6. Result

The figure shows an expansion of the aliphatic region of the 1,1-ADEQUATE spec- trum obtained on a DRX-600 spectrometer using a multinuclear inverse z-gradient probe-head. We start the interpretation of the figure at the left-hand side. Proton H-12 has its signal at 5; = 4.28; two correlation signals at the double-quantum frequencies & = 119.3 and 125.1 can be seen. This corresponds to dc-12 = 76.85 + d¢.1; = 42.48 and &-12 = 76.85 + &.13 = 48.22 and confirms the binding situation for C-12. The protons H-23 (64 = 4.0 to 4.2) are situated on a carbon with only one carbon atom neighbor. Therefore their correlation signals are found at d¢.23 = 64.60 + dy = 127.34 giving 191.9. Going to the right-hand site of the figure, we find H-13 at 6; = 1.27. C-13 at & = 48.22 is connected to three other carbon atoms, C-8, C-12 and C- 14. Therefore we find the three correlation signals at the corresponding double-quantum frequencies 108.2, 125.1 (as seen before in the signal of H-12) and 79.8. Similarly all the other correlation signals can be assigned using the table of chemical shift data for strychnine in the appendix.

7. Comments

In section a of the sequence we find an INEPT transfer from protons to ¹³C. The antiphase ¹³C magnetization 2/ H, Icy present after p12 develops C,C spin coupling to a second ¹³C nucleus yielding a term4/y, Ic, Ic, - This is transformed into double- quantum coherence by p14 at the end of section b. In section ¢ the double-quantum chemical shifts of ¹³C develop during t,. Section d has three purposes. The double-quantum ¹³C coherences have to be reconverted to single-quantum coherences, which is achieved by a 60° pulse p16, giving a higher efficiency for this process than in Experiment 12.16. The gradient g1 dephases signals that are in the double-quantum state and gradient g2 further dephases the ¹³C coherences after reconversion into proton-¹³C antiphase magnetization. Finally the situation must be prepared for the back transfer to protons, which is achieved by the refocusing period [g2, d5, p17, 3]. The back transfer (section e) is performed in section e with sensitivity enhancement using the PEP principle as already described in Experiment 12.8. Note that both '(C,H) and 'J(C,C) vary widely in organic compounds and the success of the experi- ment relies on reasonably well-chosen values. According to Reference [4] it is very advisable to use adiabatic 180° pulses for this sequence.

8. Own Observations