The balance between endo- and exo-cyclic CN fission in the hydrolysis of N-aroyl β-lactams shows that the difference in reactivity between strained β-lactams and their acyclic analogues is minimal. Attack of hydroxide ion occurs preferentially at the exocyclic acyl centre rather than that of the β-lactam during the hydrolysis of N-p-nitrobenzoyl β-lactam. In general, both endo- and exo-cyclic CN bond fission occurs in the alkaline hydrolysis of N-aroyl β-lactams, the ratio of which varies with the aryl substituent. Hence, the Brønsted β-values differ for the two processes: 0.55 for the ring-opening reaction and 1.54 for the exocyclic CN bond fission reaction. For the pH-independent and acid-catalysed hydrolysis of N-benzoyl β-lactam, less than 3% of products are derived from exocyclic CN bond fission. Key words: β-lactams, hydrolysis, linear free energy relationships, strain.
在N-酰基β-内酰胺水解中,内环和外环C-N裂解之间的平衡表明,受应变β-内酰胺和它们的非环结构类似物之间的反应性差异是最小的。在N-p-硝基苯甲酰基β-内酰胺水解过程中,羟根离子的攻击优先发生在外环酰基中心而不是β-内酰胺中心。一般来说,在N-酰基β-内酰胺的碱性水解中,内环和外环C-N键裂解都会发生,其比例随芳基取代基而变化。因此,这两个过程的Brønsted β值不同:环开启反应为-0.55,外环C-N键裂解反应为-1.54。对于N-苯甲酰基β-内酰胺的pH无关和酸催化水解,少于3%的产物来自外环C-N键裂解。关键词:β-内酰胺,水解,线性自由能关系,应变。