engleski

Studies of monomer-dimer equilibrium of 2-nitrosopyridines in solution and in solid state

On contrary to nitrosobenzenes which appear in solution at room temperature exclusively as monomers, the preferred forms of 2-nitrosopyridines are Z-dimers. In addition, whereas nitrosobenzenes are mostly present as E-dimers in solid state, 2-nitrosopyridines are Z-stereomers. In the present work we studied monomer-dimer equilibrium of 2-nitrosopyridine (1) and its 4-methyl- (2) and 4-chloro- (3) derivatives (Scheme 1) both in solution and in solid state. Thermodynamic data for the dissociation of compounds 1-3 acquired by UV/VIS spectroscopy indicate that Z-dimers are thermodynamically favored over monomers at room temperature in solution. Furthermore, by using variable temperature 1H NMR spectroscopy we showed that compound 1 is able to form mixed dimers with p-nitronitrosobenzene. Solid-state photochemical studies of Z-configured 2-nitrosopyridine derivatives 1-3 by IR spectroscopy at cryogenic conditions indicate that all three compounds undergo photodissociation to corresponding monomers. The process is reverted by warming the samples to room temperature. Photolytic dissociation of compounds 1-3 enabled complete assignment of IR spectra of the resulting monomers for the first time. Experimental IR spectra of monomers of compounds 1-3 are in good agreement with the calculated spectra.

2-nitrosopyridine ; solid-state ; photochemistry

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