¹³C and ⁷⁷Se NMR of some selenium and thiophene derivatives. ¹J, ²J and ³J SeSe coupling constants

Abstract

The results of 13C and (when pertinent) 77Se NMR spectra of thiophene and selenophene derivatives containing exocyclic selenium atoms are presented. The "Se spectra show an interaction between nitro or carbonyl groups and selenium when they are ortho to each other. The measurement of 'J(SeSe), 'J(SeSe) and 3J(SeSe) has been attempted on disymmetric diselenides; only 'J(SeSe) can be measured and values are very low, generally below 20 Hz. Other couplings cannot be observed and are smaller than the line width, which is 2 Hz. No theoretical interpretations can be advanced at present.The 13C and 77Se NMR of organic selenium and thiophene derivatives is becoming increasingly well especially in the selenophenic series. The 13C and 77Se NMR spectra of some new compounds are presented in this paper, including the selenium-selenium coupling constants. EXPERIMENTALThe NMR spectra were obtained on a Bruker W H 9 0 C and both 13C and 77Se were observed in the Fourier transform mode using a multi-nuclear probe.The 13C spectra were measured at 22.63MHz with a pulse width of 9 ps (90" pulse = 14 ps), a waiting time of 1 s between each scan and an exponential filtering of 3Hz. The sweep width was 6000Hz and the decay was stored in 4 K data points. The solvent, either deuterochloroform or acetone-d6, was used as * Author to whom correspondence should be addressed internal reference using i313c = 76.91 ppm for CDCl, and 6 1 3~ = 29.22 ppm for a~etone-d,.'~ Cr"' (acac), was used to observe the quaternary carbons; in this case there was no waiting time between each scan. No effects were observed on the chemical shifts which were measured with an error of kO.1 ppm.The 77Se spectra were observed at 17.19 MHz with the same solvent and lock as for I3C. The pulse width was 10 p s (90" pulse = 18.5 ps) and a waiting time of 2 s was used between each scan. The sweep widths were different according to the observed chemical shift, but 4 K data points were always used. The resonance frequencies were measured for each sample and compared to a reference sample of Se(CH,), in CDC1,. When the lock was deuteroacetone the appropriate correction was applied. The temperature was 26°C. According to the reference procedure, the chemical shifts are given with an estimated error of *0.5 ppm. J(77Se77Se) values were measured using a reduced sweep width of approximately 2000Hz and 8 K data points; 1000-30000 scans were stored. The error is ztO.5 Hz for the measurable values. The upper limits of the J values for the smaller coupling constants are given by the width at the base of the main line.Some of the compounds studied were prepared according to literature methods: 1,16 2,17 13,18 3,19 5,29 8, 11 and 12," 15 and 17.,' Compound 4, first prepared by Challenger et al.," was obtained by the action of sulphur and ethyl bromoacetate on 3-lithiothiophene.14 was obtained by a procedure similar to that used for 13. The bromide derivative was prepared from 2-nitro-3-thienyl selenocyanate in chloroform and an equimolar solution of phenylselenol in chloroform adde...

Carbon-13 nuclear magnetic resonance studies of organotellurium compounds. II. Chemical shift trends

“…However, the available data on tellurium which corresponds to a decrease in the tellurium compounds are limited compared with polarity of the Te-C bond. ~a g n e t i c anisotropic those for sulphur and selenium (5)(6)(7)(8)(9)(10)(11)(12)(13)(14). effects originating in the tellurium substituents are we have recently reported our studies on 1 3~ nmr not expected to vary much in this closely related spectra of phenyl and p-methoxyphenyl tellurium series; moreover, they are expected to be small (8).…”