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采用B3LYP/6-31G~(**)方法在Gaussian03程序下,优化去质子化卟吩(PH~-)和单质子化卟吩(PH_3~+)的结构后发现,PH~-和卟吩(PH_2)一样具有平面构型,但PH_3~+的3个内氢原子存在明显的静电排斥和空间位阻,构型发生非平面扭曲。在相同的条件下优化得到PH~-和PH_3~+内氢迁移反应的过渡态,通过与卟吩(PH_2)比较,分析质子化对内氢迁移反应速率的影响。结果表明,PH~-的过渡态构型与PH_2过渡态的结构参数基本相同,内氢迁移速率相差不大(PH~-仅为PH_2的一半);但PH_3~+的过渡态构型偏离平面的程度远小于平衡态,从平衡态到过渡态,共轭效应明显增强,PH_3~+的活化焓远小于PH_2,故PH_3~+的内氢迁移速率明显大于PH_2。
The structure of deprotonated porphine (PH ~ -) and mono protonated porphine (PH_3 ~ +) was optimized by B3LYP / 6-31G ~ (**) method under Gaussian03 program. (PH_2). However, there are obvious electrostatic repulsions and steric hindrances in the three hydrogen atoms of PH_3 ~ +, and the non-planar distortion of the configuration occurs. Under the same conditions, the transition states of intramolecular hydrogen transfer between PH ~ - and PH_3 ~ + were optimized, and the effect of protonation on the rate of intramolecular hydrogen transfer was analyzed by comparison with PH_2. The results show that the transition state configuration of PH ~ - is almost the same as that of PH_2 transition state, and the migration rates of internal hydrogen are not different (PH ~ - only half of PH_2). However, the transition state configuration of PH_3 ~ + deviates from the plane Is much smaller than the equilibrium state. From the equilibrium state to the transition state, the conjugation effect is obviously enhanced. The activation enthalpy of PH 3 ~ + is far less than that of PH 2, so the migration rate of PH 3+ is obviously higher than that of PH 2.