Relative carbonyl isocyanate cation [OCNCO]+ affinities of pyridines determined by the kinetic method using multiple‐stage (MS3) mass spectrometry
Relative carbonyl isocyanate cation [OCNCO]+ affinities of pyridines determined by the kinetic method using multiple‐stage (MS3) mass spectrometry
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使用多级 (MS3) 质谱法通过动力学方法测定吡啶的相对羰基异氰酸酯阳离子 [OCNCO]+ 亲和力
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
M. Eberlin
中科院分区：
文献类型：
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作者：
S. Yang;Guodong Chen;Shuguang Ma;R. Cooks;F. Gozzo;M. Eberlin
五重四极质谱仪中的离子-分子反应用于产生团簇离子，其中中性吡啶分子与线性多原子阳离子[OCNCO]+结合。二聚体加合物，即Py 1 [OCNCO]+ Py 2，其中Py 1和Py 2代表取代的吡啶，在质量选择的[OCNCO]+与吡啶混合物反应后形成，具有松散结合的结构，如三级质谱（MS 3）实验所示。由Meta位和/或对位取代的吡啶组成的二聚体加合物（未受阻吡啶）显示出碎片离子丰度比ln [Py 1 [OCNCO]+/Py 2 [OCNCO]+]与吡啶的质子亲和力差异之间的极好的线性相关性。在假定[OCNCO]+结合的二聚体的有效温度与相应的Cl+结合的二聚体的有效温度相似的情况下，估计取代吡啶相对于吡啶的[OCNCO]+亲和力为3-MePy 2.3，4-MePy 3.2，3-EtPy 3.5，4-EtPy 4.1，3，5-diMePy 4.9和3，4-diMePy 5.6 kcal mol−1（1 kcal = 4.184 kJ）。使用假定的有效温度555 K，推导出相对[OCNCO]+阳离子亲和力和相对质子亲和力（PA）之间的线性关系为相对[OCNCO]+亲和力（kcal mol−1）= 0.96 ΔPA。邻位取代的吡啶组成的二聚体显示邻位取代的烷基基团和中心[OCNCO]+阳离子之间的大量空间效应。测定了一组气相空间参数（Sk），空间效应的顺序为2-MePy（-1.39）<2，5-diMePy（-3.02）<2，4-diMePy（-3.15）<2，3-diMePy（-3.29）<2，6-diMePy（-5.09）<2，4，6-triMe（-6.13）。由于Py[OCNCO]+ Py中的中心离子较大，[OCNCO]+ Py体系中的空间位阻效应比相应的Cl+体系中的空间位阻效应大。通过从头计算得到了[OCNCO]+、Py[OCNCO]+和Py[OCNCO]Py+的键角、键长和电荷密度分布等结构和电子信息。计算表明，[OCNCO]+与碳原子上的高正电荷密度呈线性关系。计算还表明，Py[OCNCO]+单体是一个平面离子与吡啶的氮原子结合的[OCNCO]+阳离子的碳原子，和Py[OCNCO]Py+二聚体是一个对称的离子，其中吡啶分子上的氮原子结合的中心簇离子，[OCNCO]+的碳原子。
Ion-molecule reactions in a pentaquadrupole mass spectrometer are used to generate cluster ions in which neutral pyridine molecules are bound to a linear polyatomic cation, [OCNCO]+. The dimeric adduct, viz. Py1[OCNCO]+Py2 where Py1 and Py2 represent substituted pyridines, formed upon reaction of mass-selected [OCNCO]+ with a mixture of pyridines, has a loosely bound structure, as suggested by triple stage mass spectrometric (MS3) experiments. Dimeric adducts comprised of meta- and/or para-substituted pyridines (unhindered pyridines) display an excellent linear correlation between the fragment ion abundance ratio ln [Py1[OCNCO]+/Py2[OCNCO]+] and the proton affinity difference of the pyridines. On the assumption that the effective temperature of the [OCNCO]+ -bound dimers is similar to that of the corresponding Cl+-bound dimers, [OCNCO]+ affinities of the substituted pyridines relative to pyridine are estimated to be 3-MePy 2.3, 4-MePy 3.2, 3-EtPy 3.5, 4-EtPy 4.1, 3,5-diMePy 4.9 and 3,4-diMePy 5.6 kcal mol−1 (1 kcal = 4.184 kJ). A linear relationship between the relative [OCNCO]+ cation affinity and the relative proton affinity (PA) is derived as relative [OCNCO]+ affinity (kcal mol−1) = 0.96 ΔPA, using the assumed effective temperature of 555 K. Dimers consisting of ortho-substituted pyridines display substantial steric effects between the ortho-substituted alkyl group and the central [OCNCO]+ cation. A set of gas-phase steric parameters (Sk) is determined and steric effects are ordered 2-MePy (-1.39) <2,5-diMePy (-3.02) < 2,4-diMePy (-3.15) < 2,3-diMePy ( −3.29) < 2,6-diMePy (-5.09) < 2,4,6-triMe (-6.13). A greater steric effect is experienced in the [OCNCO]+ system than in the corresponding Cl+ system, owing to the larger central ion in Py[OCNCO]+ Py. Structural and electronic information regarding the bond angles, bond lengths and charge density distributions in [OCNCO]+, Py[OCNCO]+ and Py[OCNCO]Py+ was obtained from ab initio calculations. The calculations show that [OCNCO]+ is linear with high positive charge densities on the carbon atoms. The calculations also reveal that the Py[OCNCO]+ monomer is a planar ion with the nitrogen atom of pyridine bound to a carbon atom of the [OCNCO]+ cation, and that the Py[OCNCO]Py+ dimer is a symmetrical ion in which the nitrogen atoms on the pyridine molecules bind to the carbon atoms of the central cluster ion, [OCNCO]+.