Upon assigning $\ce{^{13}C}$-NMR for 1,1'-bis(α-methylmethanol)ferrocene, we discovered the substituted FcC-CH peak (95.14 ppm) was more downshifted than the CH-OH peak (65.59 ppm) as was confirmed by HSQC. The other four FcCH peaks were found at 67.77, 67.67, 66.12 and 66.07 ppm.

I can't rationalise why the FcC-CH peak is so downshifted as the lone pairs of oxygen can't donate in via resonance and if it was purely inductive, surely the CH-OH peak would be further downshifted.

Upon transformation to 1,1'-bis(α-methoxyethyl)ferrocene and then 1,1'-bis((α-methyl)methylpropanoate)ferrocene, the FcC-CH peak was still seen to be further downshifted than I expected.

If anyone can offer an explanation, I'd be very grateful!


1 Answer 1


First of all, electronic effect on $\ce{^{13}C}$-chemical shifts of 1,3-cyclopentadiene $(\pu{132.2 ppm}, \pu{132.8 ppm})$ is well evident due to the iron metal in ferrocene $(\pu{67.7 ppm})$. Yet, when ferrocene is substituted with any group, the $\ce{^{13}C}$-chemical shift of the carbon attached to the substituent shows a blue shift. I think this seemingly large blue shift in $\ce{C}$1 of the substituted ferrocenes is due to the sheilding-deshielding effects due to steric hindrance (similar to chemical shift difference shown in cis- and trans-alkenes). The same effect we have usually shown in substituted benzenes as well. I also think this chemical shift difference in $\ce{C}$1 of substituted ferrocenes is not too much of a difference than that shown in substituted benzenes:

substituted ferrocene vs substituted benzene

For example, when $\ce{R = CH3}$ (see above structures), $\ce{^{13}C}$-chemical shift of $\ce{C}$1 of ferrocene is $\pu{83.4 ppm}$ $(\Delta\delta = \pu{15.7 ppm})$ while that of substituted benzene is $\pu{137.4 ppm}$ $(\Delta\delta = \pu{9.3 ppm})$ where $\Delta\delta =$ $\ce{C}$1 of unsubstituted - $\ce{C}$1 of substituted (Ref.1).
Similarly, when stereo bulk is increased, say $\ce{R = C(CH3)3}$, then $\ce{^{13}C}$-chemical shift of $\ce{C}$1 of ferrocene is increased to $\pu{101.7 ppm}$ $(\Delta\delta = \pu{34.0 ppm})$ while that of substituted benzene is $\pu{150.5 ppm}$ $(\Delta\delta = \pu{22.4 ppm})$ (Ref.1).
Also, in a compound related to OP's mentioned compound where $\ce{R = CH2OH}$, the $\ce{^{13}C}$-chemical shift of $\ce{C}$1 of ferrocene is given as $\pu{87.7 ppm}$ $(\Delta\delta = \pu{20.0 ppm})$ while that of the substituted benzene is $\pu{141.1 ppm}$ $(\Delta\delta = \pu{13.0 ppm})$ (Ref.1).

There are few other examples in Ref.1 suggests that the difference in this chemical shift is due to the stereo hindrance. Also keep in mind that extra large $\Delta\delta$ shown in ferrocenes are due to the electronic influence from the iron metal.


  1. A. A. Koridze, P. V. Petrovskii, A. I. Mokhov, A. I. Lutsenko, "Electronic effects in the cyclopentadienyl ring. The $\ce{^{13}C}$ NMR spectra of monosubstituted ferrocenes," Journal of Organometallic Chemistry 1977, 136(1), 57-63 (DOI: https://doi.org/10.1016/S0022-328X(00)87967-X).

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