1,720,967 research outputs found
Fotolisi di 4,4’ dimetossidifenilmetano sensibilizzata da benzochinoni in acetonitrile. Effetto della struttura del sensibilizzatore nella competizione tra rottura omolitica ed eterolitica del legame C-H nel radicale catione
No full textPhotoinduced Reduction of Chloranyl with Alkyl- and Thio-aromatics Investigated by Laser Flash Photolysis
No full textAerobic Oxidation of Benzyl Alcohols Catalyzed by Aryl Substituted N-Hydroxyphthalimides. Possible Involvement of a Charge-Transfer Complex.
No full textPhotosensitized Oxidation of Alkyl Phenyl Sulfoxides. C-S Bond Cleavage in Alkyl Phenyl Sulfoxide Radical Cations
No full textThe 3-cyano-N-methylquinolinium perchlorate (3-CN-NMQ+ ClO4
-)-photosensitized oxidation of phenyl alkyl
sulfoxides (PhSOCR1R2R3, 1, R1 ) R2 ) H, R3 ) Ph; 2, R1 ) H, R2 ) Me, R3 ) Ph; 3, R1 ) R2 ) Ph, R3
) H; 4, R1 ) R2 ) Me, R3 ) Ph; 5, R1 ) R2 ) R3 ) Me) has been investigated by steady-state irradiation
and nanosecond laser flash photolysis (LFP) under nitrogen in MeCN. Steady-state photolysis showed the
formation of products deriving from the heterolytic C-S bond cleavage in the sulfoxide radical cations (alcohols,
R1R2R3COH, and acetamides, R1R2R3CNHCOCH3) accompanied by sulfur-containing products (phenyl
benzenethiosulfinate, diphenyl disulfide, and phenyl benzenethiosulfonate). By laser irradiation, the formation
of 3-CN-NMQ• (λmax ) 390 nm) and sulfoxide radical cations 1•+, 2•+, and 5•+ (λmax ) 550 nm) was observed
within the laser pulse. The radical cations decayed by first-order kinetics with a process attributable to the
heterolytic C-S bond cleavage leading to the sulfinyl radical and an alkyl carbocation. The radical cations
3•+ and 4•+ fragment too rapidly, decaying within the laser pulse. The absorption band of the cation Ph2CH+
(λmax ) 440 nm) was observed with 3 while the absorption bands of 3-CN-NMQ• and PhSO• (λmax ) 460
nm) were observed just after the laser pulse in the LFP experiment with 4. No competitive -C-H bond
cleavage has been observed in the radical cations from 1-3. The C-S bond cleavage rates were measured
for 1•+, 2•+, and 5•+. For 3•+ and 4•+, only a lower limit (ca. >3 × 107 s-1) could be given. Quantum yields
(Φ) and fragmentation first-order rate constants (k) appear to depend on the structure of the alkyl group and
on the bond dissociation free energy (BDFE) of the C-S bond of the radical cations determined by a
thermochemical cycle using the C-S BDEs for the neutral sulfoxides 1-5 obtained by DFT calculations.
Namely, Φ and k increase as the C-S BDFE becomes more negative, that is in the order 1 < 5 < 2 < 3, 4,
which is also the stability order of the alkyl carbocations formed in the cleavage. An estimate of the difference
in the C-S bond cleavage rate between sulfoxide and sulfide radical cations was possible by comparing the
fragmentation rate of 5•+ (1.4 × 106 s-1) with the upper limit (104 s-1) given for tert-butyl phenyl sulfide
radical cation (Baciocchi, E.; Del Giacco, T.; Gerini, M. F.; Lanzalunga, O. Org. Lett. 2006, 8, 641-644). It
turns out that sulfoxide radical cations undergo C-S bond breaking at a rate at least 2 orders of magnitude
faster than that of corresponding sulfide radical cations
Competition BetweenCα-S and Cα-Cβ Bond Cleavage in β-Hydroxy Sulfoxide and Phenylsulfinylacetic Acid Radical Cations
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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