Carbonates, Thiocarbonates, and the Corresponding Monoalkyl Derivatives. 1. Their Preparation and Isotropic ¹³C NMR Chemical Shifts

Abstract

Three series of potassium carbonate and thiocarbonate salts were synthesized, and the corresponding (13)C isotropic solid-state NMR and the aqueous solution (13)C and (1)H NMR data were collected. The series of compounds that were studied consists of (1) the parent compounds, i.e., potassium carbonate, K(2)CO(3), potassium hydrogen carbonate, KHCO(3), potassium monothiocarbonate, K(2)CO(2)S, potassium dithiocarbonate, K(2)COS(2), and potassium trithiocarbonate, K(2)CS(3), (2) the oxygen monoalkyl substituted derivatives of the parent compounds (OR series), i.e., three potassium O-alkylcarbonates, KO(2)COR, three potassium O-alkylmonothiocarbonates, KOSCOR, and three potassium O-alkyldithiocarbonates, KS(2)COR, all with R = CH(3), CH(2)CH(3), CH(CH(3))(2), and (3) the sulfur monoalkyl substituted derivatives of the parent compounds (SR series), i.e., two potassium S-alkylmonothiocarbonates, KO(2)CSR; two potassium S-alkyldithiocarbonates, KOSCSR, and two potassium S-alkyltrithiocarbonates, KS(2)CSR, all with R = CH(3) or CH(2)CH(3). The preparation and proper characterization of KO(2)CSR and KOSCSR with R = CH(3) and CH(2)CH(3) along with new IR and X-ray powder diffraction data for several other compounds in the series are reported for the first time in this study. Solution NMR data for KO(2)CSR (R = CH(3), CH(2)CH(3)) and KOSCSR (R = CH(3)) and solid-state NMR data for K(2)CO(2)S and K(2)COS(2) could not be obtained because they are unstable under the corresponding measurement conditions. The isotropic chemical shift values of the central carbon atoms obtained from solid-state MAS (magic angle spinning) NMR experiments deviate at most by 3 ppm from the corresponding solution values. Two major trends in the (13)C chemical shift values of the central carbon atoms were found. First, if an oxygen atom in a parent compound or in an alkyl-substituted derivative is replaced by a sulfur atom, a significantly higher chemical shift value is observed. This trend is discussed in terms of the paramagnetic contribution to the chemical shielding constant. Second, the size of the alkyl group in the monoalkyl derivatives has a very small effect on the chemical shift values of the central carbon atoms. This observation is explained using the concept of varying inductive effects produced by alkyl groups. The trends observed for the (13)C and (1)H chemical shift values of the alkyl groups follow common concepts on the structure dependency of chemical shifts.

Carbonates, Thiocarbonates, and the Corresponding Monoalkyl Derivatives: III. The 13C Chemical Shift Tensors in Potassium Carbonate, Bicarbonate and Related Monomethyl Derivatives

“…The 13 C isotropic solution and solid-state chemical shift values in ionic potassium carbonates and thiocarbonates were previously measured and interpreted in our laboratory [1]. The present paper reports the 13 ), measured on powdered samples in solid-state nuclear magnetic resonance (NMR) experiments.…”

“…The resolution of the corresponding 13 C CHEMICAL SHIFT TENSORS IN POTASSIUM CARBONATE three magnetically non-equivalent central carbons and of two of the methyl carbon atoms in a solid-state CPMAS NMR experiment was reported from our laboratory [1]. In this work, the principal values for each of the central carbon and for the two resolvable methyl carbon atoms were measured in a 2-D PHORMAT [12] experiment and the values are reported.…”

“…Both compounds were used without further purification. All the other compounds were synthesized, following the experimental procedures described previously [1].…”

“…While there are limited data available on sulfur substituent effects, this smaller effect is consistent with the fact that the shift in the perpendicular component is 15 ppm in CH 3 SH versus 70 ppm in CH 3 OH. The values of the two inplane components for CS 2À 3 are approximately 180 ppm larger than for CO 2À 3 , indicating a significant increase in the paramagnetic contribution [1,44]. This can be rationalized by the decrease in the energy separation between the HOMOs and LUMOs of the anions when the oxygen atoms are substituted with sulfur atoms [1,45].…”

A diverse structural behaviour of boronated ortho-phthalaldehydes: A crystal structure of 1,3-dihydro-1,3-dihydroxy-4-formylbenzo[c][2,1]oxaborole

“…The 13 C NMR chemical shifts for samples dissolved in K 2 CO 3 /D 2 O were calibrated using the value of 168.3 ppm referenced for K 2 CO 3 [23]. …”