Gamma gauche effect

Selected and 13C solution-state (CDC13), and solid-state cp/mas 13C-NMR parameters for the quaternary ammonium salt are listed in Table 10. The termini of the benzo fragment were differentiated by the finding of a 6.8% intensity increase into 8 4.77 H(62) exo upon <5 8.12 H(7). The two A -methyl groups were differentiated by the observance of a 7.1% intensity increment into 8 4.16 H(3) axial upon <5 3.35 NC//3 axial. The lists of solid-state 13C chemical shifts of the two pseudopolymorphs are seen to be different (especially those for C(l)). The C(l)-0(2)-C(3)-C(4) dihedral angle was 135° and 78° in crystalline (reference,IS,3R)-TCC (33) and (retro-inverso,lS,3R)-BC (34), respectively. Thus, also in this case, the cp/mas chemical shifts of 8 84.34 (for 33) and 8 76.87 (for 34) can be easily rationalized in terms of a gamma-gauche effect. 

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