117,299 research outputs found
ChemInform Abstract: Sterically Crowded Cyclohexanes. Part 10. Synthesis, Conformation and Dynamics of 8,8,13,13-Tetramethyltetraspiro(2.0.3.1.3.1.3.0) heptadecane.
No full textChemInform Abstract: Cascade Rearrangements. Part 21. Mono- and Bicyclic Cyclopentenes by Rearrangement of 1-Methylcyclobutylmethanols: Synthesis of (.+-.)-Cuparene and Formal Syntheses of (.+-.)-Laurene and (.+-.)-Herbertene.
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A new approach to helical primary structures of four-membered rings: (P)- and (M)-tetraspiro[3.0.0.0.3.2.2.2]hexadecane
No full textA new approach to helical primary structures of four-membered rings uses a cycloaddition of a trimethylenketeniminium salt to suitable tailored methylenecyclobutanes to assemble the desired carbon framework. The results are short and effective syntheses of (M)-trispiro[3.0.0.3.2.2]tridecane [(M-5], and (P)- and (M)-tetraspiro[3.0.0.0.3.2.2.2]hexadecane [(P)- and (M)-24]. Unlike helices of three-membered rings, the specific rotation decreases, as the length of the helix increases. (C) 2003 Elsevier Ltd. All rights reserved
Cascade rearrangements, part 24. Synthesis and rearrangement of [1,1 '-bicyclobutyl]-1-ols and spiro[3.4]octan-5-ols: a general access to bicyclo[3.3.0]octenes (hexahydropentalenes)
No full textSeveral new Grignard reagents based on substituted cyclobutanes have been generated and added to cyclobutanones to yield mono- to trimethylated [1,1'-bicyclobutyl]-1-ols. Mono- to trimethylated spiro[3.4]octan-5-ols have been prepared from the parent ketone via alkylation and/or addition reactions. Upon treatment with acid, all [1,1'-bicyclobutyl]- 1 -ols and spiro[3.4]octan-5-ols rearrange to yield a single bicyclo[3.3.0]octene. (C) 2004 Elsevier Ltd. All rights reserved
ChemInform Abstract: Cascade Rearrangements. Part 22. The Bicyclobutylidene to Bicyclooctene Rearrangement: Formal Syntheses of (.+-.)-Ceratopicanol and (.+-.)-Hirsutene.
No full textHelical primary structures of four-membered rings: (M)-trispiro[3.0.0.3.2.2]tridecane
No full textThe synthesis of (NI)-trispiro[3.0.0.3.2.2]tridecane [(M)-4], the first hydrocarbon with a helical primary structure of four-membered rings, is described. Key step is the kinetic resolution of a cyclobutanone through reduction with bakers' yeast. As compared to its analogue of three-membered rings, (M)-trispiro[2.0.0.2.1.1]nonane [(M)-1], the specific rotation of (M)-4 is cut in three. According to molecular mechanics calculations this could be due to a potential to adopt different conformations, not given in (M)-1, and to the fact, that (M)-4 describes a distinctly shorter section of a helix than (M)-1. (C) 2003 Elsevier Science Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Square Dancing with the Stars to Enhance Dynamic Hirschman Linkages?
No full textIn this Presidential Address, the author takes the reader on a reconnaissance of his life and time as a regional scientist. He points out scenery he found scintillating along the way, hoping that some may pick up the banner and chew on a few of the ideas for a while. He suggests a revisit to Albert O. Hirschman’s notion of key sectors and more empirical analysis related to Marcus Berliant’s and Masahisa Fujita’s notion of knowledge creation and transfer.Presidential Address, San Antonio, Texas, March 29, 2014 (53rd Meetings of the Southern Regional Science Association
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe 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
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