How do I interpret NMR data

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Procedure for evaluating 1H-NMR spectra

In the following, the strategy is explained to evaluate a proton NMR spectra and to determine the molecular structure with the help of the chemical shift, the coupling pattern and the integral intensities. The individual steps (2-6) are explained in more detail in the following chapters.

Note
In practice, depending on the problem, several analytical methods are often used to fully clarify the structure in order to facilitate and also to secure the evaluation. Every chemist working in preparative work will certainly appreciate the fact that, in addition to the NMR spectra, the results of an elemental analysis (empirical formula) or the mass spectrum or IR spectrum are available.

Evaluation steps:

  1. The number of groups of equivalent protons can be deduced from the number of resonance signals.
  2. Determination of the chemical shift of the individual signals first attempts at assignment - chemical shift - structural elements
  3. Evaluation of the splits caused by the indirect spin-spin coupling and determination of the multiplicity of the signals in 1st order partial spectra; Comparison with the typical splitting pictures Statements about coupled proton groups
  4. Evaluation of the integral intensities of the individual signals, since the area below the signal is proportional to the number of nuclei that generate this signal, conclusions can be drawn about the proton ratio in the molecule.
  5. Linking of the individual information 1-4 Clarification of the molecular structure, possibly with the aid of additional analytical information (molecular formula, mass spectra)
  6. Use of incremental systems as an aid for the assignment of signals

Connection with empirical formula C9H12O

The best way to evaluate the spectra is to create a table where all relevant information is entered.

Tab. 1
Information for spectra evaluation
signal12345
δ in ppm1,382,273,98 6,797,05
MultiplicityTriplet Singlet QuadrupletHigher order multiplet Higher order multiplet
Intensity ratio3 322 2

Five signals appear in the spectrum, i.e. five groups of equivalent protons.

The results are discussed in the following chapters.