By differential scanning calorimetry (DSC) the reaction enthalpies of the thermal splitting of the following photochemically produced dimers of meso-substituted anthracenes in fluid solutions were determined: the head-to-tail (ht) dimers of 9-decylanthracene (DEA) and 9-decyloxyanthracene (DOA) in hydrocarbon solvents, and the head-to-head (hh) dimer of 9-methoxyanthracene (MOA) and the mixed hh dimer of 9-methoxyanthracene and 9-methoxy-10-methylanthracene (MMOA) in chlorinated solvents. The molar reaction enthalpy (in kJ mol-1) is found to be lower for the ht dimers (-28 kJ mol-1, DEA and -29 kJ mol-1, DOA) than for the hh dimers (-43 kJ mol-1, MOA and -44 kJ mol-1, MMOA) with an estimated precision of ±3 kJ mol-1 each. Quantum mechanical computations give energy differences for the thermal splitting of dianthracene and the two dimers of 9-methoxyanthracene in reasonable agreement with the reaction enthalpies observed. An analysis of the change in bond energies caused by the dimerization reveals that the relative stability of the dimer is mainly caused by a large increase in bond strength of the lateral benzene rings on dimerization.
通过差示扫描量热法(
DSC)测定了下列光
化学生成的中取代
蒽二聚体在流体溶液中的热裂解反应焓:烃类溶剂中
9-癸基蒽(
DEA)和 9-癸氧基
蒽(
DOA)的头尾(ht)二聚体,以及
氯化溶剂中
9-甲氧基蒽(MOA)的头顶(hh)二聚体和
9-甲氧基蒽和 9-甲氧基-10-甲基
蒽(MMOA)的混合 hh 二聚体。发现 ht 二聚体的摩尔反应焓(kJ mol-1)(-28 kJ mol-1,
DEA 和 -29 kJ mol-1,
DOA)低于 hh 二聚体(-43 kJ mol-1,MOA 和 -44 kJ mol-1,MMOA),估计精度分别为 ±3 kJ mol-1。量子力学计算得出的二
蒽和
9-甲氧基蒽的两种二聚体热裂解的能量差异与观察到的反应焓基本一致。对二聚化引起的键能变化的分析表明,二聚物的相对稳定性主要是由二聚化时侧向苯环键强度的大幅增加引起的。