th  - 1988 - 51st ENC Conference

A PROBE WITH HIGHER DECOUPLING EFFICIENCY AND
F SENSITIVITY FOR SOLID STATE NMR EXPERIMENTS
84 I
Yi Jin Jiang * Warner R. Woolfenden Mark H. Sherwood Don W. Alderman
Ronald d. Pugmire, and David M. Grant, Departments of Chemistry and Fuels
Engineering, University of Utah, Salt Lake City, Utah 84112
A more efficient double-tuned 13C/1H probe circuit has been developed espe-
cially for higher decoupllng efficiency and improved sensitivity of the observa-
tion channel (13C).
Comparing this with the circuit in our previous paper (1), this modification
of the circuit of the circuit not only eliminates an expensive capacitor, but
also extends the space inside the probe, which lessens the arcing problem.
Because the capacitor C4 has been replaced by a relatively small stray
capacitance, the inductance L1 can be increased, resulting in a more efficient
decoupling power in the sample coil.
In a solid state NMR probe, for use at high frequencies (1H at 200 MHz or
above) a small coil is often required, and hence the inductance of the coil is
small. This decreases the sensitivity of the 13C channel. This problem can be
alleviated by replacing the single X/4 coaxial cable in the original circuit (1)
with three M4 cables in parallel, decreasing the inductance from ooint B to
ground, and increasing the sensitivity of the sample coil of the 13C channel.
(1) Yi Jin diang, Ronald d. Pugmire and David M. Grant, d. Magn. Reson. 71,
485 (1987).
COMPUTER PATTERN MATCHING IN 2D INADEQUATE SPECTRA
85 I
I
Janet Curtis", Charles L. Mayne, Don W. Alderman, Ronald J. Pugmire ÷ and David M. Grant
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112
+ Deparmaent of Fuels Engineering, University of Utah
An automated system for extraction of 13C-13C connectivites as deteci~ by the phase-sensitive, 2D
INADEQUATE NMR experiment is being developed. The cormectivites are contained in characteristic AX or AB
patterns consisting of pairs of plus-minus doublets in the 2D data set which have equal double quantum
frequencies, vl:X~. The software accepts a line list from a quantitative 1D 13C spectrum, sons the lines by intensity,
and selects pairs with commensurate intensities to establish subsets of the full data set to be searched for a possible
carbon-carbon bond. The program uses a simplex algorithm to perform non-linear surface-fitting for each coupled
pair of spins. The adjustable parameters are intensities of the doublets, 1Jcc, the chemical shifts, and the T 2
relaxation parameters. The double quantum frequency is simply the algebraic sum of the chemical shifts. For each
statistically significant pattern obtained, a bond is assigned between the two coupled carbon nuclei. The antiphase
doublets are a pattern more easily recognized in spectra with low S/N and the computer algorithm takes advantage
of this additional information.
The simulation routines will be described. The pattern matching software has been tested for spectra with up
to 11 shifts and 10 couplings . . . .
The objective of the research is the extraction of maximum information from the 2D INADEQUATE spectra
in complex mixtures such as fossil fuels and in large natural product molecules, etc.
141