Two types of protons in ferrocene

Abstract

Two absorption bands of ferrocene, the in-plane bending C-H vibrations (β_CH) at 1002 cm⁻¹ and out-of-plane C-H vibration (γ_CH) at 816 cm⁻¹, are accompanied with high-frequency satellites β_CH (1055) and γ_CH (837 cm⁻¹). In the spectrum of 1,1′-dideuteroferrocene, only the high-frequency bands suffer an isotopic shift, from 1055 to 859 cm⁻¹, and from 837 to 668 cm⁻¹. Only additional incorporation of deuterium into 1,1′-dideuteroferrocene results also in an isotopic shift of the basic bands: 1002 to 771 and 816 to 632 cm⁻¹. Therefore, one of the five carbon atoms of cyclopentadienyl ring of ferrocene differs from the other in the static state. It is assumed that just this carbon atom is bonded with the iron atom by the σ-bond.