Six Low-Lying Isomers of C₁₁H₈ Are Unidentified in the Laboratory–A Theoretical Study

Isomers of C11H8 have been theoretically examined using density functional theory and coupled-cluster methods. The current investigation reveals that 2aH-cyclopenta[cd]indene (2), 7-ethynyl-1H-indene (6), 4-ethynyl-1H-indene (7), 6-ethynyl-1H-indene (8), 5-ethynyl-1H-indene (9), 7bH-cyclopenta[cd]indene (10) remain elusive till date in the laboratory. puckered low-lying isomer 2 lies at 9 kJ mol–1 below experimentally known molecule, cyclobuta[de]naphthalene (3), fc-CCSD(T)/cc-pVTZ//fc-CCSD(T)/cc-pVDZ level theory. 36 above thermodynamically most stable isomer, 1H-cyclopenta[cd]indene (1), same level. It is identified 1,2-H transfer from 1 yields 2H-cyclopenta[cd]indene (14) subsequent shift 14 2. Appropriate transition states identified, intrinsic reaction coordinate calculations carried out B3LYP/6-311+G(d,p) Recently, 1-ethynyl-1H-indene (11) has detected synchrotron-based vacuum ultraviolet ionization mass spectrometry. 2-Ethynyl-1H-indene (4) 3-ethynyl-1H-indene (5) synthetically characterized past. While derivatives isolated elsewhere, parent compound remains unidentified Although a key elemental composition astronomical interest for formation polycyclic aromatic hydrocarbons interstellar medium, none its isomers by rotational spectroscopy though they are having permanent dipole moment (μ ≠ 0). Therefore, energetic spectroscopic properties computed, present necessitates new synthetic studies on C11H8, particular 2, 6–10, also all isomers.