Gas‐phase acidity of<i>para</i>‐substituted benzoic acids—a triadic analysis of substituent effects

Vianello, Robert; Maksić, Zvonimir B.

doi:10.1002/poc.921

Cited by 21 publications

(12 citation statements)

References 44 publications

(35 reference statements)

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“…[74] We note in passing that this approach has proved useful in interpreting substituent effects too, as was convincingly shown recently. [75][76][77] As a final remark, it should be mentioned that Koopmans' (IE) n Koop orbital energies were computed using the HF/6-311+G(d,p)//B3LYP/6-31+G(d) model. All the calculations were carried out using the GAUSSIAN03 program.…”

Section: Theoretical Methods and Computational Proceduresmentioning

confidence: 99%

Design of Brønsted Neutral Organic Bases and Superbases by Computational DFT Methods: Cyclic and Polycyclic Quinones and [3]Carbonylradialenes

2007

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The gas‐phase proton affinities and basicities of a large number of extended polycyclic π systems possessing a carbonyl oxygen head serving as a basic proton scavenger are explored by using DFT at the B3LYP/6‐311+G(d,p)//B3LYP/6‐31+G(d) level of theory. Some of these neutral organicsuperbases exhibit proton affinities in the range of 264–284 kcal mol–1. In constructing these systems it turned out that a =C(NMe2)2 fragment attached to a quinoid six‐membered ring enhanced the basicity to a considerable extent. There is abundant and convincing evidence that protonation triggers strong aromatization of the quinoid rings. Moreover, sequential quinoid rings undergo the aromatic domino effect upon protonation if linearly aligned. Triadic analysis has revealed that highly pronounced basicity in some studied systems is a result of the synergistic action of Koopmans' frozen neutral base ionization energy contribution and subsequent relaxation of the radical cation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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Section: Theoretical Methods and Computational Proceduresmentioning

confidence: 99%

Design of Brønsted Neutral Organic Bases and Superbases by Computational DFT Methods: Cyclic and Polycyclic Quinones and [3]Carbonylradialenes

2007

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“…Small sensitivity of BDE to substituent effects was anticipated already by Bordwell et al2; in combination with the rather great experimental uncertainty it makes this quantity quite unsuitable for the studies of substituent effects. In his recent theory Maksić divided the energy of ionization of organic acids into three terms including BDE 24, 25. In the light of the present results, one can understand that in some cases BDE contributes little to the substituent effects because of its small variability;24 however in other cases this term is more variable and important 25…”

Section: Resultsmentioning

confidence: 51%

“…In his recent theory Maksić divided the energy of ionization of organic acids into three terms including BDE 24, 25. In the light of the present results, one can understand that in some cases BDE contributes little to the substituent effects because of its small variability;24 however in other cases this term is more variable and important 25…”

Section: Resultsmentioning

confidence: 51%

Metadata harvesting for content‐based distributed information retrieval

Simeoni

Yakici

Neely

et al. 2007

J. Am. Soc. Inf. Sci.

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We propose an approach to content-based Distributed Information Retrieval based on the periodic and incremental centralization of full-content indices of widely dispersed and autonomously managed document sources. Inspired by the success of the Open Archive Initiative's (OAI) Protocol for metadata harvesting, the approach occupies middle ground between content crawling and distributed retrieval. As in crawling, some data move toward the retrieval process, but it is statistics about the content rather than content itself; this grants more efficient use of network resources and wider scope of application. As in distributed retrieval, some processing is distributed along with the data, but it is indexing rather than retrieval; this reduces the costs of content provision while promoting the simplicity, effectiveness, and responsiveness of retrieval. Overall, we argue that the approach retains the good properties of centralized retrieval without renouncing to costeffective, large-scale resource pooling. We discuss the requirements associated with the approach and identify two strategies to deploy it on top of the OAI infrastructure. In particular, we define a minimal extension of the OAI protocol which supports the coordinated harvesting of full-content indices and descriptive metadata for content resources. Finally, we report on the implementation of a proof-of-concept prototype service for multimodel content-based retrieval of distributed file collections. IntroductionOur interest is in content-based retrieval of widely dispersed and autonomously managed document sources. 1 This is the central problem of Distributed Information Retrieval (DIR), and over the past 10 years, it has been mainly approached by distributing the retrieval process along with the data: Queries have been "pushed" toward the content, and the results of their local execution have been centrally gathered and presented to the user (cf. Callan, 2000a).Traditionally, distributed retrieval services have relied on simple client/server architectures in which brokers route queries submitted by local or remote clients toward a number of mutually autonomous and potentially uncooperative retrieval engines. Figure 1 shows how client/server distributed retrieval works. A Search Broker B interfaces Clients C and dispatches their Queries Q to a number of autonomous search engines. S 1 , S 2 , S n , each of which executes it against an Index FT i of some Content C i before returning Results R i back to B, which merges them and relays them to C. Optionally, B optimizes query distribution by selecting a subset of the engines based on previously gathered descriptions of their content. Based on summary descriptions of the content served by each engine, advanced techniques of source selection and data fusion have been produced to, respectively, minimize network In the lack of a well-established terminology, we use the term contentbased to characterize retrieval processes defined over indices of essentially unstructured documents. Content-based retrieval lies at one...

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“…To make the overview easier, we collected all values, old and new, in Table S1, Supporting Information. Several smaller series were also published in the literature, obtained by DFT or other methods 30–35. The following results are based only on our own calculations.…”

Section: Resultsmentioning

confidence: 99%

Interaction of two functional groups through the benzene ring: Theory and experiment

Böhm

Exner

2008

J Comput Chem

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Energies of 132 benzene para bis-derivatives calculated within the framework of the density functional theory at the level B3LYP/6-311+G(d,p)//B3LYP/6-311+G(d,p) were used for correlations of two types. Correlation with the experimental enthalpies of formation clearly revealed that the published experimental data are generally not dependable and may be loaded with errors of more than 10 kJ mol(-1). On the other hand, the calculated relative energies are biased so that the interaction of the two substituents is systematically overestimated. This shortcoming was insignificant for our correlations of the second type, in which the interaction of substituents expressed in terms of isodesmic reactions was analyzed depending on the effects of inductive and resonance. The results depended strongly on the character of substituents. When one substituent is an electron donor and the other is an acceptor, the inductive-resonance model works and the classical resonance picture is adequate. With two acceptor substituents, this model is still acceptable with lower precision (as crossed conjugation), but with two donors it fails completely and may be acceptable only for a much restricted subclass of strong donors. Many correlations described in the literature must be viewed with great caution when they are based only on a relatively small number of data, in which substituents of different types are not represented in a comparable number.

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Gas‐phase acidity ofpara‐substituted benzoic acids—a triadic analysis of substituent effects

Cited by 21 publications

References 44 publications

Design of Brønsted Neutral Organic Bases and Superbases by Computational DFT Methods: Cyclic and Polycyclic Quinones and [3]Carbonylradialenes

Design of Brønsted Neutral Organic Bases and Superbases by Computational DFT Methods: Cyclic and Polycyclic Quinones and [3]Carbonylradialenes

Metadata harvesting for content‐based distributed information retrieval

Interaction of two functional groups through the benzene ring: Theory and experiment

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