首页> 外文期刊>The Journal of Organic Chemistry >Near-Silence of Isothiocyanate Carbon in C-13 NMR Spectra: A Case Study of Allyl Isothiocyanate
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Near-Silence of Isothiocyanate Carbon in C-13 NMR Spectra: A Case Study of Allyl Isothiocyanate

机译:C-13 NMR光谱中的异硫氰酸酯碳的几乎沉默:一个异硫氰酸烯丙酯的案例研究

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摘要

H-1 and C-13 NMR spectra of allyl isothiocyanate (AITC) were measured, and the exchange dynamics were studied to explain the near-silence of the ITC carbon in C-13 NMR spectra. The dihedral angles alpha = angle(C1-C2-C3-N4) and beta = angle(C2-C3-N4-C5) describe the conformational dynamics (conformation change), and the bond angles gamma = angle(C3-N4-C5) and epsilon = angle(N4-C5-S6) dominate the molecular dynamics (conformer flexibility). The conformation space of AITC contains three minima, C-s-M1 and enantiomers M2 and M2'; the exchange between conformers is very fast, and conformational effects on C-13 chemical shifts are small (nu(M1) - nu(M2) < 3 ppm). Isotropic chemical shifts, ICS(gamma), were determined for sp, sp(x), and sp(2) N-hybridization, and the gamma dependencies of delta(N4) and delta(C5) are very large (10-33 ppm). Atom-centered density matrix propagation trajectories show that every conformer can access a large region of the potential energy surface AITC(gamma,epsilon,...) with 120 degrees < gamma < 180 degrees and 155 degrees < epsilon < 180 degrees. Because the extreme broadening of the C-13 NMR signal of the ITC carbon is caused by the structural flexibility of every conformer of AITC, the analysis provides a general explanation for the near-silence of the ITC carbon in C-13 NMR spectra of organic isothiocyanates.
机译:测量了异硫氰酸烯丙酯(AITC)的H-1和C-13 NMR光谱,并研究了交换动力学以解释C-13 NMR光谱中ITC碳的近沉默。二面角α=角度(C1-C2-C3-N4)和β=角度(C2-C3-N4-C5)描述了构象动力学(构象变化),键角γ=角(C3-N4-C5) )和ε=角度(N4-C5-S6)决定了分子动力学(顺应性柔性)。 AITC的构象空间包含三个最小值C-s-M1和对映异构体M2和M2';构象体之间的交换非常快,并且构象对C-13化学位移的影响很小(nu(M1)-nu(M2)<3 ppm)。确定了sp,sp(x)和sp(2)N杂化的各向同性化学位移ICS(γ),并且delta(N4)和delta(C5)的伽马依赖性非常大(10-33 ppm )。以原子为中心的密度矩阵传播轨迹表明,每个构象异构体都可以以120度

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