Table 1.

Gibbs free energies^[a] relative to I along the reaction sequence shown in Scheme 8. Also given are the lengths of the forming (N5–C4a) and breaking (C4a–X) bonds in the transition state

	ΔG [kJ mol−1]			d≠ [Å]
	TS	III	III++X−	IV	N5–C4a	C4a–X
a	103	−65	−81	−79	1.85	1.40
b	98	−57	−74	−84	1.88	1.39
c	93	−60	−72	−93	1.87	1.39
d	72	−52	−71	−89	1.96	1.37
e	115	−70	−90	−78	1.84	1.41
f	90	−51	−59	−88	1.88	1.39
g	112	−61	−77	−76	1.87	1.40
h	120	−126	−133	[b]	1.88	1.87
avac[c]	112	80[d]	440	−80	1.81	1.39

[a] Calculated at M06-2X/def2-TZVP+ level in polarisable continuum MeCN (ε_r=22.5) for T=383 K, P=320 kPa. [b] The 6-chlorophenanthridine IVh is not a stable minimum, but dissociates into the ion pair IIIh during structure optimisation. [c] Calculated in vacuum. [d] Energy of IIa_vac. In vacuum, the ion pair IIIa_vac is not stable, but collapses to IIa_vac.