Inductive Effects on Chemical Shift: Overview

Due to their shielded protons, the chemical shifts of unsubstituted alkanes lie below δ 1.8.

Electronegative substituents like chlorine withdraw the electron density away from the protons, increasing their chemical shift. Progressive substitution by chlorine shifts the proton signals further downfield.

The chemical shift also increases with the electronegativity of the substituent halogen.

The influence of an electronegative substituent is strongest at the alpha position and decreases with distance, becoming negligible at the gamma position.

Hybridization, delocalization, and hydrogen bonding also influence the electron density around protons. 

Due to their greater s-character, sp² hybridized carbons are more electronegative than sp³ hybridized carbons.

As the bonding electrons shift toward the sp² hybridized carbon, vinylic hydrogens are deshielded. So, protons in ethene resonate at δ 5.28, compared to δ 0.86 for ethane.

Similarly, delocalization of electron density in vinyl ether increases the shielding and lowers the chemical shift of the beta-hydrogens.

Protons involved in hydrogen bonding are highly deshielded and exhibit a range of δ values.