Signal position
1H NMR spectra have signals in the range 0 - 12 δ, relative to the strong signal due to the twelve equivalent hydrogens in (CH3)4Si (tetramethylsilane, abbreviated as TMS) at 0 δ.
The exact position (chemical shift) of a signal due to a particular hydrogen depends on the electronic environment of that hydrogen. Elements or groups that withdraw electron density from around the hydrogen cause the 1H nucleus to absorb at lower field strengths (higher δ).
The position of the absorption depends on the type of carbon to which the hydrogen is bonded:
Furthermore, the exact position of the absorption of hydrogen(s) bonded to a saturated carbon depends on the properties of the other atom(s) or groups bonded to that carbon.
The exact position (chemical shift) of a signal due to a particular hydrogen depends on the electronic environment of that hydrogen. Elements or groups that withdraw electron density from around the hydrogen cause the 1H nucleus to absorb at lower field strengths (higher δ).
The position of the absorption depends on the type of carbon to which the hydrogen is bonded:
Hydrogens bonded to saturated carbons absorb between 0-5 δ.
Hydrogens bonded to doubly bonded carbons absorb between 5-12 δ.
Hydrogens bonded to doubly bonded carbons absorb between 5-12 δ.
Furthermore, the exact position of the absorption of hydrogen(s) bonded to a saturated carbon depends on the properties of the other atom(s) or groups bonded to that carbon.
As shown below, if another atom (or group) is doubly bonded to carbon, or is more electronegative than carbon (O, N or halogen), the hydrogen absorbs at higher δ.
The reference to Ar in the chart below refers to an aromatic ring like benzene. Ar-H is the H bonded directly to the benzene ring.
Ar-CH- is a hydrogen bonded to a carbon that is bonded to an aromatic ring.
The reference to Ar in the chart below refers to an aromatic ring like benzene. Ar-H is the H bonded directly to the benzene ring.
Ar-CH- is a hydrogen bonded to a carbon that is bonded to an aromatic ring.