Table 3.

Thermodynamic data for the thermal reactions from quadricyclanes 16 a–d and 17 to norbornadienes 4 a–d and 5, determined in toluene.

Entry	ΔH ≠ [kJ mol−1]	ΔS ≠ [J K−1 mol−1]	t 1/2 [a] [h]
16 a $\to$ 4 a	104	5.57	22.0
16 b $\to$ 4 b	102	3.86	15.8
16 c $\to$ 4 c	101	5.65	7.43
16 d $\to$ 4 d	92.5	−19.1	5.05
17 $\to$ 5	112	−1.31	1320

[a] Half‐lives of the photoisomers 16 a–d and 17 determined from Eyring parameters at 25 °C.