# Why is H in OH group is more shielded than in H in CH2 group (ethanol NMR spectroscopy)?

I am confused with this $$\mathrm{^1H}$$-$$\mathrm{NMR}$$ spectroscopy result:

Shouldn't $$\ce{H}$$ in $$\ce{OH}$$ group the singlet be more towards the left of the $$\mathrm{NMR}$$ spectrum?

It is near the highly electronegative atom $$\ce{O}$$ rather than the two $$\ce{H}$$ in $$\ce{CH2}$$ group they have a weak eletronegative atom $$\ce{C}$$ so it shouldn't be that desheilded.

• What about that same $\ce{CH2}$ attached to very electronegative $\ce{O}$ atom? Jun 30 '20 at 22:27
• But the two H's has to throw the C atom and they see the O atom but in H in OH group its directly next to it. Jul 1 '20 at 4:33
• Exactly, it's directly next to the electron-rich O atom. Jul 1 '20 at 5:52
• Electronegativity is not the only thing matter here. Jul 1 '20 at 6:01

It is a myth that electronegativity is the only things that effect chemical shifts. However, electronegativity is only one of many things that effect chemical shift of a proton. Other things effecting chemical shift are magnetic anisotropy (e.g., large deshielding effects on aromatics and alkenes), steric compression (e.g., measurable $$\Delta \delta$$ values of alkene protons on cis- and trans-isomers), anisotropy of double bonds (e.g., measurable positive $$\Delta \delta$$ values of methyl group of methylcyclohexene and methylcyclohexane, $$\delta_{\mathrm{sp^2}(\ce{CH3})}-\delta_{\mathrm{sp^3}(\ce{CH3})} \approx 1.60-0.92= 0.68$$), solvent effects, etc.
All of above mentioned factors effect chemical shifts of proton attached to electronegative atom such as $$\ce{OH}$$ and $$\ce{NH}$$. In addition, solvent used and solute concentration are also fators changing chemical shifts of these protons. For example, let's consider alcohol $$\ce{OH}$$ protons. In dilute solution of alcohols in non-hydrogen-bonding solvents such as $$\ce{CCl4, CDCl3,}$$ and $$\ce{C6D6,}$$ the $$\ce{OH}$$ signal generally appears at $$\delta \ 1\!- \!2$$. For instance, residual peak in $$\ce{CDCl3}$$ is always appeared at around $$\delta \ 1.6$$. At higher concentrations in non-polar solvents, the $$\ce{OH}$$ signal moves downfield ($$+\delta$$) because when concentration increase, the $$\ce{H}$$-bonding increases as a result. For instance, the $$\ce{OH}$$ signal of ethanol comes at $$\delta \ 1.0$$ in a 0.5% solution in $$\ce{CCl4}$$, and it appears at $$\delta \ 5.13$$ in the pure ethanol (5-HMR-2 Chemical Shift):
The solvent used to take the given spectrum is unknown. Based on the chemical shift of $$\ce{OH}$$ signal, one can assume solvent might be $$\ce{CDCl3}$$, which is the most common among NMR solvents, which does not promote $$\ce{H}$$-bonding. As you can judge by the image above, it might have taken in the concentration of 1-5% range.