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21.
Ivan Gutman 《Monatshefte für Chemie / Chemical Monthly》2005,136(6):1055-1069
Summary. The fact that cyclic arrangements of double bonds have a dramatic effect on the behavior of conjugated organic molecules is known since the 19th century. The fact that in monocyclic conjugated systems the size of the cycle and the number of -electrons involved is decisive for their stability (aromaticity) or lack of stability (antiaromaticity) is known since the 1930s. In polycyclic -electron systems several cyclic effects are present simultaneously and their separation became possible only recently. A molecular orbital method has been elaborated, by means of which the energy effects of individual cycles in polycyclic -electron systems can be estimated. This method is briefly outlined and illustrated by pertinent examples. An exhaustive bibliography of the topic considered is given. 相似文献
22.
5,6-Bis(dimethylamino)acenaphthylene is readily involved in [4+2] cycloaddition reactions with symm-tetrazine derivatives to form new proton sponges with the diazafluoranthene skeleton. Under analogous condition, 1,8-bis(dimethylamino)-4-vinylnaphthalene gave 4-pyridazinyl derivatives. The relative reactivities of 5,6-bis(dimethylamino)acenaphthylene, 1,8-bis(dimethylamino)-4-vinylnaphthalene, 5-dimethylaminoacenaphthylene, and acenaphthylene in the reactions with 3,6-diphenyl-symm-tetrazine are in a ratio of 32 : 17 : 14 : 1. The site of protonation of 3,4-bis(dimethylamino)-7,10-diphenyl-8,9-diazafluoranthene is controlled by the basicity of the solvent. The reaction in acetonitrile afforded the cation stabilized by an intramolecular hydrogen bond, whereas the reaction in dimethyl sulfoxide gave rise to the resonance-stabilized cation. 6,7-Bis(dimethylamino)phenalen-1-one was protonated only at the carbonyl group. 相似文献
23.
The kinetics of electroreduction of Pd(II) complexes with -alanine, Pd(ala)2, is studied on a rotating Pd disk electrode in solutions of pH 8–13 containing large excess of -alanine and various supporting electrolytes (NaF, Na2SO4, NaClO4). On a Pd electrode, complexes Pd(ala)2 undergo reduction at potentials much more negative than on an Hg electrode. This is attributed to the chemisorption of water on the Pd electrode, which hampers adsorption of Pd(ala)2 that take part in the slow electrochemical stage. As with the Hg electrode, perchlorate ions hinder the Pd(ala)2 reduction on a Pd electrode. Studying adsorption of Pd(ala)2 on a Pd electrode is hampered by parallel processes of hydrogen adsorption and absorption. 相似文献
24.
Concurrent solvent evaporation with a loop-type interface was used for on-line HPLC-CGC in the analysis of methylated dibenzothiophene (DBT) isomers in oil samples. The chromatographic behavior of 20 methyl DBT's was studied by HPLC on an aminopropylsilane DBTA phase and by GC on a selective methyl-phenylsilicone phase. That provided a method for analyzing by GC-flame photometric detection, the individual components of the DBT family, previously picked out of the crude oil matrix by HPLC. The GC oven temperature was shown to be critical during HPLC eluent introduction into the GC pre-column. Too high a temperature induced a severe broadening of early eluted peaks whereas a temperature too close to the boiling point of the liquid at the inlet pressure induced double peaks. Optimized conditions were retained on this basis and may be used for the analysis of other families of polyaromatic hydrocarbons. 相似文献
25.
Abdul -Latif K. Al-Jiburi Kisma H. Al-Niami Muthana Shanshal 《Theoretical chemistry accounts》1979,53(4):327-335
The harmonic force constants, vibrational frequencies and integrated intensity ratios of CH2, H2O, CH2O, C2H2, CO2, HCN, CH3, CH4, and C2H4 have been calculated using the MINDO—FORCES program and the Pulay method for the calculation of the molecular force constants. The results obtained are in general quite satisfactory when compared with available literature values. The results are, however, not as satisfactory in case of molecules containing heteroatoms, due to the neglect of some dipolar repulsion integrals for the heteroatoms by the MINDO/3 method. Calculated integrated intensities for CH3 and C2H4 agree well with experimental results. The calculated integrated intensities for other molecules are obtained for the first time and no comparison with published data is therefore possible.Part of the M.Sc. Thesis of K. H. A. 1978. 相似文献
26.
27.
Mohammed Akhter Hossain Keiko Takahashi Hisakazu Mihara Akihiko Ueno 《Journal of inclusion phenomena and macrocyclic chemistry》2002,43(3-4):271-277
-Helix peptides bearing one unit of -cyclodextrin (-CD), one unit of pyrene and one unit of nitrobenzene (NB) in their side chains have been designed and synthesized as novel molecule-responsive devices.In both the CD-peptides,
-PR17 and
-PL17, the NB unit is separated from the CD unit by two turns of the helix. Two reference peptides (PL17, and -P17,) have also been synthesized. The circular dichroism studies in the peptide absorption region (200–250 nm)of
-PR17 and
-PL17 suggestthat the CD-peptides form stable-helixstructures (83–77%), which was destabilized by accommodating guest molecules (e.g., n-pentanol) into the CD cavity. It suggests that formation of intramolecular host–guest(CD–NB) complex stabilized thehelical structure and exogenous guest molecule excluded the appending NB moiety from inside to outside of the CD cavity, thereby causing destabilization of the helical structure and increasing the random coil content. The ICD spectra of the peptides in the pyrene and nitrobenzene absorption region (250–40 nm) suggest that NB forms inclusion complex with CD. The fluorescence studies revealed that the fluorescence of the pyrene unit is quenched by the NB unit in
-PR17 and
-PL17. The fluorescence intensity increases with increasing guest concentration for the CD-peptides.This guest-responsiveenhancement in the fluorescence intensity can be explained in terms of increased distance between the pyrene and NB moieties, which is caused by exclusion of the NB moiety from the CD cavity by guest accommodation. Using the guest-responsive fluorescence quenching properties of the CD-peptides, we have obtained binding constants for various short chain alkanols.
-PL17 has higher binding affinity to the guest molecules than its isomer,
-PR17, indicating that the location of functional groups on the peptide scaffold is important in molecule detection. 相似文献
28.
Barbara Szafran Jan Pawlaczyk 《Journal of inclusion phenomena and macrocyclic chemistry》1995,23(4):277-288
The 1 : 1 inclusion complex involving sulfafurazole (SF) and-cyclodextrin (-CD) is prepared by the freeze-drying method and characterized on the basis of its chemical analysis, thermal behavior, infrared spectrum, X-ray powder pattern and13C NMR spectrum in DMSO-d6 solution. The stability constant of the inclusion complex was determined by the solubility method. The effect of cyclodextrin on the UV absorption spectrum of sulfafurazole was also observed. 相似文献
29.
A. R. Burilov D. V. Cherepachkin I. L. Nikolaeva M. A. Pudovik 《Russian Chemical Bulletin》1995,44(2):345-349
Some newS-phosphorylated,S-silylated, andS-stannylated derivatives of -mercaptoketones were obtained. The reactions of some of these compounds induced by the temperature and by molecular oxygen as well as the phosphorylation of the Si- and Sn-containing derivatives were studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 353–357, February, 1995. 相似文献
30.
L. I. Zakharkin I. M. Churilova G. N. Antonova P. V. Petrovskii N. S. Ikonnikov 《Russian Chemical Bulletin》1994,43(8):1360-1362
Alkylation of cyclododecanone with ,-dibromoalkanes Br(CH)
n
Br (n=3, 4, 5) under conditions of phase-transfer catalysis in the presence of KOH results in the formation of either bicyclic ketones forn=3 and 5 or a mixture of bicyclic and spirocyclic ketones forn=4.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1436–1438, August, 1994. 相似文献