The proton magnetic resonance spectrum of triptycene. The effect of magnetic anisotropy on the proton shifts

Abstract

The ring proton spectrum of triptycene (2.2 mole % in CS2) was analyzed after the methine proton was decoupled. The modified ring current model accounts for most of the internal shift. Bond anisotropies and electron density contributions are also present. The latter account for the mean proton shift. The agreement between the predicted and calculated shifts is excellent for the proton meta to the methine substituent, but a discrepancy of 0.1 p.p.m. is found for the ortho proton. Correction for the ring anisotropy effects produces excellent agreement of the methine proton shift with the empirical correlation between the C—H proton shifts and the 13C–H coupling constants. The ring proton–proton coupling constants are little different from those in benzene, but a small strain in the bonds near the methine carbons is implied.

The Preparation of Some Heterocyclic Analogues of Triptycene

“…spectra of these compounds are consistent with their analyses and properties. The methine protons give sharp singlets in a similar range to those found for triptycene (17,18) and for a thiophene analogue (2). Values, however, for the compounds with phenyl substituents on the thiophene ring, lie at slightly lower field, probably due to the deshielding effects of the phenyl groups.…”

The Effect of Bulky Substituents on the Formation of Symmetrically Trisubstituted Triptycenes

“…They described the typical patterns for the aromatic protons as well as the two singlets generated by the bridgehead protons. It is also mentioned by Kidd et al [18] that the shifts of these singlets depend on the aromatic substituents and that the bridgehead proton of the syn-isomer experiences a larger shift ∆δ than that of the anti-isomer. In general we approve these results, but found in addition that in the case of the modified 1,8,13-trichlorotriptycenes, due to the close arrangement of three chloro functions, the corresponding bridgehead proton, pointing to the same side as the chloro substituents, is so strongly deshielded that its signal overlaps with the proton signals of the aromatic system.…”

Aromatic ring currents in benzotriptycenes, studied by high‐resolution deuterium NMR at high fields

“…Indeed, it has been shown that the proton shifts in the benzotriptycenes can be rationalized without the assumption of reduced ring currents, by taking into consideration other shift contributions. 8 It should also be noted that this work does not support the once-mentioned idea of a circular current perpendicular to the ring faces in the benz~triptycenes.~ Such an 'around the barrel' flow of r-electrons would tend to decrease the absolute value of Ax. This type of ring current has also been rejected on theoretical ground^.^,^…”