Deuterium‐induced isotope effects on 6Li chemical shifts, transmitted over two bonds, 2Δ(6Li)(2H/1H), have been measured for the first time for methyllithium and the system methyllithium/lithium iodide. The observed shifts are to low field and range from 15 to 20 ppb per CD3 group. The multiplicity and intensity distribution of the 6Li signals resulting for mixtures of CH3‐ and CD3‐containing samples in the limit of slow inter‐ as well as intra‐aggregate exchange yield information about the size of the various clusters present in diethylether solution. It is expected that these isotope shifts can facilitate structural investigations of organolithium compounds. In some cases, the results of such measurements are expected to be less ambiguous then the conclusions based on multiplets that arise from scalar 13C,6Li spin‐spin coupling.

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A homonuclear 6Li,6Li spin-spin coupling has been directly measured in the case of the dimer of (E)-2-lithio-1-phenyl-1-o-lithiophenylpent-1-ene. This constitutes the first direct observation of such a parameter. The well known INADEQUATE experiment in its one-and two-dimensional versions is applied for the first time to a spin system of spin-1 nuclei. It is demonstrated that the experiment is very sensitive for the detection of 6Li,6Li spinspin interactions, and thus provides a promising alternative to the COSY experiment and an additional tool for structural studies on organolithium compounds in solution.KEY WORDS 6Li,6Li NMR 6Li,6Li coupling INADEQUATE Recent research in the field of organolithium compounds has revealed a number of aggregates with two or even more chemically non-equivalent lithium Consequently, in the limit of slow inter-and intra-aggregate exchange, the 6Li NMR spectra of these systems display several distinct 6Li resonances. Direct Li-Li contacts or Li-C-Li structural units are then expected to yield observable 6Li,6Li spin-spin coupling transmitted over one or two bonds, but line splittings due to homonuclear 6Li,6Li interactions have so far, to the best of our knowledge, not been resolved. Attempts to detect heteronuclear 6Li,7Li coupling in alkyllithium compounds were also unsuccessful.6The first unequivocal evidence for the existence of scalar 6Li,6Li interactions came from the observation of cross-peaks in a 2D 6Li,6Li COSY spectrum.' The COSY pulse sequence, especially in its version optimized for long-range couplings of small magnitude'[COSY-LR, Eqn (l)], is a valuable tool when spin-spin coupling is hidden in the line width of 1D spectra, which is often the case for quadrupolar nuclei. Using COSY spectroscopy, in addition to 6Li,6Li interactions,' "B,11B8 and s1V,51V9 a s well as 'H,'H coupling constants" have been detected. 9Oo-t,-, A, 90°, A, FID(1)

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Dedicated to Professor Dr. Wolfgang Luttke on the occasion of his 75th birthday (13. IX. 95)The solution structure and the aggregation behavior of (E)-2-lithio-l-(2-lithiophenyl)-l-phenylpent-l-ene (1) and (Z)-2-lithio-l-(24ithiophenyl)ethene (2) were investigated by one-and two-dimensional 'H-, I3C-, and 6Li-NMR spectroscopy. In Et@, both systems form diniers which show homonuclear scalar 6Li,6Li spin-spin coupling. In the case of 2, extensive 6Li,'H coupling is observed. In tetrahydrofuran and in the presence of 2 mol of N,N,N',N'-tetramethylethylenediamine (tmeda), the dimeric structure of 1 coexists with a monomer. The activation parameters for intra-aggregate exchange in the diniers of 1 and 2 (1 (Et,O): A H # = 62.6 h 13.9 kJ/mol, AS # = 5.8 * 14.0 J/mol K, A G '(263) = 61.1 kJ/mol; 2 (dimethoxyethane): A H # = 36.9 h 6.5 kJ/mol, AS # = -61 h 25 J/mol K, AG # (263) = 54.0 kJ/mol) and the thermodynamic parameters for the dimer-monomer equilibrium for 1 (AHa = 26.7 f 5.5 kJ/mol, AS" = 63 * 27 J/mol K), where the monomer is favored at low temperature, were determined by dynamic NMR studies.Introduction. -Modern NMR spectroscopy provides a number of 1D-and 2D-pulse sequences which have paved the way for extended and more detailed NMR investigations of organolithium compounds, in particular of systems which contain several nonequivalent Li-sites [2-61. Apart from simple spin-echo spectroscopy [7] [8], 2D 6Li or 'Li-exchange spectroscopy (EXSY) [2], heteronuclear ID 'H, or 2D [lo] Overhauser measurements, and homo-as well as heteronuclear shift correlations of the hLi,6Li [ 1 11 and 'Li,I3C [I21 type are of great importance. In favorable cases with regard to line width and relaxation behavior, even 7Li,7Li-COSY [ 131 and iH,7Li-Overhauser measurements [14] could be performed. In addition, information about the aggregation states of organolithium compounds can be obtained from deuterium-induced isotope shifts of the 6Li-resonance [ 151.In the following we report results from the application of a number of these NMR techniques to two 6Li-labelled dilithiostyrene compounds, (E)-2-lithio-1 -(2-lithiophenyl)-1 -phenylpent-1-ene (I) [16] and (Z)-2-lithio-l-(2-lithiophenyl)ethene (2; arbitrary numbering) [ 171. These systems are related to (E)-l-lithio-2-(2-lithiophenyl)-l-phenylhex-l-