The synthesis of five-and six-membered rings 3% 4, Sb, 5% and 17% containing the structural moiety 3-pentene-l,2,5-trione, is described The chromophoric properties of these vinylogous tricarbonyls together with related compoutlds rue investigated. The conformation in solution, particularly the torsion angle rindsidechain, can be derived from measurements of coupling constants, NOE difference spectra, and force-field calculations. X-ray structure analyses of It., 17r, 184 and 35 afford geometries in the solid state. Ionization energies are determined by means of photoelectron spectroscopy. The theoretical calculations and interpretation o f absorption spectra and colour are carried out using the models CNDO/S-CI and HAM/3.As a result of both synthetic and spectroscopic studies the nature of vicinal triketones l a or 1 b has been determined').On the other hand, little information has been presented for vinylogous tricarbonyl compounds such as 2, although the spectral properties of this chromophore are important in the interpretation of the colour of violerythrine"), analogous norcarotinoid-dione~~~), and of compounds containing the
The single-crystal X-ray structures of the sulfonium ylides 9,9-dideuteriothioxanthenium bis(carboethoxy)methylide and thioxanthonium bis(carbomethoxy)methylide reveal that both molecules are folded about an imaginary line connecting C(9) and S (138°and 169°, respectively). Like the corresponding sulfoxides, the methylide carbon is pseudoequatorial (e') in both ylides. The malonylide fragment resides in the plane which bisects the "angle of the fold" of the heterocycle. The oxygen of one carbonyl group ("endo") is arrayed essentially trans to the nonbonding electron pair on sulfur. Dimethyl 9-(l,4-dimethylthioxanthenyl)malonate exists with the malonyl fragment in the pseudoaxial (a') position. 13C resonances of a' methylide carbons in these thioxanthenium ylides occur downfield of corresponding e' methylide carbons (67 vs. 54 ppm). The methylide carbons of related thioxanthonium ylides resonate near 60 ppm, reflecting their intermediate geometry. Both *H and 13C NMR spectra indicate a relatively high rotational barrier about the S+-C~bond in bis(carbomethoxy)methylides derived from thioxanthone, 2-chlorothioxanthone, and 2,4-dimethylthioxanthone. Infrared spectra can be used to distinguish isomeric ylides and thioxanthenes. S(10)-C( 12) 1.770 (3) S(10)-C( 13) 1.755 (3) C(l)-C(2) 1.401 (4) C(1)-C(U) 1.410 (3) C(l)-C(15) 1.496 (4) C(2)-C(3)1.366 (4) C(3)-C(4) 1.384 (4) C(4)-C( 12) 1.393 (4) C(4)-C( 16) 1.497 (4) C(5)-C( 13) 1.402 (5) C( 5)-C( 6) 1.368 (5) C( 6)-C( 7) 1.373 (4) C( 7)-C( 8) 1.388 (6) C(8)-C( 14) 1.388 (15) C( 9)-C(ll)1.513(4) C(9)-C( 14) 1.510(5) C(9)-C(17) 1.556(4) C(ll)-C(12) 1.403 (3) C(13)-C(14) 1.385 (3) C(17)-C(18) 1.513(5) C(18)-0(19) 1.201(3) C(18)-O(20) 1.327 (4) O(20)-C(21) 1.436(6) C(17)-C(22) 1.518(4) C(22)-0(23) 1.194(4) C(22)-0(24) 1.322(3) 0(24)-C(25) 1. 440(5) ylide [thioxanthonium bis(carbomethoxy)methylide ( 5)].Recently,6 we prepared thioxanthenium methylides which, because of peri substitution at C(4),2 must exist with the methylide carbon in the a' position. Using these as model compounds, and not making any other assumptions, it was possible to demonstrate that simple ylides of thioxanthene (i.e., those lacking substituents at C(4)/C(5) and C( 9)) exist in the e' conformation. Our 9,9-Dideuteriothioxanthenium Bis(carboethoxy)methylide
The luminescence of benzenoid and naphthalenic compounds is quenched by neighbouring cyclopropyl groups.THE fluorescence yield of (I) (#, = 0,005) is low relative to that of (11) = 0.6).l We report the effect of neighbouring cyclopropyl groups on the luminescence of some aromatic compounds, and show that introduction of a cyclopropyl group near a chromophore which absorbs in the near-u.v. region can result in both fluorescence-and phosphorescence-quenching. The degree of quenching is shown to be dependent on temperature and on the energy and lifetime of the emitting state. The compounds studied will be discussed in pairs ; the fluorescence and phosphorescence yields (#, and #p) of the cyclopropane derivative being compared to those of its open-chain analogue within the framework of the following scheme.? ( 4, ) were observed. At room temperature, in isopentane, 4, for ( 111) is less than a factor of two lower than 4, for (IV).
A new synthesis of cyclobutenedione (1) is described. It is found that the tricyclic cyclobutanedione 3 splits into 1 and cyclopentadiene if subjected to flash pyrolysis conditions. The dienophilic reactivity of 1 allows the construction of various polycyclic cyclobutanediones, such as 3–5 and 12–14. Other new polycyclic diones, like 9–11, 15 and 16 are prepared by means of the acyloin condensation. The low stereoselectivity of 1 with cyclopentadiene is compared with the selectivity of other cyclobutenes, and the results are placed in the context of secondary interactions and steric hindrance. The unusual colour properties of these diones, from colourless 1 to blue 6 are investigated by means of photoelectron spectroscopic measurements and semi‐empirical calculations (MNDO, HAM/3, CNDO/S‐CI).
linear reactivity-selectivity relationship. Since the selectivity scale has to be spread out for the graphical display in Figure 2, minor deviations from the linear reactivity-reactivity relationships lead to noticeable deviations from the ideal linear reactivity-selectivity relationship.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.