Nucleophilic Displacement Reaction of Benzyl Systems

在一定的DMA浓度范围内，研究了取代苄基芳烃磺酸盐与一系列取代N，N-二甲基苯胺在乙腈中的亲核取代反应。发现苯甲酰基与p-OMe-m-Cl相比具有更多的电子释放取代基，相对于DNA具有同步的一阶和二阶速率。在MeCN中，利用^<18>O/^<16>O同位素取代引起的烷氧碳分裂^<13>C- nmr信号，测定了对甲氧基苄基-1-^<13>C - tosyate -s ^<18>O_2与N，N-二甲基苯胺的Menschutkin反应中，起始磺酸盐内的^<18>O-置乱反应是典型的S_N2置换反应。结果表明，在非溶化溶剂MeCN中，典型的S_N2反应中存在碳阳离子中间体，从而得出S_N1和S_N2过程截然不同的结论，这些结果不能证明在该反应中S_N1和S_N2之间存在单一机制的中间体。通过测定质子转移平衡，确定了顺式2-芳基-2-丁烯的气相碱度。取代基对烯烃共轭酸离子α -乙基- α -甲基苄基阳离子稳定性的影响与α -cumyl阳离子的影响完全一致，表明α， α -二烷基苄基阳离子可以用LArSR分析给出的r值为1.0来表征。这使得我们可以根据扭曲的α， α -二烷基苄基阳离子的r值和平面α， α -二烷基苄基阳离子的r_<max>=1.0，通过方程r/r_<max>=cosrheta来估计苯基位点与苯体系之间的扭转角（rheta），得到α -t-丁基- α -甲基苄基阳离子的rheta=29^o。测定了激光闪光光解技术生成的-取代-对甲氧基苯基乙烯基阳离子在含有少量乙醇的乙腈中衰变速率常数。取代基对反应速率常数的影响可以用乙烯基阳离子稳定性和阳离子中心周围位阻的变化来解释。相反，对-环丁基和-环庚基衍生物所观察到的高速率常数不能简单地解释。少

Nucleophilic substitution reaction of substituted benzyl arenesulfonates with a series of substituted N,N-dimethyl anilines in acetonitrile have been studied over a range of DMA concentrations. It is found that benzyl tosylates having more electron-releasing substituents than p-OMe-m-Cl have concurrent first-and second-order rates with respect to DNA.The ^<18>O-scrambling within starting sulfonate during the Menschutkin reaction of p-methoxybenzyl-1-^<13>C tosylate-S^<18>O_2 with N,N-dimethylanilines which is typical S_N2 displacement reaction, was determined in MeCN utilizing the split ^<13>C-NMR signals of alkoxy carbon induced by ^<18>O/^<16>O isotopic substitution. It has been shown that the carbocationic intermediates exist in the typical S_N2 reaction in non-solvolyzing solvent MeCN,leading to the conclusion that the S_N1 and S_N2 processes are quite distinct that these results afford no evidence for a singly mechanism intermediate between S_N1 and S_N2 in this reaction.The gas p … More hase basicities of cis 2-aryl-2-butenes have been determined by measuring proton transfer equilibria. It has been shown that the substituent effect on the stability of the conjugate acid ion of the olefin, alpha-ethyl-alpha-methylbenzyl cation, is in complete agreement with that of alpha-cumyl cation, suggesting that alpha, alpha-dialkyl benzyl cations can be characterized by the r value of 1.0 given by the LArSR analysis. This allows us to estimate the torsional angle (rheta) between the benzylic site and the benzene system from the r value of the twisted alpha, alpha-dialkylbenzyl cation and r_<max>=1.0 for the planar alpha, alpha-dialkylbenzyl cation by the equation r/r_<max>=cosrheta, giving rheta=29^o for alpha-t-butyl-alpha-methylbenzyl cation.The decay rate constants of beta-substituted alpha-p-methoxyphenylvinyl cations which are generated by the laser flash photolysis techniques have been determined in acetonitrile involving a small amount of ethanol. The change of rate constants with beta-substituents could be interpreted by the change in stability of vinyl cations and in steric hindrance around cationic center. On the contrary, exalted rate constants observed for beta-cyclobutylidene and beta-cycloheptylidene derivatives cannot be explained simply. Less