An Experimental and Computational Study about the Effect of a Spirocyclopropane Group on the Solvolysis Rates of Bridgehead Triflates
作者:Antonio García Martínez、Enrique Teso Vilar、Santiago de la Moya Cerero、José Osío Barcina、Pedro C. Gómez
DOI:10.1021/jo990701i
日期:1999.7.1
cyclopropyl group adjacent to the bridgehead cation leads to an increase of the strain energy. This fact has two opposite effects on the solvolysis rate: (a) the strain energy hinders the flattening of the cation and, hence, originates a rate depression, and (b) the strained C-C bonds are prone to stabilize the cation at C(1) by sigma-delocalization, which provokes a rise of the solvolysis rate. Both
获得7',7'-二甲基螺[环丙烷-1,2'-降冰片烷] -1'-三氟甲磺酸酯(9),并在不同温度下测定其在60%缓冲乙醇水溶液中的溶剂分解速率。通过力场法,半经验法和从头算[B3LYP / 6-31g(d)]方法研究了9种桥头衍生物和其他桥头衍生物(13-17,参见表1)的溶剂分解行为。阳离子9(+)是几乎垂直构型的略呈金字塔形的环丙基羰基阳离子,显示出sp(2)-like杂交。它对电子的高需求激发了C(5)-C(6)和C(4)-C(7)键的σ参与度的提高。与桥头阳离子相邻的环丙基的引入导致应变能的增加。这个事实对溶剂分解速率有两个相反的影响:(a)应变能阻碍了阳离子的扁平化,并且 因此,导致速率降低,(b)应变的CC键易于通过sigma-localization稳定C(1)处的阳离子,从而引起溶剂分解速率的提高。两种影响仅通过B3LYP / 6-31g方法得到解释。我们的计算结果并未证实