STEREOCHEMISTRY OF INCIPIENT ELECTROPHILIC AND NUCLEOPHILIC REACTIONS AT DIVALENT SELENIUM CENTER: ELECTROPHILIC-NUCLEOPHILIC PAIRING AND ANISOTROPIC SHAPE OF Se IN Se…Se INTERACTIONS

Ramasubbu, Narayanan; Parthasarathy, R.

doi:10.1080/03086648708080641

Cited by 68 publications

(63 citation statements)

References 9 publications

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“…This has been demonstrated for covalentlybonded atoms of Group VI [35], Group V [36], and Group IV [37]. This is again caused by the anisotropic charge distributions of the atoms [21,25,38,39], which result in σ-holes on the extensions of single (and sometimes multiple) bonds to these atoms. Accordingly Group VI, V, and IV atoms can have two, three, and four σ-holes, respectively (or more if the atoms are hypervalent [37,40]).…”

Section: The σ-Hole: Halogensmentioning

confidence: 86%

σ-Hole Bonding: A Physical Interpretation

Politzer

Murray

Clark

2014

Topics in Current Chemistry

150

117

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The anisotropic electronic densities of covalently-bonded Group IV-VII atoms frequently give rise to regions of positive electrostatic potential on the extensions of covalent bonds to these atoms. Through such positive "σ-holes," the atoms can interact attractively and highly directionally with negative sites such as the lone pairs of Lewis bases, anions, π electrons, etc. In the case of Group VII this is called "halogen bonding." Hydrogen bonding can be viewed as a less directional subset of σ-hole interactions. Since positive σ-holes often exist in conjunction with regions of negative potential, the atoms can also interact favorably with positive sites. In accordance with the Hellmann-Feynman theorem, all of these interactions are purely Coulombic in nature (which encompasses polarization and dispersion). The strength of σ-hole bonding increases with the magnitudes of the potentials of the positive σ-hole and the negative site; their polarizabilities must sometimes also be taken explicitly into account.

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Section: The σ-Hole: Halogensmentioning

confidence: 86%

σ-Hole Bonding: A Physical Interpretation

Politzer

Murray

Clark

2014

Topics in Current Chemistry

150

117

View full text Add to dashboard Cite

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“…It is not only covalently-bonded halogens that have lower electronic densities (σ-holes) on the extensions of their bonds; this is true as well of covalently-bonded atoms in other Groups of the periodic table [12,[35][36][37][38]40]. In the years 2007-2009, positive σ-hole potentials were found for atoms in Groups VI [41], V [42], and IV [43].…”

mentioning

confidence: 90%

“…One is that van der Waals radii are typically based upon the assumption that the atoms, despite being covalently bonded, are spherical. It is well known that this is not true [12,[35][36][37][38][39][40]; σ-holes are in fact a manifestation of the asymmetry of covalently-bonded atoms, which can be quite substantial. From analyses of crystal data, Nyburg and Faerman estimated the radii of chlorines bonded to carbons to be, on the average, 0.2 Å shorter along the extensions of the bonds than perpendicular to them [36]; for sulfurs doubly-bonded to carbons, they found a difference of 0.4 Å. Eramian et al predict somewhat smaller but still significant asymmetries [40].…”

Section: Van Der Waals Radii and Close Contactsmentioning

confidence: 99%

“…However, they were not What is the origin of such positive potentials on electronegative atoms? It has been known for quite some time that atoms involved in covalent single (and sometimes double) bonds have lesser electronic densities (and shorter radii) on the extensions of the bonds than on their lateral sides [12,26,27,[35][36][37][38][39][40]. This has sometimes been called "polar flattening".…”

mentioning

confidence: 99%

“…Just as for the halogens, these positive regions can interact attractively with negative sites, and thus account for noncovalent interactions involving Groups IV−VI that have been known experimentally (and later computationally) for many years [35,37,[44][45][46][47][48][49]. However, they were not What is the origin of such positive potentials on electronegative atoms?…”

mentioning

confidence: 99%

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σ-Hole Interactions: Perspectives and Misconceptions

2017

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After a brief discussion of the σ-hole concept and the significance of molecular electrostatic potentials in noncovalent interactions, we draw attention to some common misconceptions that are encountered in that context: (1) Since the electrostatic potential reflects the contributions of both the nuclei and the electrons, it cannot be assumed that negative potentials correspond to "electron-rich" regions and positive potentials to "electron-poor" ones; (2) The electrostatic potential in a given region is determined not only by the electrons and nuclei in that region, but also by those in other portions of the molecule, especially neighboring ones; (3) A σ-hole is a region of lower electronic density on the extension of a covalent bond, not an electrostatic potential; (4) Noncovalent interactions are between positive and negative regions, which are not necessarily associated with specific atoms, so that "close contacts" between atoms do not always indicate the actual interactions.Keywords: σ-holes; noncovalent interactions; electrostatic potential; close contacts A Brief History of the σ-HoleThe σ-hole concept was introduced by Clark in the context of halogen bonding, at a conference in 2005 [1], although it did not appear in the chemical literature until 2007 [2]. Halogen bonding involves a favorable noncovalent interaction between a covalently-bonded halogen and a negative site, such as a lone pair. Such interactions were already known to experimentalists in the 19th century [3,4], and were studied extensively in the 20th [5][6][7][8][9][10], with crystallography playing a major role [10][11][12][13]. Nevertheless the basis for halogen bonding was not really understood. It was frequently rationalized as "charge transfer" from an electron "donor" (e.g., the lone pair) to an "acceptor" (the halogen), invoking the valence bond formalism of Mulliken [14] (which was later put in molecular orbital terms by Flurry [15,16]).However, the halogen is the most electronegative atom in each row of the periodic table, and a singly-bonded halogen atom is generally viewed as being negative in character. So why should it interact attractively with a donor of electronic charge? It was in fact pointed out long ago [7,17] that Mulliken's charge-transfer formalism was not intended to be an elucidation of the bonding in a ground-state noncovalent complex; it was purely a mathematical modeling of the transition of the ground-state complex to a low-lying excited state. The existence of halogen bonding was thus viewed by many as an enigma.The key to resolving the enigma was the molecular electrostatic potential. This is the potential V(r) that is created at any point r in the space of a molecule by its nuclei and electrons, given rigorously by Equation (1):Z A is the charge on nucleus A, located at R A , and ρ(r) is the molecule's electronic density. Regions in which V(r) is positive, indicating the dominance of the nuclear contribution, are attractive to

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Structure of 1-(Arylselanyl)naphthalenes − Y Dependence in 1-(p-YC6H4Se)C10H7

2001

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Keywords: Biaryl compounds / Selenium / Through-bond interactions / Substituent effectsThe structures of 1-(arylselanyl)naphthalenes [1-(p-YC 6 H 4 -Se)C 10 H 7 (1), where Y = H (a), OMe (b), Me (c), Cl (d), Br (e), COOEt (f), and NO 2 (g)] were determined. The structures of 1 were well classified using types A, B, and C, where the Se−C Ar bond in 1 is placed almost perpendicular to the naphthyl plane in type A and is located on the plane in type B. The type C structure is intermediate between type A and type B. The structures of 1d−1f are demonstrated to be type A whereas that of 1b is type B by X-ray crystallographic analysis. The type B conformer is suggested to be favorable in solutions for 1a and 1c based on the NMR-spectroscopic data. The structure of 1g is assumed to be type A. These results show that the stable structure of 1 must be type A or type B, contrary to early observations of type C for 1,8-bis(alkyl-or arylchalcogeno)naphthalenes. Consequently, the structure of 1 changes dramatically depending on Y in the solid state. We propose that these structures can be explained by the electron affinities, together with the energies of LUMO and

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STEREOCHEMISTRY OF INCIPIENT ELECTROPHILIC AND NUCLEOPHILIC REACTIONS AT DIVALENT SELENIUM CENTER: ELECTROPHILIC-NUCLEOPHILIC PAIRING AND ANISOTROPIC SHAPE OF Se IN Se…Se INTERACTIONS

Cited by 68 publications

References 9 publications

σ-Hole Bonding: A Physical Interpretation

σ-Hole Bonding: A Physical Interpretation

σ-Hole Interactions: Perspectives and Misconceptions

Structure of 1-(Arylselanyl)naphthalenes − Y Dependence in 1-(p-YC6H4Se)C10H7

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