Accounting for intermolecular effects in the calculation of 15N NMR chemical shifts of protonated nitrogen-containing compounds

Russian Journal of Organic Chemistry -     

N-(2,2-Dichloro-2-phenylethylidene)arenesulfonamides in reactions with secondary amines

N-(2,2-Dichloro-2-phenylethylidene)arenesulfonamides were synthesized by a modified procedure, and their reactions with secondary amines were studied for the first time. Reactions of imines with dialkylamines proceed at room temperature to afford α,α-dichloromethylbenzene and N,N-dialkyl-N′-(arenesulfonyl)formamidines arising from the haloform cleavage of the initially formed unstable N-(1-dialkylamino-2,2-dichloro-2-phenylethyl)arenesulfonamides. When the reaction is carried out upon cooling to 0°C, the products of the nucleophilic addition of secondary amines to azomethines, N-(1-dialkylamino-2,2-dichloro-2-phenylethyl) are formed in yields of no higher than 5%. Nonempirical calculations of ¹³C-¹H spin-spin coupling constants and their experimental measurements for the series of the synthesized N-arenesulfonamides were performed to show that these compounds exist in solutions exclusively as E isomers. Preferable conformations of the investigated compounds and the relative energies of their E and Z isomers in the gas phase were determined by quantum-chemical calculations at the MP2/6-311G** level of theory. The NMR spectral data revealed restricted rotation of the N,N-dialkylamino group about the partially double C-NAlk₂ bond in the molecules of N-arenesulfonylformamidines.     

<Superscript>13</Superscript>C-<Superscript>13</Superscript>C spin-spin coupling constants in structural studies: XLIV. Carbonyl-containing oximes

¹³C-¹³C spin-spin coupling constants in carbonyl-containing oximes were calculated in terms of the second-order polarization propagator approximation (SOPPA) with account taken of the results of theoretical conformational analysis. Stable conformations of all carbonyl-containing oximes were found to have s-trans orientation of the carbonyl group in the E and Z isomers. The corresponding ¹³C-¹³C coupling constants showed a characteristic dependence upon internal rotation of the carbonyl-containing substituent, which may be used to determine predominant rotational conformations of these compounds. A relation between orientation of the C=O bond and ¹³C-¹³C coupling constants for the adjacent bonds in oximes was revealed; it may be attributed to hyperconjugation between the corresponding carbon-carbon bond and antibonding orbital of the C=O bond.