2416
A. Arduini et al. / Tetrahedron 57 (2001) 2411±2417
3. Conclusions
ments for all non-hydrogen atoms. The hydrogen atoms
were set in their calculated positions and re®ned riding on
their corresponding parent atoms. Geometrical parameters
were calculated by parst97.19 The plots of the molecules
were obtained by ortep3 included in the wingx suite.20 All
the calculations were carried out on the DEC Alpha 250
workstation at the Centro di Studio per la Strutturistica
Diffrattometrica of C.N.R., Parma. CCDC reference
numbers: 150943 (2a.CH3CN) and 150944 (2b.CH3CN).
This study con®rms that in apolar solvents CH3Y and
CH2XY guests show different binding modes, as previously
observed in the solid state. In particular the acidity of the
CH2XY guests strongly affects the binding ef®ciency
whereas modi®cation of this parameter with the former
guests gives the same association constants. With methylene
containing guests, the polarizability of the X and Y groups
strongly determines the binding process.
Acknowledgements
4. Experimental
4.1. NMR binding studies
This work was partly supported by Ministero dell'Univer-
Á
sita e Ricerca Scienti®ca (MURST) `Supramolecular
Devices' project. We are grateful to C.I.M. (Centro Inter-
dipartimentale di Misure `G. Casnati') for NMR and mass
measurements.
Binding studies were carried out in CDCl3 and/or CCl4 solu-
1
tion using H NMR spectroscopy (T300 K; [H0]0.01 M
and [G0]0.1 M). In all titration experiments an up®eld
Complexation Induced Shift (CIS) was observed for
the guests signal and the H NMR spectra showed time-
1
References
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È
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A
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0.2£0.3£0.4 mm suitable for the X-ray analysis was
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Ê
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Á
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