even-though-alkene-hydrogens-usually-show-up-at-similar-chemical-shifts-between-

Question

Even though alkene hydrogens usually show up at similar chemical shifts between 5 and 6 ppm, the chemical shifts of the labeled alkene hydrogens below are different (H_a = 6.009 ppm; H_b = 7.034 ppm). Rationalize the difference.

Accepted Answer

The carbon that bears H_b becomes electron-deficient when the π electrons delocalize, resulting in the de-shielding of H_b and a higher chemical shift.

Answer

The carbon that bears H_b becomes electron-rich when the π electrons delocalize, resulting in the shielding of H_b and a higher chemical shift.

Answer

The carbon that bears H_a becomes electron-deficient when the π electrons delocalize, resulting in the de-shielding of H_a and a lower chemical shift.

Answer

The carbon that bears H_b becomes electron-deficient when the π electrons delocalize, resulting in the shielding of H_b and a higher chemical shift.

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