COSY cross peak correlations

In a COSY spectrum, a H ¹ spectrum is shown along both horizontal and vertical axes, and the intensity of correlation peaks is shown as mountains.

 The important information from the COSY spectrum comes from the correlation peaks (mountains) that appear off the diagonal (cross peaks). If we start at a given cross peak and imagine that two perpendicular lines lead back to the diagonal, these lines are coupled to each other. 

The intersepted peaks indicate that they are coupled to each other. It is found that the cross peaks above the diagonal are found symmetrically so only cross peaks on one side of the diagonal need to be interpreted.

Example : COSY spectrum of geraniol

1. Basic COSY spectrum of geraniol, in CDCl₃ at 500 MHz

 From the basic COSY spectrum, we can see that H-5 and H-6 are coupled by each other. However, the signals for 3 methyl groups at C-8, C-9, and C-10 are severely overlaped, as are those for the 2 methylene groups at C-4 and C-5. Moreover, it lacks of the H-1----H-4
and H-6----H-8 couplings, and the differentiation between H-8 and H-9 is uncertain.

 These problems can be less by using a double quantum filtered COSY (DQFCOSY); the intense singlets of noncoupled methyl groups are greatly reduced.

2. The DQFCOSY spectrum of geraniol, in CDCl₃ at 500 MHz

 In the DQFCOSY spectrum, we can see that the H-8 and H-9 methyl proton signals are clearly separated. The long-range coupling of H-8 and H-9 methyl groups with one another and the H-1----H-4 and H-6----H-8 couplings are present. However, the differentiation between H-8 and H-9 is still uncertain.