Proton NMR Chemical Shifts and Neighboring Group Effects

Vocabulary flashcards covering characteristic chemical shifts of protons in different electronic environments and the quantitative effects of neighboring functional groups on alpha and beta protons.

Methyl proton ($\text{R-CH}_3$) chemical shift

Has an expected chemical shift of approximately $\delta ∼ 0.9$.

Methylene proton ($\text{-CH}_2\text{-}$) chemical shift

Has an expected chemical shift of approximately $\delta ∼ 1.2$.

Methine proton ($\text{-CH-}$) chemical shift

Has an expected chemical shift of approximately $\delta ∼ 1.7$.

Allylic proton chemical shift

Has an expected chemical shift of approximately $\delta ∼ 2$.

Alkynyl proton chemical shift

Has an expected chemical shift of approximately $\delta ∼ 2.5$.

Aromatic methyl proton chemical shift

Has an expected chemical shift of approximately $\delta ∼ 2.5$.

Alkyl halide proton chemical shift

Has an expected chemical shift in the range of $\delta\, 2 - 4$.

Alcohol proton ($\text{R-O-H}$) chemical shift

Has an expected chemical shift in the range of $\delta\, 2 - 5$.

Vinylic proton chemical shift

Has an expected chemical shift in the range of $\delta\, 4.5 - 6.5$.

Aryl proton chemical shift

Has an expected chemical shift in the range of $\delta\, 6.5 - 8$.

Aldehyde proton chemical shift

Has an expected chemical shift of approximately $\delta ∼ 10$.

Carboxylic acid proton chemical shift

Has an expected chemical shift of approximately $\delta ∼ 12$.

Alpha proton effect: Oxygen of an alcohol or ether

Increases the chemical shift of alpha protons by an adjustment of $+2.5\,\text{ppm}$.

Beta proton effect: Oxygen of an alcohol or ether

Increases the chemical shift of beta protons by an adjustment of $+0.5\,\text{ppm}$.

Alpha proton effect: Oxygen of an ester

Increases the chemical shift of alpha protons by an adjustment of $+3.0\,\text{ppm}$ ($+3\,\text{ppm}$).

Beta proton effect: Oxygen of an ester

Increases the chemical shift of beta protons by an adjustment of $+0.6\,\text{ppm}$.

Alpha proton effect: Carbonyl group ($\text{C=O}$)

Increases the chemical shift of alpha protons by an adjustment of $+1.0\,\text{ppm}$ ($+1\,\text{ppm}$).

Beta proton effect: Carbonyl group ($\text{C=O}$)

Increases the chemical shift of beta protons by an adjustment of $+0.2\,\text{ppm}$.

Beta proton chemical shift general rule

The neighboring group effect on beta protons is generally about one-fifth ($\frac{1}{5}$) of the effect on the alpha protons.