�, KL��tZ�>JY� ��N� ( �m���� :¹#�.�fe�/R��uX�HGe�oü}�Q�� �h[m�8VSrlk��)Ҝ%���9QA�,\��Z`��g��z����(_@-�C_;>!��N��̭V���!�wV-�L���9�&fm�/zI�7�2A��F_���G�Oy��,����bdո�q�P����ݨ��H��H��Uh�6���(F We've already accounted for that carbon atom from the peak at about 170. If it was an acid, you would already have used up both oxygens in the structure in the -COOH group. Carbon-carbon coupling is not observed because of the low abundance of the 13C isotope. Some internal (quaternary) aromatic. The carbon-oxygen double bond in the peak for the ketone group has a slightly lower value than the table suggests for a ketone. Chemical Shift Table 2 13C NMR Chemical Shift Peak Assignment for Functional Groups of Interest in Petroleum Chemistry. Here are the structure and the spectrum again: The easiest peak to sort out is the one at 28. The smaller the magnetic field needed, the higher the chemical shift. 140.0 120.0 130 110 215 200 180.0 165.0.

Alkyl (other than methyl) substituted aromatic.

Now, you may wonder why the neighboring carbons do not cause splitting since they resonate in the same frequency range. And that is why a technique called broadband decoupling is used. 43 Representative 13C Chemical Shifts 13C NMR Chemical Shift Correlations Type of carbon Chemical Shift ( ) ppm1 alkyl, RCH 3 0-40 2 10alkyl, RCH 2 R -50 3 alkyl, RCHR 2 15-50 4° alkyl, R 4 C 15-50 R 3 But because there are three peaks, the carbons must be in three different environments.

Here is the structure for 1-methylethyl propanoate: There are two very simple peaks in the spectrum which could be identified easily from the second table above.

The peak at just under 200 is …

In the spectrum there are a total of three peaks - that means that there are only three different environments for the carbons, despite there being four carbon atoms. Unless otherwise indicated, all were run at room temperature (24 ( 1 °C).

13.14 13C NMR Spectroscopy 1H and 13C NMR compared: both give us information about the number of chemically nonequivalent nuclei (nonequivalent hydrogens or nonequivalent carbons) both give us information about the environment of the nuclei (hybridization state, attached atoms, etc.) The peak at 67 is due to a different carbon singly bonded to an oxygen. << /Length 5 0 R /Filter /FlateDecode >> No two carbons are in exactly the same environment. ��ࡱ� > �� � � ���� � � ������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� ���� That’s why the scale ranges to negative ppm.

The alcohol is C. This follows on from Example 2, and also involves an isomer of C4H10O but which isn't an alcohol. relative to TMS: 220: 200: 180: 160: 140: 120: 100: 80: 60: 40: 20: 0-20: H 3 C-C- primary: H 3 C-S-: H 3 C-N: H 3 C-O--H 2 C-C secondary: Cyclopropanes-H 2 C-S--H 2 C-N-H 2 C-O- … There is an interaction between the carbon-oxygen and carbon-carbon double bonds in the molecule which affects the value slightly. And the peak at 26 is the methyl group which, of course, is joined to the rest of the molecule by a carbon-carbon single bond.

That means that the propanone spectrum will have only 2 peaks - one for the methyl groups and one for the carbon in the C=O group. It also includes NMR summary data on coupling constants and chemical shift of 1H, 13C, 19F, 31P, 77Se, 11B.

The signals in 200 ppm region are coming from carbonyl compounds. The one closer to the carbon-oxygen double bond has the larger value. Just like the 1H NMR, the reference point is the signal from TMS which again is set to 0 ppm. ��ŭ�8�Ǖ�t�VH�ġ�9t�O 4�Bq"������aZ>5Y%L��?��O;� �j��Y��>�4�V���kQ�

The only exception are the alkynes which are not so much downfield because of their magnetic anisotropy which we discussed earlier in the chemical shift post. to 3 decimals are experimental for IUPAC Standards; freq.

Because these are isomers, each has the same number of carbon atoms, but there is a difference between the environments of the carbons which will make a big impact on the spectra. Natural Molar Freq. o�L�[�Q�/`9��B9�Et��Fb�U� � FT0>�4����a� 9"�'J@�yDDh�E;֣]4�s;@��En}��@��"�O _34� Z2�b�C ,V���W1�� This is also known as 3-buten-2-one (amongst many other things!) Taking a close look at three C-13 NMR spectra. Chemical Shift Table 2 13C NMR Chemical Shift Peak Assignment for Functional Groups of Interest in Petroleum Chemistry. Protonated aromatic.

The C-13 NMR spectrum for 1-methylethyl propanoate. That means that you will need a smaller external magnetic field to bring the nucleus into the resonance condition than if it was attached to less electronegative things.

Notify me of followup comments via e-mail. We are only looking at the number of signals that each non-equivalent carbon atom gives as a single peak! In the table, the "R" groups won't necessarily be simple alkyl groups.

A few words about interesting features and exceptions in 13C NMR.