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Related Concept Videos

SN1 Reaction: Stereochemistry02:15

SN1 Reaction: Stereochemistry

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This lesson provides an in-depth discussion of the stereochemical outcomes in an SN1 reaction.
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
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SN1 Reaction: Kinetics02:05

SN1 Reaction: Kinetics

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In an SN2 reaction, the reaction rate depends on both the type of nucleophile and the substrate. A hindered tertiary alkyl halide is practically inert to the SN2 mechanism despite using a strong nucleophile.
However, Sir Christopher Ingold and Edward D. Hughes, who studied the kinetics of various nucleophilic substitution reactions, noticed that a tertiary alkyl halide does undergo a nucleophilic substitution reaction in the presence of a weak nucleophile. While studying the substitution...
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SN1 Reaction: Mechanism02:25

SN1 Reaction: Mechanism

14.5K
Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism. 
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a...
14.5K
Acidity of 1-Alkynes02:42

Acidity of 1-Alkynes

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The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
11.3K
Predicting Products: SN1 vs. SN202:27

Predicting Products: SN1 vs. SN2

17.4K
Nucleophilic substitution reactions of alkyl halides can proceed via an SN1 or an SN2 mechanism. While in SN2 reactions, the nucleophile attacks the substrate simultaneously as the leaving group departs, in SN1 reactions, the substrate first dissociates to give the carbocation intermediate. Various factors such as the structure of the substrate, the strength of the nucleophile, and the nature of the solvent promote one mechanism over the other.
With increased substitution on the alkyl halide,...
17.4K
Preparation of 1° Amines: Gabriel Synthesis01:28

Preparation of 1° Amines: Gabriel Synthesis

4.7K
Direct alkylation is not a suitable method for synthesizing amines because it produces polyalkylated products. Gabriel synthesis is the most preferred method to exclusively make primary amines. The method uses phthalimide, which contains a protected form of nitrogen that participates in alkylation only once to predominantly give primary amines.
Strong bases like NaOH or KOH deprotonate the phthalimide to form the corresponding anion, which acts as a nucleophile. Further, the anion attacks an...
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Are you in top 1% (1‰)?

Marek Kosmulski1

  • 1Lublin University of Technology, Lublin, Poland.

Scientometrics
|February 17, 2018
PubMed
Summary
This summary is machine-generated.

A novel bibliometric indicator uses highly cited papers to evaluate researchers, journals, and universities. This method offers a fair assessment for early-career scientists and those in less popular fields, differing from traditional citation metrics.

Keywords:
Assessment of authorsAssessment of publicationsCitationScientific degree

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Area of Science:

  • Bibliometrics
  • Scientometrics
  • Research Evaluation

Background:

  • Traditional citation-based indicators may disadvantage early-career researchers and those in less-popular disciplines.
  • Existing metrics like citation counts and the Hirsch-index (h-index) have limitations in providing equitable research assessments.

Purpose of the Study:

  • To introduce and validate a new, simple bibliometric indicator based on the number of highly cited papers.
  • To assess the suitability of this indicator for evaluating individuals, journals, and universities.
  • To compare the proposed indicator's ranking with existing metrics like citation counts and the h-index.

Main Methods:

  • Defining 'highly cited papers' using a recognized database (e.g., Web of Science).
  • Calculating the new indicator based on the count of these highly cited papers for different entities (individuals, journals, universities).
  • Correlating the rankings derived from the new indicator with those from traditional metrics.

Main Results:

  • The new indicator provides a simple yet effective method for research assessment.
  • It equalizes opportunities for young scientists and researchers in less-popular fields.
  • Rankings from this indicator show no correlation with rankings based on total citations or the h-index.

Conclusions:

  • This highly cited paper indicator offers a more equitable approach to research evaluation.
  • It serves as a valuable tool for assessing individuals, journals, and institutions.
  • The indicator's independence from traditional metrics suggests it captures different aspects of research impact.