Organic Materials Research Group, Department of Chemistry, Vanderbilt University, Nashville, Tennessee 37235, USA.
Inorg Chem. 2012 May 7;51(9):5353-9. doi: 10.1021/ic300298e. Epub 2012 Apr 24.
The apparent ionization constants pK(a)' for series of carboxylic acids closo-1-CB(9)H(8)-1-COOH-10-X (1) and closo-1-CB(11)H(10)-1-COOH-12-X (2), where X = H, I, n-C(6)H(13), (+)NMe(3), (+)N(2), (+)SMe(2), OC(5)H(11), were measured in EtOH/H(2)O (1/1, v/v) at 24 °C. Correlation analysis of the pK(a)' values using Hammett substituent constants σ(p)(X) gave the reaction constant ρ = 0.87 ± 0.04 for series 1 and ρ = 1.00 ± 0.09 for series 2. These values are higher than for derivatives of PhCH═CHCOOH (ρ = 0.70 ± 0.09 in 55% EtOH) and correspond to 56% and 65% efficiencies in transmission of electronic effects by closo-1-CB(9)H(10) (E) and closo-1-CB(11)H(12) (F), respectively, as compared to benzene (A). Experimental results were supported with DFT calculations of relative acidity for series of acids derived from A, E, and F in aqueous medium.
系列羧酸 closo-1-CB(9)H(8)-1-COOH-10-X (1) 和 closo-1-CB(11)H(10)-1-COOH-12-X (2) 的表观离解常数 pK(a)'，其中 X = H、I、n-C(6)H(13)、(+)NMe(3)、(+)N(2)、(+)SMe(2)、OC(5)H(11)，在 24°C 的 EtOH/H(2)O (1/1，v/v) 中进行了测量。使用哈米特取代常数 σ(p)(X)对 pK(a)' 值进行相关分析，得到了 ρ = 0.87 ± 0.04 的反应常数，用于系列 1，以及 ρ = 1.00 ± 0.09 的反应常数，用于系列 2。这些值高于 PhCH═CHCOOH 的衍生物（在 55% EtOH 中 ρ = 0.70 ± 0.09），并且分别对应于 closo-1-CB(9)H(10) (E) 和 closo-1-CB(11)H(12) (F) 传递电子效应的效率为 56%和 65%，与苯 (A) 相比。实验结果得到了 DFT 计算的支持，该计算研究了源自 A、E 和 F 的酸系列在水介质中的相对酸度。
