th  - 1988 - 51st ENC Conference

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INTERPRETAT IION OF 13 C NHR MIXTURE SPECTRA BY MULTIVARIATE ANALYSIS:
Trond Brekke, 01av M. Kvalheim and Einar Sletten
Dep. of Chemistry, Univ. of Bergen 5007 Bergen, Norway
High-resolution 13C NMR spectroscopy oT complex mixtures, e.g fossil hydro-
carbons, provides large amounts of data. The interpretation and quanti-
fication of such spectra require the use of multivariate data analysis.
Principal Component (PC) analysis of 13C spectra of 12-component synthetic
hydrocarbon mixtures £nd£cates that more than 98Z of the variat£on in the
spectra is due to chemical variation among the Samples and an efficient
means of reveaZing correZations among resonances (e.g. subspectra of single
components) is presented. Partial-Least-Squares (PLS) regression is used to
establish models for the prediction of densitY, mean molecular weight and
refractive index of the samples from the spectra.
2oi I
THE CORRELATION OF IH-lmF COUPLINGS BY HETERONUCLEAR BODE _PULSED DECOUPLING
(HUltPD)
Stephen H. Grode and Russell W. Gillis, The Upjohn Co., Fine Chemicals,
Kalamazoo, HI 49071
The identification and characterization of fluorinated compounds is complicated
by the ubiquitous nature of the 1H-19F scalar interaction. This is
particularly true of fluorinated steroids in which the observation of 5 bond
1H-19F couplings is not unusual. The typical method used to identify IH-19F
coupling is to apply a CW signal to each proton of interest and observe its
effect on the 19F resonance. This is unsatisfactory for three reasons: I) The
small long range couplings often go unobserved, 2) In a crowded spectrum it is
difficult to irradiate a single proton without affecting neighboring protons,
and 3) If a number of protons need to be irradiated the experiment is time
consuming. These problems can be alleviated by performing the experiment in
the opposite configuration (i.e. 19F decouple IH observe in place of 1H
decouple 19F observe). A HeteronUclear Bode -pulsed Decoupling (HUMPD) method
was developed to acquire 19F spin decoupled 1H-NMR spectra. This is a gated
decoupling method in which 19F transmitter is triggered to pulse between
sampling times. The purchase of a heteronuclear decoupler is not required.
This method is demonstrated in the ID and 2D (HUMPD-COSY) realms by application
to fluocinolone acetonide. In the 2D experiment, HUMPD is applied during
acquisition, thus collapsing the IH-IgF interaction during the T2 time domain
only. This yields a 2D spectrum in which it is possible to observe all the
IH-IH couplings, as in a normal COSY, and identify the fluorine interacting
protons by virtue of a crosspeak collapse along F2.
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