Microwave spectrum, molecular structure, barrier to internal rotation of methyl group, and ab initio MO calculation of 1-chloro-2-nitrosopropene, syn-ClCHC(CH3)–NO

Preparations ofC-Nitroso Compounds

“…[390][391][392][393][394] The bases used for dehydrohalogenation of the chlorooximes include triethylamine, 395 1,5-diaza-bicyclo[4,3,0]non-5-ene, 396 sodium alkoxides, 397 stirring a suspension of freshly ground sodium carbonate suspended in dry tert-butyl methyl ether 398 (or in diethyl ether 399 or methylene chloride 400 ), a two-phase system of aqueous sodium carbonate and methylene chloride, 401 stirring with sodium bicarbonate in alcohol, 402 and stirring with calcium hydroxide suspended in ethyl acetate containing 0.5% water. 403 For the synthesis of gaseous nitrosoalkenes, the chlorooxime is passed over sodium bicarbonate or potassium carbonate at room temperature, 392,394 although direct dehydrochlorination by pyrolysis at 450 °C is preferred. [390][391][392][393] Dehydrochlorination of chlorooximes by triethylamine in organic solvents such as benzene, 404 DMF, 395 or acetonitrile 405 results in rapid generation of nitrosoalkenes.…”

“…Others have been prepared in the gaseous state using flow techniques, and the identification of the short-lived nitrosoethenes has been accomplished by microwave spectroscopy. − The bases used for dehydrohalogenation of the chlorooximes include triethylamine, 1,5-diaza-bicyclo[4,3,0]non-5-ene, sodium alkoxides, stirring a suspension of freshly ground sodium carbonate suspended in dry tert- butyl methyl ether (or in diethyl ether or methylene chloride), a two-phase system of aqueous sodium carbonate and methylene chloride, stirring with sodium bicarbonate in alcohol, and stirring with calcium hydroxide suspended in ethyl acetate containing 0.5% water . For the synthesis of gaseous nitrosoalkenes, the chlorooxime is passed over sodium bicarbonate or potassium carbonate at room temperature, , although direct dehydrochlorination by pyrolysis at 450 °C is preferred. − Dehydrochlorination of chlorooximes by triethylamine in organic solvents such as benzene, DMF, or acetonitrile results in rapid generation of nitrosoalkenes. Dehydrochlorination of dimeric vicinal chloronitroso compounds by triethylamine has been employed by Pritzkow − for the preparation of a wide variety of β-nitrosostyrenes.…”

The microwave spectrum of methyl chlorodifluoroacetate: Methyl internal rotation and chlorine nuclear electric quadrupole coupling

“…We observe that for some molecular frames replacing a hydrogen with a chlorine increases the barrier to internal rotation, where as for other molecular frames replacing a hydrogen with a chlorine causes a decrease to the barrier. Arguments explaining this different behaviour have invoked steric factors [8]. An extreme case of barrier increase is seen for toluene [40] versus o-chlorotoluene [9,10], see Table 4.…”

“…However, only a few molecules of this type have been examined at a high enough resolution in which internal rotation fine structure and chlorine nuclear quadrupole splittings have been observed. Examples include acetyl chloride [3], 1-chloro-1-fluoroethane [4], 1-chloro-1, 1-difluoroethane [5], cis-chloropropene [6], cis-1-chloro-2-methylpropene [7], 1-chloro-2-nitrosopropene [8], and o-chlorotoluene [9,10]. A comparison of methyl group internal rotation barriers in mono-chlorinated species and non-chlorinated analogs shows that the presence of Cl can (i) increase the barrier to internal rotation when the Cl is close to the methyl rotor, but can also (ii) decrease the barrier to internal rotation when the Cl is far away from the methyl rotor.…”