Question

Research the H-NMR of a mixture of neral and geranial (citral) from the SigmaAldrich.om web site. Can you explain why there are differences, especially in the chemical shifts of the vinyl hydrogens

Answer 1

The different magnetic shielding effects of the carbonyl double bond in CH0, the CH₂ (a) and CH₂ (b) protons show different chemical shifts

Because the degree of shielding depends on electron density round the proton, the neighboring carbonyl group will increase this density in geranial form.

Now in CH₂ the electron density is increased around CH₂ (a) protons in neral form due to the carbonyl group, and thus it has a lower z values than the corresponding geranial form.

In the case of CH₃ (b) protons. thus they have lower z values and higher chemical shift than the corresponding nera form.

Step-by-step explanation:

Solution

Due to the different magnetic shielding effects of the carbonyl double bond in CH0, the CH₂ (a) and CH₂ (b) protons show different chemical shifts.

Since the degree of shielding depends on electron density round the proton, the neighboring carbonyl group will increase this density in geranial form more in case of CH₃ (b) protons. thus they have lower z values and higher chemical shift than the equivalent nera form.

Similarly, the electron density is increased around CH₂ (a) protons in neral form due to the carbonyl group, and thus it has a lower z values than the equivalent geranial form.