Question

How can you know if there is a doublet of doublets by looking at a structure?

Answer 1

Hint: The answer is based on the nuclear magnetic resonance spectra that is NMR spectra and the comparison of the proposed structure to that of the proton – NMR spectrum ${{(}^{1}} HNMR)$

Complete step by step answer:
- In the lower classes, we have come across the concepts of the various spectroscopic techniques that are used for the elucidation of the structure of the given molecule and also identification of the mass of the compound and related parameters.
Let us now see in detail about what does doublet of a doublet mean and how can that be identified by looking into a structure.
- Any organic compound which exists is confirmed through the $^{1}HNMR$ and $^{13}CNMR$ and it should have the accurate combustion analysis which is nothing but the $%C,H,N$ microanalysis.
- The organic compound should also have accurate boiling and melting points.
- Now, the compound can be identified if it has doublet or doublets by comparing the proposed structure with the experimental $^{1} HNMR$ spectrum.
- A doublet of doublet which is denoted as ‘dd’ is a pattern of four lines which are of approximate equal intensity that results from the coupling of two different protons.
The structure looks as shown below,

- The expected ‘dd’ splitting can be in vinyl groups or the 1,3,4-tri substituted benzenes.
Thus, the given structure is to be compared with the proton NMR and then the information of the presence of doublet of a doublet can be identified.

Note: Note that NMR spectroscopy is a powerful tool in the analytical chemistry branch today and condensed matter science as well for the purpose of elucidation of structure and dynamics of macromolecules.