Quinones. Part 9. Stability of quinones toward water. Synthesis of a 1,7-naphthoquinone

Abstract

Calculated relative reactivities of the benzo-, naphtho-, and anthraquinones toward water (using perturbation MO theory) reflect well the sequence of stability of the known quiñones. This method may be used to predict the stability of unknown quiñones toward water or other nucleophiles. A 1,7-naphthoquinone, 3,6-di-tert-butyl-8-methyl-l,7-naphthoquinone (24), is described for the first time. It is prepared in a 13-step synthesis. On the basis of PMO calculations and analogous cases the alkyl groups in 24 were considered to be adequate to shield the 1,7-naphthoquinoid system from attack of water and dimerization. 24 shows an unexpected low stability. According to MNDO calculations the alkyl groups cause a high steric strain in the molecule, possibly responsible for the observed low stability.

Photophysical Characterization of a Benzo-Fused Analogue of Brooker’s Merocyanine: Solvent Polarity and pH Effects

“…This behavior can be explained in part by the relative instability of 2,6-naphthoquinones, which are regarded as nonaromatic. 20,21 While HNEP + is weakly to moderately emissive in the solvents investigated (Table 1), no emission for NEP could be detected. The difference in ground state and excited state dipoles can be calculated from a Lippert plot: 22 the slope obtained from a plot of the Stokes shift (Δν) versus the solvent orientation polarizability yields the term 2(Δμ) 2 /hcr 3 (Figure 6).…”

“…While BM exhibits some vibronic structure (Figure , in blue), the absorption of NEP is broad and featureless, which is typical of a charge transfer process. This behavior can be explained in part by the relative instability of 2,6-naphthoquinones, which are regarded as nonaromatic. , …”

“…The slope of the line corresponds to the term 2(Δμ) 2 /hcr 3 . 21,22 For HNEP + , Δμ = 17.9 D (R 2 = 0.87) and 16.7 D (R 2 = 0.83) in protic and aprotic solvents, respectively. LUMO is polarized toward the electron-withdrawing pyridinium moiety.…”

Charge Transfer Pathways in Three Isomers of Naphthalene-Bridged Organic Mixed Valence Compounds

“…Only resonance structures with the naphthylene bridge in a biradical state are conceivable in this case, and such structures are energetically very unfavorable. This manifests in the fact that 1,8-naphthoquinone is not a known stable molecule, contrary to 1,5- and 2,6-naphthoquinone . Moreover, the naphthyl biradical resonance structures in Scheme c leads to cross-conjugation of attached redox centers, and consequently their mutual (through-bond) electronic communication is expected to be very weak in this limit.…”

Attempts to find a solution to the problem of atropisomer interconversion in 1,8-diarylnaphthalenes and 5,6-diarylacenaphthenes

“…Concentration in vacuo followed by recrystallisation (40 : 60 petroleum ether) yielded (4.05 g, 96%) 4-bromo-2-tert-butyl-6-methylanisole as a colourless liquid, which was identical to that reported in the literature. 20…”