The use of 1H_I3C NMR correlations and its corresponding I1JCH has found a tremendous use in structural elucidation of organic compounds. Chapter 1 highlights different methods for determination of IH_13C correlations and for the measurement of I1JCH. In this work we reported two improved methods for determination of IH_I3C correlations (CTgc2HMBC) and, for the measurement of nJCH (SelEXSIDE). Chapter 2 describes the work undeliaken in order to quantify improvements to the gradient heteronuclear multiple bond correlation (HMBC) experiment specifically to design a constant time gradient HMBC (CTgc2HMBC) with adiabatic pulses. This was done in order to remove IH_IH modulation during fl , which causes cross-peak broadening, to simultaneously maximise sensitivity and resolution and then compare their performance against comparable non-constant time experiments. CTgc2HMBC experiment has shown slightly narrower cross peaks in the FI dimension which is maximised at high FI resolution especially 20 Hz/pt, compared to analogous gc2HMBC which is limited by IH-IH modulation. The CTgc2HMBC has been shown to be more efficient for weak IH_ 13C correlations. Chapter 3 describes the improvement made to the slow, easy to use EXSIDE sequence. The EXSIDE sequence was made to be doubly-selective in both the FI (I3C) and F2 (IH) domains. The modification, named Sel-EXSIDE reduces the number of tl datapoints used by reducing the FI spectrum width substantially, and thus reducing a multi-hour (7 hours 30 minutes 0 f experiment time to 0 btain 3 -7 co up ling co nstants) experiment to a matter of minutes (less than 10 minutes to obtain one coupling constant) while still allowing nJCH coupling constants to be resolved to -I Hz/pt resolution. The SelEXSIDE pulse sequence has been shown to work for determination of all measurable nJCH for both small (2-ethylI- indanone) and large (strychnine) organic molecules. Coupling constants obtained using SelEXSIDE, gave low mean errors and standard deviations when compared to other methods like Line-fitting procedures and calculated values using DFT.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:680109 |
| Date | January 2014 |
| Creators | Tatolo, Godiraone |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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