X-ray photoelectron spectroscopy (XPS) has been utilised to investigate the influence of poly(ethylene glycol) (PEG) substituents on fundamental interactions in ionic liquids (ILs). A series of monocationic and dicationic PEG-functionalised IL systems that are based upon imidazolium, pyridinium and pyrrolidinium cation have been investigated. A robust C 1s fitting model has been developed for all PEG-functionalised ILs investigated and comparison made to their alkyl substituted analogues. A systematic study of the PEG-functionalised IL has revealed a significant difference in the electronic structures of the compound where the first oxygen in an alkyl is moved from the Beta to the alpha position. In the absence of a robust alkyl chain substituent, a new method for charge referencing IL core binding energies was developed. While an investigation into the BEs of a series of PEG-functionalised chlorozincate(II)-based systems with respect to their alkyl substituted analogue, as probe of Lewis acidity, indicated similarity in BEs. Therefore, suggesting that both IL set can be employed in predicting the Lewis acidity of IL systems.