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The 3Adeuterium isotope effects of partially and fully deuteriated tert-butyl groups on the 13C NMR spectra of tert-butylbenzene and derivatives are discussed in detail. It is shown that they correlate with the chemical shift of C-1 of the aromatic ring. It has been demonstrated that when deuterium is replaced with some other substituents, the SCS values of these substituents show a parallel behaviour to the deuterium isotope effects. It is concluded that, for the compounds studied, deuterium isotope effects and substituent chemical shifts can be described on a common basis.

Four differently substituted phenylallyllithium compounds Li . 2 have been investigated by dynamic 'H-and I3C-NMR, NOESY and HOESY spectroscopy. It is shown that a considerable barrier of rotation (ca. 40 kJ/mol) between the phenyl and the allyl moiety exists which is only slightly affected by the addition of TMEDA. The lithium atom prefers a bridged position with respect to the allylic part in solution and has HOESY contacts to the ortho hydrogen atoms of the aromatic ring.The structure of allyllithium compounds is of fundamental interest and has been extensively investigated in the current literature[''. Schlosser[21 used the method of isotopic perturbation of equilibrium to conclude that allyllithium forms an unsymmetrical q3 complex. Schleyer, who used the same technique, first described a symmetrically bridged structurer3], later, however, his group has found that the asymmetric species in THF is a dimer14]. Fraenkel extensively applied l3C-NMR spectroscopy of 6Li-labelled compounds and reported recently on the conformation and dynamic behavior of trimethylsilyl-substituted allyl anion^ [^,^]. To allyllithium a "chameleon behavior" has been ascribed"], with an ionic and covalent form in an equilibrium. Weissr8' succeeded in crystallizing the first allyllithium stabilized by TMEDA, and Bochel9] showed that in the solid state the compound is an q3 complex. Further light on the structure of allyl anions was shed by an investigation of carbon-carbon coupling constants"'] and very recently by a theoretical comparison of different alkali metals[111, and calculations of NMR spectra using the IGLO approach have been communicated['']. With modern NMR methods such as NOESY and HOESY spectroscopy it should be possible to assess the structure of these compounds in solution. We have therefore started an investigation to completely characterize some allyllithium compounds by means of these NMR methods. Our choice centered on allyllithium compounds with one phenyl substituent, since these anions are relatively simple to prepare, rather stable, and to our knowledge no stringent NMR analysis has been presented. Results and Discussion PreparationThe allyl anions 2a-c have been prepared by reaction of the corresponding vinyl bromides 1 a -c with n-butyllithium in hexane. The compounds Li . 2 were obtained in crystalline form and were, after washing with dry n-hexane, transferred under argon into the NMR tube. Upon subsequent dissolution in [DJTHF the vinyllithium compounds underwent the transformation described by Knorr and Lattke[l3]. 2d was obtained directly by hydrogen abstraction from olefin 3 as shown in Scheme 1 [I4]. We restrict the detailed description of the NMR spectra to 2a. The data of the other compounds are rather similar and given in tabular form.