th  - 1987 - 51st ENC Conference

!
1.7
MF51
ULTRA-HIGH RESOLUTION IN IH SPECTRA AT $00 MHZ:
CHLORINE ISOTOPE EFFECTS
Frank A. L. Anet and Max Kopelevich*
Department of Chemistry and Biochemistry
University of California, Los Angeles
Los Angeles, CA 90024
We have observed chlorine isotope effects on the IH nuclear shielding in chloroform
and methylene chloride. These effects are on the order of 0.2 ppb and are readily detectable
at high fields (11.4"13 provided some care is taken in sample preparation and in optimizing
field homogenuity. Application of Lorentzian-Gaussian resolution enhancement allows
baseline separation of the resonance lines with areas corresponding to statistical weights of
the various C135/C137 isotopic combinations, as shown below. This appears to be the first
example of chlorine isotope effects on IH shifts.
We are currently undertaking studies of isotope effects in other halogenated
methanes, exploring the solvent dependence of these effects, as well as looking into different
means of obtaining ultra-high resolution spectra.
' '5 ' ' ' ' '0 ' , , i
HERTZ
500 MHz IH{D} spectrum of 2% CHDCI 2 in CD2CI 2. Ratios of the areas are approximately
9:6:1.