The structure of the methyloxocarbonium ion was investigated in three salts: SbCI; CHACO +, AICIg-CHACO + and GaCI~-CHACO + by X-ray crystallography. Three dimensional X-ray data were collected on a diffractometer (Mo K~ radiation). The structures were solved by Patterson methods and refined by full-matrix least-squares analysis. The crystal structures provide direct proof of an ionic structure in the solid state. In each salt the methyloxocarbonium ion is linear and no association of the oxocarbonium ion with the anions other than ionic crystal packing is observed in accordance with the infrared spectrum.
-38, b--12.60, c= 19.42 A; the space group is Pbca. The structure was determined by using 1797 independent reflexions collected on a linear diffractometer using Mo K~ radiation. The crystal structure, including hydrogen atoms, was refined by tile full-matrix least-squares method to an unweighted RI value of 0.044 and a weighted R2 value of 0.050. This salt consists of discrete hexachloroantimonate anions and o-methyl-phenyloxocarbonium cations. The closest interionic contacts are found between the carbonyl carbon of the [o-CH3.C6H4CO] + cations and the chlorine atoms of the [SbCl6]-anions. The C-O bond length of 1.Ill (13) A is similar to that determined in alkyioxocarbonium ions, but the adjacent C-C bond length of 1.387 (14) A, is significantly shorter than that found in alkyloxocarbonium ions. On the other hand, the positive charge of the [o-CH3. C6H4CO] + cation is largely delocalized into the phenyl ring whereas this charge is localized on the carbonyl carbon in alkyloxocarbonium ions.
Propionyl chloride forms with aluminum chloride a molecular addition compound A1C13. CH3CH2COCI. The crystals are monoclinic, space group P21/c, with unit-cell dimensions a=6.581, b=19.106, e= 8.711 A and fl= 120.4 °. Three-dimensional X-ray data were collected on a linear diffractometer (Mo K~ radiation). The crystal structure was refined by full-matrix least-squares analysis to a reliability index R = 0.043 for 731 observed reflexions. The adduct is composed of an AICI3 group coordinated with the oxygen of the propionyl chloride. The structure is built up from discrete AIC13. CH3CH2COCI molecules.
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