Interpretation of H-NMR Spectra

There is a lot of information in a NMR spectrum. The following series of steps provides an effective procedure for using this information to determine the structure of a compound  

Step 2. Examine the integral for the ratios of the different kinds of hydrogens. Remember that the actual numbers can be multiples of these ratios. If the formula is available, determine the actual numbers. 

Step 3. Examine the coupling patterns. This is often the most important step because it enables fragments of the compound to be identified. The number of peaks in the signal for a particular hydrogen(s) tells how many hydrogens are nearby. Remember that there is one less nearby hydrogen than the number of peaks that is, if a signal is split into four 

Step 4. Construct a tentative structure. At this point, various fragments have been identified from the coupling patterns, the chemical shifts, the IR spectrum (if available), the formula, and so on. Assemble these fragments into a tentative structure. 

Step 5. Determine whether all of the information is consistent with this structure. 

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Interpretation of H NMR spectra is based on consideration of three interrelated types of information integration of signal peaks, chemical shift, and spin-spin coupling. Integration of the signal peaks provides the ratio of hydrogen atoms in the compound. The concept... 

Bonds that rotate rapidly at room temperature do not have a fixed angle between adjacent C—H bonds, so an average angle and an average coupling are observed. This latter concept is important for the interpretation of H-NMR spectra for alkanes and other flexible molecules. 

Lounasmaa et al. (51,53,148,149) have recorded and interpreted the H-NMR spectra of several 4-benzyltropane alkaloids and their hydrolysis... 

These results suggest that in the pentitols and hexitols, at least, the intermolecular H-bonds have only a secondary influence on the shape of the molecules in the solid state. The observed conformations in the solid state can be rationalized (16) in terms of the intramolecular interactions between hydroxyls which are believed to involve energies of the order of several kilocalories (27) (the interpretation of the NMR spectra of acetylated acyclic sugar derivatives in solution is based on the same type of hypothesis (29)). 

The spectral analysis is carried out manually because automatic interpretation and library programs are normally not available. Difficulties in NMR and automatic interpretation are (a) high spectral background in spectra recorded from environmental samples, often leading to resonance overlap, (b) solvent dependence of chemical shifts (8), which with couplings affects the appearance of the spectrum, and (c) in the case of H NMR spectra, the complexity. The other spectra, particularly 13C H, are simple, but low sensitivity is then a problem. 

The (dxyf(dxz,dyzf electron confignration gives rise to H NMR spin delocalization to protons on the -pyrrole snbstitnents of the molecnle via the filled 3e(7t) porphyrin orbitals, that is P Fe tt bonding, which is symmetry-allowed. The interpretation of the NMR spectra in... 

As a matter of routine in your laboratory work you will be required to interpret H—NMR spectra (also known as proton spectra). -NMR spectra are becoming more common, while F and spectra may be obtained in specialized experiments. Therefore you should concentrate on the interpretation of H and spectra in the first instance. 

The analysis of a full tilt series of H NMR spectra not only allows the determination of the unique bond angle for a deuteriated methyl group, but also provides an internal check for the consistency of the spectral interpretation. In particular, simulations provide a means for the analysis of line-broadening effects, which arise from the sample mosaic spread as well as the intrinsic line width of the nuclear transition and instrumental factors. When line shapes are fitted to a full tilt series of spectra in a concerted manner and are also compared with the powder spectrum of an unoriented sample, the different contributions can be discerned. In that way an intrinsic line width of around 2 kHz is found for the spectra shown here, together with a mosaic spread between 8° and 10° for the three samples. 

Hence only the contact shift is important in interpreting the H NMR spectra of cubane cluster Fd. The contact shift for nucleus i, ligated to iron q, can be written in general as ... 

The ability to obtain chemical shifts from H spectra, without resorting to spectral simulation, is a useful first step towards the Interpretation of complex NMR spectra (1). In spectra the coupling between magnetically equivalent nuclei is not manifest (3). By substitution with a deuteron, the J( H, H) can be determined, as for methanol (Figure 4), and the corresponding J( H, H) calculated according to eq. 1 (1,2). 

Interpretation of H and 13C NMR spectra has been a part of almost all synthetic work on heteropyrans. Complete assignments using 2D NMR or other more advanced techniques still seem to be exceptional [92JCS(P2)1301]. Typical values of H and 13C NMR characteristics for some 2H- and 4//-heteropyrans are given in Tables V, VI, VII, and VIII. 

Studies of hydrosilation with trichlorosilane-d (2f) proved that exchange can also take place between SiD and C—H bonds in olefins during hydrosilation. Isobutylene was chosen as the olefin for this study because both it and isobutyltrichlorosilane have H NMR spectra that are easy to interpret, and because movement of the double bond can give rise to no detectable isomerization. Excess trichlorosilane-d with isobutylene and chloroplatinic acid was sealed into a Pyrex tube and kept near 25°C overnight. Deuterosilation was complete in less than 1 hour. Analysis of the product after about 16 hours indicated reactions that can be summed up as follows ... 

C NMR of the carbonyl groups also is consistent with this latter step, but may equally be interpreted as involving a rotation of the olefin about the metal triangle, a process not envisaged to occur with the 1 1 adducts (96). A recent study of the H-NMR spectra, particularly of the methylene protons of the 1 2 adduct formed by indene and Os3(CO)12, also indicates a rotation of the olefin fragment about the metal triangle (97). 

The increasing metal effect discussed for the series Zn/Ni/Pd/Pt in Section 4.2 was attributed to an increase of metal-to-porphyrin 7r-bonding merely by an interpretation of optical data the H-NMR spectra (53, 97) of the corresponding octaethylporphy-rin derivatives are not useful for this purpose, because they are also influenced by... 

Introduction of a-substituents into the 3- or 7-position of 12a leads to a shift of the prevailing conformation from chair-chair (cc) to boat-chair (be), and finally to twist double boat (16) as judged by H NMR spectra (121). The changes in the H H coupling constants in these derivatives can be interpreted with skewed cc conformations as well. MM calculations, however, ruled out the latter possibility (121). The results of acetolysis of exo- and endobicyclo[3.3.1]nonan-3-yl tosylates were also interpreted with the aid of MM calculations (122). 

C NMR spectra. The last group of problems (311-332) are of a different type and deal with interpretation of simple NMR spin-spin multiplets. To the best of our knowledge, problems of this type are not available in other collections and they are included here because we have found that the interpretation of multiplicity in H NMR spectra is the greatest single cause of confusion in the minds of students. 

The structural and photophysical properties of [Ru(bp 2(dafo)] PF6]2 (dafo = 93) have been reported the emission lifetime of the complex is 420 ns the study has been extended to the properties of the series of complexes [Ru(bpy) (dafo)3 J +. The nonplanar ligands (94) have been prepared, and form complexes of type [Ru(bpy)2(94)] for = 2, 3 or 4, and l Ru(bpy)2 2(94)]" for = 3 or 4. By using deuterated bpy ligands, more easily interpretable H NMR spectra are obtained. For the diruthenium complexes, there is limited inter-metal communication. ... 

The H NMR spectra of allyhnagnesium compounds display simple AX4 patterns at temperatures as low as —80 to — 120°C . Such simple spectra can be interpreted in terms of either rapidly interconverting a-bonded aUylmagnesium species or an essentially ionic species, with rapid rotation about the C—C partial double bonds. 

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