One‐bond ¹³C¹³C spin–spin coupling in cubanes

Abstract

Endocyclic one-bond 13C-13C spin-spin coupling constants in a series of cubane derivatives were recorded. The values measured using the INADEQUATE pulse sequence were found t o b e insensitive t o the nature of the substituent, fall in a narrow range (27-30 Hz) and are comparable to values reported for similar cyclobutane derivatives. KEY WORDS Cubanes 13C-13C spin coupling INADEQUATE

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants: 3. Polyhedranes

“…94 Also, the outer valence ionization potentials, low-lying electronically excited states and nuclear spin-spin coupling constants of cubane have been investigated at the ab initio level by using the outer valence Green function, RPA and equations-of-motions approaches which incorporate the main portion of the electron correlation effects. 95 Notwithstanding extensive studies of cubane by a variety of physical methods, no direct measurement of J(C,C) in unsubstituted cubane has been performed so far, although a very accurate experimental estimation of J(C,C) D 29.4 Hz can be gained from a paper by Axenrod et al, 8 who showed that J(C,C) of the cubane moiety is fairly insensitive towards the nature of the substituents in the series of polysubstituted cubanes. This is fairly close to ¾30-31 Hz, as follows from the present SOPPA calculations.…”

“…Only a rough estimation of experimental J(C,C) values between chemically bonded carbons in tetrahedrane of ¾9 Hz could be obtained from the corresponding tetra-tert-butyltetrahedrane data 7 and of ¾30 Hz in cubane from a paper by Axenrod et al,8 who measured J(C,C) in the series of substituted cubanes. The latter could undoubtedly be regarded as positive whereas the sign of the former is still unknown and remains dubious.…”