Heats of Formation of [2.2]Paracyclophane-1-ene and [2.2]Paracyclophane-1,9-diene − An Experimental Study

The enthalpies of formation [Δ

(g)] of tricyclo[8.2.2.24,7]hexadeca-1(13),2,4(16),5,7(15),10(14),11-heptaene (2, 1,2-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1-ene) and tricyclo[8.2.2.24,7]hexadeca-1(13),2,4(16),5,7(15),8,10(14),11-octaene (3, 1,2,9,10-dehydro[2.2]paracyclophane or [2.2]paracyclophane-1,9-diene) have been determined by measuring their heats of combustion in a microcalorimeter
and their heats of sublimation by the transpiration method. Values of the strain energies (SE) [SE(2) =
34.7 kcal mol-1, SE(3) = 42.0 kcal mol-1] have been derived from the gas-phase heats of formation and
are compared with those from MM3 and PM3 calculations and with the corresponding value SE(1) = 30.1
kcal mol-1 for the parent tricyclo[8.2.2.24,7]hexadeca-1(13),4(16),5,7(15),10(14),11-hexaene (1, [2.2]paracyclophane). The higher strain energies of 2 and 3 (by 4.6 and 11.9 kcal mol-1) are in accord with the
well-known increased reactivities of their aromatic rings as a consequence of their increased bending. As
revealed by an X-ray crystal structure analysis, the bending in the monoene 2 corresponds to that of 1 and
3 at one of two bridging corners.

通过微量热仪测定燃烧热、采用蒸腾法测定升华焓，确定了三环[8.2.2.24,7]十六碳-1(13),2,4(16),5,7(15),10(14),11-七烯（化合物2，即1,2-脱氢[2.2]对环芳烷或[2.2]对环芳烷-1-烯）与三环[8.2.2.24,7]十六碳-1(13),2,4(16),5,7(15),8,10(14),11-八烯（化合物3，即1,2,9,10-脱氢[2.2]对环芳烷或[2.2]对环芳烷-1,9-二烯）的气相生成焓[Δ(g)]。从气相生成焓推导得到二者的环张力能（strain energies）数值：SE(2)=34.7 kcal·mol⁻¹，SE(3)=42.0 kcal·mol⁻¹，并将其与MM3、PM3计算得到的环张力能，以及母体化合物三环[8.2.2.24,7]十六碳-1(13),4(16),5,7(15),10(14),11-六烯（化合物1，[2.2]对环芳烷）的环张力能SE(1)=30.1 kcal·mol⁻¹进行对比。化合物2和3更高的环张力能（分别高出4.6和11.9 kcal·mol⁻¹），与其芳香环因弯曲程度增加而表现出更强反应活性这一公认结论相符。X射线晶体结构分析显示，单烯烃化合物2的弯曲程度与化合物1和3的其中一个桥接转角处的弯曲程度一致。