4-methoxybenzyl carbocation | 29180-19-6

• 分子结构分类: 有机化合物 - 苯类化合物 - 苯酚醚
• 英文名称: 4-methoxybenzyl carbocation
• 英文别名: p-methoxybenzyl cation；4-Methoxybenzylkation；4-methoxy-benzylium；p-Methoxybenzylkation；1-methoxy-4-methylbenzene
• CAS: 29180-19-6；1228701-75-4
• 化学式: C₈H₉O
• 分子量: 121.159
• InChiKey: UMZDIRRLEWMTEI-UHFFFAOYSA-N

计算性质

• 辛醇/水分配系数(LogP)：
  2.7
• 重原子数：
  9
• 可旋转键数：
  1
• 环数：
  1.0
• sp3杂化的碳原子比例：
  0.12
• 拓扑面积：
  9.2
• 氢给体数：
  0
• 氢受体数：
  1

反应信息

• 作为反应物：
  描述：

  4-methoxybenzyl carbocation 在 potassium chloride 、 盐酸 作用下， 生成 4-甲氧基氯苄
  参考文献：
  名称：

  4-甲氧基苄基氟溶剂解的氢键和催化

  摘要：

  k(o) = 8.0 x 10(-3) s(-1) 和 k(H) = 2.5 x 10(-2) M(-1) s(-1) 的值分别被确定为自发性以及 4-甲氧基苄基氟 (1-F) 的酸催化裂解形成 4-甲氧基苄基碳正离子 (1+)。确定 k(F) = 1.8 x 10(7) M(-1) s(-1) 和 k(HF) = 7.2 x 10(4) M(-1) s(-1) 的值用于添加F- 和 HF 为 1+ 以进行微观反方向反应。有证据表明，HF 与 1+ 的可逆加成得到 1-F + H+ 是通过协同反应机制进行的。氟离子和中性 HF 对 1+ 的反应性之间相对较小的 250 倍差异归因于 F- 的强水溶剂化趋势降低其亲核反应性，并且与通常的逐步途径相比具有协同优势用于添加 HF。在 pH 1.7 的 0.80 M 氰乙酸盐缓冲液中，从一般酸催化中裂解 1-F 的过渡态没有明显的稳定性。估计 1-F

  DOI：

  10.1021/ja026849s
• 作为产物：
  描述：

  4-methoxybenzyl pentafluorobenzoate 以 水 为溶剂， 生成 4-methoxybenzyl carbocation
  参考文献：
  名称：

  4-甲氧基苄基衍生物的同步逐步和协同取代反应和4-甲氧基苄基碳正离子的寿命

  摘要：

  4-甲氧基苄基氯 (1)、五氟苯甲酸酯和 3,5-二硝基苯甲酸酯在 50:50 (v/v) 三氟乙醇/水中的反应速率在叠氮离子浓度方面为零级。这些反应通过捕获 4-甲氧基苄基碳正离子中间体获得了良好的叠氮化物加合物收率，并且对 4-MeOArCH 2 Cl 的反应也有很强的常见氯离子抑制作用。叠氮化物和溶剂加合物的产率给出速率常数比 k az /ks =25 M -1 ，氯离子效应分析给出 k Cl /ks =9 M -1 ，用于碳阳离子中间体的分配。叠氮离子与碳正离子中间体的反应作为溶剂和氯离子反应的扩散控制“时钟”。在机理和 80 离子化程度较低的溶剂中存在溶剂引起的变化：20 (v/v) 和 70:30 (v/v) 丙酮/水；叠氮离子与 1 的反应通过碳正离子中间体的捕获和协同的双分子取代反应产生叠氮化物加合物

  DOI：

  10.1021/ja00182a009

文献信息

• Lifetimes and UV-visible absorption spectra of benzyl, phenethyl, and cumyl carbocations and corresponding vinyl cations. A laser flash photolysis study
  作者：Frances L Cozens、V M Kanagasabapathy、Robert A McClelland、Steen Steenken

  DOI：10.1139/v99-210

  日期：1999.12.5

  Benzyl (4-MeO, 4-Me, and 4-methoxy-1-naphthylmethyl), phenethyl (4-Me₂N, 4-MeO, 3,4-(MeO)₂, 4-Me, 3-Me, 4-F, 3-MeO, 2,6-Me₂, parent, and 4-methoxy-1-naphthylethyl) and cumyl (4-Me₂N, 4-MeO, 4-Me, parent) cations have been studied by laser flash photolysis (LFP) in 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP). In most cases styrene or α-methylstyrene precursors were employed for the phenethyl and cumyl ions, the intermediate being obtained by solvent protonation of the excited state. Benzyl cations were generated by photoheterolysis of trimethylammonium and chloride precursors. While a 4-MeO substituent provides sufficient stabilization to permit observation of cations in TFE, cations with less stabilizing substituents usually require the less nucleophilic HFIP. Even in this solvent, the parent benzyl cation is too short-lived (lifetime <20 ns) to be observed. When generated in HFIP, phenethyl cations can be seen to react with unphotolyzed styrene, giving rise to dimer cations that are observed to grow in as the initial phenethyl cation decays. The dimer cations, in common with the oligomer cations seen in cationic styrene polymerization, have a λ_max 15-20 nm higher than the monomer and react with both solvent and styrene several orders of magnitude more slowly. This stabilization relative to the phenethyl may reflect an interaction with the aryl group present at the gamma-carbon. Cations 4-MeOC₆H₄C⁺(R)-CH₃ (R = Me, Et, i-Pr, t-Bu, cyclopropyl, C₆H₅, 4-MeOC₆H₄) were generated in TFE via the photoprotonation route. The alkyl series shows that steric effects are important in the decay reaction. The cation with R = cyclopropyl is a factor of 1.5 less reactive than the cation where R = phenyl. Several vinyl cations have also been generated by photoprotonation of phenylacetylenes. ArC⁺=CH₂ has a reactivity very similar to that of its analog ArC⁺H-CH₃, the vinyl cation being slightly (factors of 2-5) shorter-lived. For the various series of cations, including vinyl, substituents in the aryl ring have a consistent effect on the λ_max, a shift to higher wavelength relative to hydrogen of 15 nm for 4-Me, 30 nm for 4-MeO, and 50 nm for 4-Me₂N.Key words: photogenerated carbocations, carbocation lifetime, styrene, photoprotonation.

  苯甲基（4-MeO，4-Me和4-甲氧基-1-萘基甲基）、苯乙基（4-Me2N，4-MeO，3,4-(MeO)2，4-Me，3-Me，4-F，3-MeO，2,6-Me2，母体和4-甲氧基-1-萘基乙基）和叔丁基（4-Me2N，4-MeO，4-Me，母体）阳离子在2,2,2-三氟乙醇（TFE）和1,1,1,3,3,3-六氟异丙醇（HFIP）中通过激光闪光光解（LFP）进行了研究。在大多数情况下，苯乙烯或α-甲基苯乙烯前体被用于苯乙基和叔丁基离子，中间体通过溶剂质子化激发态而获得。苯甲基阳离子是通过三甲基铵和氯化物前体的光异裂生成的。虽然4-MeO取代基提供了足够的稳定性以在TFE中观察到阳离子，但具有较少稳定取代基的阳离子通常需要较不亲核的HFIP。即使在这种溶剂中，母体苯甲基阳离子也太短寿命（寿命<20 ns）而无法观察到。在HFIP中生成的苯乙基阳离子可以看到与未经光解的苯乙烯反应，导致观察到的二聚体阳离子在初始苯乙基阳离子衰减时增长。与阳离子苯乙烯聚合中观察到的寡聚体阳离子一样，二聚体阳离子的λmax比单体高15-20 nm，并且与溶剂和苯乙烯反应速度慢几个数量级。相对于苯乙基的这种稳定性可能反映了与伽马碳上存在的芳基的相互作用。在TFE中通过光质子化途径生成了4-MeOC6H4C+(R)-CH3（R = Me，Et，i-Pr，t-Bu，环丙基，C6H5，4-MeOC6H4）阳离子。烷基系列表明立体效应在衰减反应中很重要。当R = 环丙基时，其反应性比R = 苯基的阳离子少1.5倍。还通过对苯乙炔的光质子化生成了几种乙烯阳离子。ArC+=CH2的反应性与其类似物ArC+H-CH3非常相似，乙烯阳离子寿命略短（2-5倍因子）。对于包括乙烯在内的各系列阳离子，芳香环中的取代基对λmax有一致的影响，相对于氢的15 nm的4-Me，30 nm的4-MeO和50 nm的4-Me2N的波长偏移。关键词：光产生的碳正离子，碳正离子寿命，苯乙烯，光质子化。
• Substituent Effect on the Stability of Benzyl Cation in the Gas Phase
  作者：Masaaki Mishima、Kiyoshi Arima、Satoshi Usui、Mizue Fujio、Yuho Tsuno

  DOI：10.1246/cl.1987.1047

  日期：1987.6.5

  Chloride ion affinities of substituted benzyl cations in the gas phase have been determined by means of an ICR mass spectrometer. The substituent effect has been analyzed in terms of the LArSR Eq., giving a ρ=13.6 and an r+=1.31.

  气相中取代的苄基阳离子的氯离子亲和力已通过ICR质谱仪测定。已根据 LArSR 方程分析取代基效应，得出 ρ=13.6 和 r+=1.31。
• Mechanisms of Benzyl Group Transfer in the Decay of (E)-Arylmethanediazoates and Aryldiazomethanes in Aqueous Solutions
  作者：Jari I. Finneman、James C. Fishbein

  DOI：10.1021/ja00120a004

  日期：1995.4

  Rate constants are reported for the buffer-independent decay of ten (E)-arylmethanediazontes in aqueous media at 25 degrees C, ionic strength 1 M (NaClO4), 4% 2-propanol, in the region of pH 4-12. The rate constants are proportional to hydrogen ion concentration at high pH and become pH independent in the low-pH region. Varying concentrations of oxyanion, amine, and hydrazine buffers over the range 0.05-0.2 M increased the pseudo-first-order rate constant for decay of the diazoates by less than 10%. The azide-water selectivities, k(2)/k(5), for partitioning of the benzyl groups in the decay of (E)-(3,5-bis(trifluoromethyl)phenyl)methanediazonate and the (3,5-bis(trifluoromethyl)phenyl)diazomethane are determined to be 0.20 and 0.21 M(-1), respectively, in phosphate buffered water and 0.27 and 0.26 M(-1), respectively, in 20/80 DMSO-water. It is concluded that these two reactants decompose, in these media, via a common free diazonium ion intermediate that is formed in the case of the diazoate upon unassisted N-O bond cleavage of the diazoic acid. A common rate-limiting step is indicated for all the diazoates by the correlation line for the plot of log k(1), the pH independent rate constant, against sigma that has a slope rho = -1.23. Product ratios for trapping of benzyl groups derived from other pairs of arylmethanediazoates and aryldiazomethanes with less electron withdrawing groups are different outside experimental error, indicating the importance of different nitrogen-separated ion pairs in these reactions. The (E)-(p-methoxy)phenyl)methane-(16)-diazoat decomposes in O-16/O-18 water to give alcohol that has an ''excess'' abundance of O-16 compared to solvent, Decomposition of the same compound in 50/50 trifluoroethanol-water with varying concentrations of azide indicates that azide ion appears to trap a limiting amount, similar to 80%, of the p-methoxybenzyl group. Quantitative analysis of the data indicates that 16% of the p-methoxybenzyl cation is trapped by solvent at the nitrogen-separated ion pair stage, in the absence of azide ion, There is a 9-fold enhancement of selectivity for trifluoroethanol at the ion pair stage that is ascribed to a proton switch initiated by the leaving hydroxide ion in the ion pair. The values of k(2)/k(5) similar to 0.2 M(-1) and k(T)/k(H) similar to 0.5-0.6 for the trifluoroethanol-water selectivity and k(ET)/k(T) similar to 1 for the ethanol-trifluoroethanol selectivity are independent of substituent in the decay of arylmethanediazoates (X = H and EWG) in water, water-trifluoroethanol (50/50), and water-trifluoroethanol-ethanol (50/40/10), respectively. It is concluded from this that the product-determining steps do not involve chemical bonding but rather rotational/translational reorientation of the nucleophiles in the first solvation sphere of the carbocation intermediates. It is concluded that the values of k(H)/k(T) = 0.5-0.6 indicate preferential solvation of the cation precursor by trifluoroethanol. It is shown that a preferential interaction for trifluoroethanol of <1 kcal/mol is required to generate the observed selectivities.
• McClelland,Robrt A.; Chan, Christopher; Cozens, Frances, Angewandte Chemie, 1991, vol. 103, # 10, p. 1389 - 1391
  作者：McClelland,Robrt A.、Chan, Christopher、Cozens, Frances、Modro, Agnieska、Steenken, Steen

  DOI：——

  日期：——
• Concurrent stepwise and concerted substitution reactions of 4-methoxybenzyl derivatives and the lifetime of the 4-methoxybenzyl carbocation
  作者：Tina L. Amyes、John P. Richard

  DOI：10.1021/ja00182a009

  日期：1990.12

  common ion effect gives k Cl /k s =9 M −1 , for partitioning of the carbocation intermediate. The reaction of azide ion with the carbocation intermediate serves as a diffusion-controlled «clock» for the reactions of solvent and chloride ion. There is a solvent-induced change in mechanism and in the less ionizing solvents of 80:20 (v/v) and 70:30 (v/v) acetone/water; the reaction of azide ion with 1

  4-甲氧基苄基氯 (1)、五氟苯甲酸酯和 3,5-二硝基苯甲酸酯在 50:50 (v/v) 三氟乙醇/水中的反应速率在叠氮离子浓度方面为零级。这些反应通过捕获 4-甲氧基苄基碳正离子中间体获得了良好的叠氮化物加合物收率，并且对 4-MeOArCH 2 Cl 的反应也有很强的常见氯离子抑制作用。叠氮化物和溶剂加合物的产率给出速率常数比 k az /ks =25 M -1 ，氯离子效应分析给出 k Cl /ks =9 M -1 ，用于碳阳离子中间体的分配。叠氮离子与碳正离子中间体的反应作为溶剂和氯离子反应的扩散控制“时钟”。在机理和 80 离子化程度较低的溶剂中存在溶剂引起的变化：20 (v/v) 和 70:30 (v/v) 丙酮/水；叠氮离子与 1 的反应通过碳正离子中间体的捕获和协同的双分子取代反应产生叠氮化物加合物