th - 1987 - 51st ENC Conference
th - 1987 - 51st ENC Conference
th - 1987 - 51st ENC Conference
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MF53 - POSTERS<br />
DI-13C-LABELING: A MEANS TO MEASURE 12C-13C<br />
ISOTOPIC EQUILIBRIA IN 2-NORBORNYL CATION.<br />
Ronald M. Jarret*, Department of Chemistry, College of <strong>th</strong>e<br />
Holy Cross, Worcester, MA 01610.<br />
Martin Saunders, Department of Chemistry, Yale University,<br />
New Haven, CT 06511.<br />
2,3-Di-13C-norborn-2-yl chloride was prepared and<br />
ionized (wi<strong>th</strong> SbF 5) to 2-norbornyl cation. In solution<br />
at -65°C, rapid rearrangements occur which completely<br />
scramble <strong>th</strong>e 13C-labels. The proton-decoupled cmr<br />
spectrum (62.7 MHz) contains <strong>th</strong>ree signals: C-4, C-I,2,6<br />
(averaged), and C-3,5,7 (averaged). The 13C-labels are<br />
<strong>th</strong>us equilibrated over non-equivalent sites wi<strong>th</strong>in<br />
2-norbornyl cation. This 12C-13C equilibrium isotope<br />
effect alters <strong>th</strong>e proportion of di-13C-labeled isomers<br />
from statistical values. The non-statistical isotopic<br />
isomer population is manifested as an asymmetric<br />
multiplet for <strong>th</strong>e averaged C-3,5,7 peak in <strong>th</strong>e cmr<br />
spectrum. The relatively sharp lines of <strong>th</strong>e multiplet<br />
can be reproduced wi<strong>th</strong>in ± 0.i ppm, wi<strong>th</strong> isotopic<br />
equilibrium constants of K-3,5,7 = 1.010 t 0.005 and<br />
K-I,2,6 = 1.039 t 0.005.<br />
71<br />
6<br />
4 8<br />
CI(H)<br />
H(CI)
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