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在25℃时及0.10M NaClO_4存在下,N-苯氨基乙酸((?)G)和 N-α-萘氨基乙酸(αNG)在30%(体积)乙醇中的表观离解常数用 pH 法测定为(?)G:pK_(COOH)=2.69,pK_(R_2NH_2)~+=4.72;αNG:pK_(COOH)=2.64,pK_(R_2NH_2)~+=10.83。为便于比较,氨基乙酸(G)的离解常数亦在相同情况下测定为 pK_(COOH)=2.71,pK_(R_2NH_2)~+=9.30。(?)G 和αNG 的硷性强度相差如此巨大,主要是由于后者有位阻效应之故。(?)G 的硷性比 G 的弱得多,因共轭效应起决定性的作用。改变溶剂的介电常数的结果是使氨基酸的酸硷性均减弱。
The apparent dissociation constants of N-phenylaminoacetic acid ((?) G) and N-α-naphthylaminoacetic acid (αNG) in 30% by volume of ethanol in the presence of 0.10 M NaClO 4 at 25 ° C were determined by the pH method (?) G: pK_ (COOH) = 2.69, pK_ (R_2NH_2) ~ + = 4.72; αNG: pK_ (COOH) = 2.64, pK_ (R_2NH_2) ~ + = 10.83. For the sake of comparison, the dissociation constant of glycine (G) was also determined as pK COOH = 2.71 and pK R 2 NH 2 + = 9.30 under the same conditions. (?) The great difference between the alkaline strength of G and αNG is due to the steric hindrance of the latter. (?) G is much weaker than G and plays a decisive role due to the conjugation effect. As a result of changing the dielectric constant of the solvent, the acidity of the amino acid is weakened.