54826-91-4Relevant academic research and scientific papers
Structural effects on interconversion of oxygen-substituted bisketenes and cyclobutenediones
Fu, Nanyan,Allen, Annette D.,Kobayashi, Shinjiro,Tidwell, Thomas T.,Vukovic, Sinisa,Matsuoka, Takeshi,Mishima, Masaaki
, p. 1768 - 1773 (2008/09/18)
(Graph Presented) Cyclobutenediones 5 disubstituted with HO (a), MeO (b), EtO (c), i-PrO (d), t-BuO (e), PhO (f), 4-MeOC6H4O (g), 4-O2NC6H4O (h), and 3,4-bridging OCH 2CH2O (i) substituents upon laser flash photolysis gave the corresponding bisketenes 6a-i, as detected by their distinctive doublet IR absorptions between 2075 and 2106 and 2116 and 2140 cm-1. The reactivities in ring closure back to the cyclobutenediones were greatest for the group 6b-e, with the highest rate constant of 2.95 ×107 s -1 at 25°C for 6e (RO = t-BuO) in isooctane, were less for 6a (RO = OH, k = 2.57 × 106 s-1 in CH3CN), while 6f- i were the least reactive, with the lowest rate constant of 3.8 × 104 s-1 in CH3CN for 6h (RO = 4-O 2NC6H4O). The significantly reduced rate constants for 6f-i are attributed to diminution of the electron-donating ability of oxygen to the cyclobutenediones 5f-h by the ArO substituents compared to alkoxy groups and to angle strain in the bridged product cyclobutenedione 5i. The reactivities of the ArO-substituted bisketenes 6f-h in CH3CN varied by a factor of 50 and gave an excellent correlation of the observed rate constants log k with the σp constants of the aryl substituents. Computational studies at the B3LYP/6-31G(d) level of ring-closure barriers are consistent with the measured reactivities. Photolysis of squaric acid (5a) in solution provides a convenient preparation of deltic acid (7).
Molecular structure and infrared spectra of 3,4-dihydroxy-3-cyclobutene-1,2-dione; experimental matrix isolation and theoretical Hartree-Fock and post Hartree-Fock study
Rostkowska, Hanna,Nowak, Maciej J.,Lapinski, Leszek,Smith, Dayle,Adamowicz, Ludwik
, p. 959 - 968 (2007/10/03)
The infrared spectra of 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid) isolated in low-temperature Ar and N2 matrices are reported. The comparison of the experimental spectra with those theoretically calculated at HF/6-31 + + G**, MP2/6-31G** and DFT(B3-LYP)/6-31 + +G** levels shows that the molecules of the compound isolated in low-temperature matrix adopt the structure with C2v symmetry. This structure is different from the one which was found in the crystal. Theoretical calculations of relative energies of C2v and Cs structures predict the C2v conformation to be lower in energy by 8 kJ mol-1. Good agreement between the experimental and theoretical spectra allowed for a reliable assignment of the observed IR absorption bands.
Ethynediol: Photochemical generation and matrix-spectroscopic identification
Maier, Guenther,Rohr, Christine
, p. 307 - 309 (2007/10/03)
Irradiation of squaric acid (4) in an argon matrix at 10 K leads to ethynediol (dihydroxyacetylene) (1) via bis(hydroxyketenyl) 5 and deltic acid (6). The identification of 1 is based on the comparison between the experimental and calculated IR spectrum. VCH Verlagsgesellschaft mbH, 1996.
