The carbon 1s binding energies (E b ) measured by X ray photoelectron spectroscopy or obtained from quantum chemical calculations for 18 series of compounds in which the reaction center is the C atom are analyzed. It was established for the first time that E b values in carbon centered radical cations depend on the inductive, resonance, and polarizability effects of sub stituents.Key words: carbon 1s binding energy, inductive effect, conjugation, polarizability effect of substituents.The photoelectron and X ray electron spectroscopies (PES and XES, respectively) are widely used to study the ionization energies E of the electronic levels of molecules (see, for example, Refs 1-10). The gas phase PES and XES are based on the reaction ,where R C BX is a neutral molecule, R C •+ BX is a radical cation, X is substituent, and е -is an electron.The ionization energy E is equal to the total energy difference between the radical cation and the moleculeWithout loss of generality, we consider that the R C BX molecules form reaction series. Each series contains an invariable reaction center R C , the bridge В, and variable substituents X (in the R C X series, there is no bridge be tween R C and X). Detachment of an electron by reaction (1) occurs only from R C . Therefore, the formation of R C •+ BX or R C •+ X radical cations does not involve direct photoionization of orbitals of the substituents X.Photoelectron spectroscopy is used to determine the energy E (ionization potentials I) of valence electrons. The radical cation R C •+ BX is formed upon detachment of an outer (valence) electron from R C under the action of photoelectrons hν with energy of about tens of electron