Studies in nitrosopyrazoles. Part 2.1 Solution and solid-state NMR studies of 3,5-disubstituted and 1,3,5-trisubstituted-4-nitrosopyrazoles. Crystal structures of 1,3,5-trimethyl-4-nitrosopyrazole and 3,5-di-tert-butyl-4-nitrosopyrazole
作者:Daniel A. Fletcher、Brian G. Gowenlock、Keith G. Orrell、Vladimir Šik、David E. Hibbs、Michael B. Hursthouse、K. M. Abdul Malik
DOI:10.1039/a607063i
日期:——
Variable temperature NMR studies of a range of 3,5-disubstituted
(R = R′ = Me,
But) and 1,3,5-trisubstituted (R, R′,
R″ = Me, CF3, Ph or
Bui)-4-nitrosopyrazoles have led to the identification of
individual rotational isomers at low solution temperatures arising from
the slowing down of the rotation of the nitroso function with respect to
the pyrazole ring. Rotational energy barriers
[ΔG‡ (298.15 K)],
calculated by total NMR bandshape analysis, were in the range
38–65 kJ mol-1. The –NO
rotation process also occurs in the solid state and leads to disorder in
the crystal structures of 1,3,5-trimethyl-4-nitrosopyrazole and
3,5-di-tert-butyl-4-nitrosopyrazole. The
1-H-3,5-disubstituted-4-nitrosopyrazoles exhibit rapid
annular tautomerism in solution.
对一系列3,5-二取代(R = R′ = Me、But)和1,3,5-三取代(R、R′、R″ = Me、CF3、Ph或Bui)-4-亚硝基吡唑进行可变温度核磁共振研究,从而确定了在低溶液温度下,由于亚硝基功能相对于吡唑环的旋转减慢而产生的单个旋转异构体。通过总核磁共振波谱分析计算的旋转能垒[ΔG‡ (298.15 K)]在38-65 kJ mol-1范围内。–NO旋转过程也发生在固态下,并导致1,3,5-三甲基-4-亚硝基吡唑和3,5-二叔丁基-4-亚硝基吡唑的晶体结构混乱。1-H-3,5-二取代-4-亚硝基吡唑在溶液中表现出快速的环状互变异构。