The chemical environment of protons can be deduced from their chemical shifts. W

Question

The chemical environment of protons can be deduced from their chemical shifts. What are the relative chemical shifts of the protons at the labeled positions? [Protons that are highly shielded have low delta (chemical shift) values.] 1) lhe proton with the lowest delta value (the most shielded) is The proton with the highest delta value (the most deshielded) is 2) ?? OCH3 The proton with the lowest delta value (the most shielded) is The proton with the highest delta value (the most deshielded) is

Explanation / Answer

1) The proton with lowest delta and hence most shielded is Proton b. of the hydrogen atom.

Electronegativity of Oxygen is the maximum, followed by the electronegativity of Nitrogen and then Carbon. Proton b is farthest away from oxygen and hence the electronegativity effect decreases with increasing distance.Therefore, proton b of the hydrogen atom is most shielded thereby having a lower chemical shift.

The proton with highest delta and therefore being most deshielded is the proton c.

Proton c is farthest from the oxygen and hence it possesses high chemical shift.

2) The proton with lowest delta value in the second problem is proton a .

It is because proton a is most far away that of oxygen.

The proton with highest delta is proton b.

It is because proton b is farthest away from oxygen.

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