CHBrCOOR fragments of bromine-containing mono-and dicarboxylates show 13C NMR signals in the range 38-45 ppm, at 12-15 ppm to high field of their chloro analogues. The introduction of one bromine atom into the a-CH, group causes a 6-13 ppm shift of the carbon signal, depending on the type of ester. The replacement of H with Br in '3CH,(COOR), has only a negligible influence on the l3CH, signal position. The CBr,COOR fragment signals appear in the range 50-54 ppm. 13C NMR data, including the chemical shift values, signal multiplicities and spin-spin couplings, make possible the identification of isomers present in isomer mixtures of bromine-containing esters. The '"COOR chemical shifts of diastereomers of a,& dibromoesters differ noticeably from each other, and the 13CNMR spectra can thus be used to supply preliminary information about the stereochemistry of bromine addition to @-unsaturated acids.
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INTRODUmIONIn view of the complex nature of interactions between the bromine atoms and other structural fragments in bromine-containing organic compounds' which manifests itself in the 13CNMR spectra of brominated methanes and ethanes,' the collection of more experimental data on the 13CNMR spectra of organobromine compounds is needed both for the purposes of diverse chemical applications and for the determination of useful correlations. Relatively few s t~d i e s~-~ on the 13CNMR spectra of esters have been published; in some cases, erroneous assignments have been made.' Hardly any 13C NMR spectra of brominecontaining esters of saturated acids have been reported.
EXPERIMENTAL CompoundsThe compounds studied (Tables 1-4) were prepared according to known procedures; their purity was checked by GLC. Compounds 3, 5, 11 and 13 were made by bromination of the acids in the presence of red phosphorus, followed by treatment of the reaction mixtures with methanol according to Refs 8 and 9.Compounds 10, 12, 17 and 27 were synthesized by a typical procedure,'" viz. addition of bromine to the corresponding unsaturated compounds in glacial CH,COOH at room temperature. Compounds 15 and 20 were obtained by telomerization of C,H, with 5." Esters 22-25 were made by halogenation of 21.12 Adduct 16 was prepared by the addition of CC1,Br' to CH,=CHCOOCH3.13 Methyl tribromoacetate (7) was obtained by esterification of CBr,COOH with * Author to whom correspondence should be addressed Tables 1-4 were commercial products, purified by distillation or preparative GLC.
NMR procedureThe 13C---IH and 13C-{'H} spectra were measured on a Bruker HX-90 spectrometer as described ear-]ier.'4.'5 The samples were 9 : l compound/chloroform mixtures. Chloroform was used as internal reference (77.17 ppm from TMS) unless otherwise stated. The standard measurement error was 0.1 ppm for chemical shifts and 1 Hz for the spin-spin coupling constants.
RESULTSThe I3C NMR data of esters of brominated mono-and dicarboxylic acids are discussed in this paper. As in the case of alkyl halides,, both bromine and chlorine shift the signal of the adjacent carbon atom ...
