Double Aromaticity and Anti-aromaticity in Small Carbon Rings.

Sonsoles Martín-Santamaría and Henry S. Rzepa*

Department of Chemistry, Imperial College of Science, Technology and Medicine, London, SW7 2AY, UK.

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Table. Calculated Energies [kcal mol^-1 for AM1, Hartree for RHF/6-31G(d)] and NICS(0) values (ppm)

Species	AM1	B3LYP/6-31G(d)	NICS	Orbital occupancy
C₁₀	403.8	-380.6661	-28.9	p(E), s(E), s(E), p(E), p, s
B₅N₅	-57.9	-398.2935	-2.5	p(E), s(E), p(E), s(E), p, s
C₈N₂	358.7	-413.9714	-16.7	s, s, p, p, s, s, p, p, s, p, s
C₁₂²⁺	954.2	- 456.0285	+32.4	p, s(E), p(E), s(E), p(E), p, s
C₁₀B₂	504.7	-430.3801	-11.0	s, p, s, s, p, p, s, s, p, p, s
C₁₂^a	--	-456.7770	-8.7	--
C₁₂^b	--	-456.7452	-31.5	--
C₁₂	438.5	-456.7878	+50.0	p, s, s(E), p(E), s(E), p(E), p, s
C₁₄	465.1	-533.0193	-35.6	s(E), p(E), s(E), p(E), s(E), p(E), p, s
C₁₁H₂	350.9	-419.9766	-13.4	--
C₁₃H₂	387.3	-496.1407	+6.8	--
C₁₉	664.5	-723.2905	-11.0	--

^a Triplet state. ^b Quintet state.

Figure 2. AM1 Calculated orbitals for (a) C11H2 (HOMO-6) and (b) C19 (HOMO-15).