How Do We Solve an NMR Problem

One of the first steps in determining the molecular structure of a compound is to establish the compound s molecular formula. In the past, this was most commonly done by elemental analysis, combustion to determine the percent composition, and so forth. More commonly today, we determine molecular weight and molecular formula by a technique known as mass spectrometry (an explanation of the technique is beyond the scope of this book). In the examples that follow, we assume that the molecular formula of any unknown compound has already been determined, and we proceed from there, using spectral analysis to determine a structural formula. 

The following steps may prove helpful as a systematic approach to solving H-NMR spectral problems  

Step 1 Molecular formula and index of hydrogen deficiency. Examine the molecular formula, calculate the index of hydrogen deficiency (Section 11.4G), and deduce what information you can about the presence or absence of rings or pi bonds. 

Step 2 Number of signals. Count the number of signals to determine the minimum 

Step 3 Integration. Use signal integration and the molecular formula to determine the 

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