The energetics of the isomeric anthrols

Abstract

We report the results of geometry optimized MP2(FULL)/6-31G(d) quantum chemical calculations with zero-point vibrational energies and thermal corrections of the isomeric 1-, 2-and 9-anthrols and the tautomeric anthrone. We find that 1-and 2-anthrols have nearly the same enthalpy of formation and are some 6 kJ mol À1 more stable than their 9-isomer in accord with intuition based on steric hindrance. We find that anthrone is more stable than 9-anthrol by 13.7 AE 6.4 kJ mol À1 , in satisfactory agreement with the value of 23 AE 8 kJ mol À1 suggested elsewhere by experiment and its associated analysis.

Ultraviolet photolysis of anthracene in H2O interstellar ice analogs: Potential connection to meteoritic organics

“…The low yield of the 9-anthrone and the high yield of 9,10-anthraquinone cannot be explained by thermodynamic stability alone, since the 9-anthrone is more thermodynamically favorable than the 1-and 2-anthrols (Notario et al 2004). However, it is possible that the 9-anthrone, once formed, continues reacting under additional UV exposure to form the 9,10-anthraquinone, the most abundant product observed.…”

“…Anthracene, which possesses three rings, has even more regiochemical possibilities, with three distinctly different sites for mono-oxidation and 15 possible isomeric combinations for double addition of oxygen. Of the three possible singly oxidized positions, two (the 1-and 2-sites) are most stable in the alcohol form and one (the 9-site) is most stable as the ketone (Notario et al 2004). The 9,10-anthraquinone is more stable than the singly oxidized compounds based on enthalpy of formation (Ribeiro da Silva et al 1989).…”

“…The similar production of the two anthrols may be a reflection of their nearly equal thermodynamic stability (Notario et al 2004). Previous laboratory and theoretical studies of naphthalene suggest a radical cation intermediate in the cryogenic water ice leading to the UV-driven formation of naphthols upon eventual warmup (Bernstein et al 1999;Ricca and Bauschlicher 2000;Gudipati and Allamandola 2003).…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 21, 2010) and the discipline

“…It is entirely plausible that the 1-carboxylic acid is less stable than its 2-isomer much as naphthalene-1-carboxylic acid is some 8 kJ mol -1 less stable than its 2-isomer [267]. Now, what are the relative stabilities of the 1-, 2-, and 9-carboxylic acids of anthracene [268]: only the enthalpy of the last and presumably most sterically hindered species is the value known from experiment [269].…”

Interplay of Thermochemistry and Structural Chemistry, the Journal (Volume 13, 2002) and the Discipline

“…This seems unlikely. Yet, given the lack of measurements of the enthalpies of formation of substituted aromatic species beyond those of benzene and naphthalene [98], can we really preclude the above bianthryl/biphenanthryl enthalpy differences?…”