The NMR Spectra of the Ortho-and Para-Adamantyl Groups of Anisole

The 1-adamantyl group because of its rigid diamondoid st has three chemically distinct sets of protons. When substitu a benzene ring¹ the chemical shifts of the different sets of would be affected to different extents by the ring current eft the aromatic ring and by the electrostatic field effect³ of any proximate electronegative substituent. The nmr spectrum of the 1-adamantyl group of p-adamantyl anisole in chloroform solution sho three broad bands with unresolved fine structure at δ 2.08 (3H, γ protons), δ 1.89 (6H, β protons) and δ 1.75 (6H, δ protons), whereas in the case of o-adamantyl anisole the corresponding spectrum shows two broad bands at δ 2.10 (9H, β and γ protons) and δ 1.77 (6H, δ protons), as shown in the Figure. It is to be noted that the chemical shift of the β-protons of the o-adamantyl group is 0.20 ppm downfield from that of the p-adamantyl group. Clearly, this difference arises from the electrostatic field effect of the methoxyl on the β-protons of the o-adamantyl group. 1-Adamantyl substitution ortho to an electronegative substituent is therefore easily distinguished from the para case on the nmr spectrum.