The Response of Electrons to Structural Changes

Wiberg, Kenneth B.; Hadad, Christopher M.; Breneman, Curt M.; Laidig, Keith E.; Murcko, Mark A.; LePage, Teresa J.

doi:10.1126/science.252.5010.1266

Cited by 68 publications

(48 citation statements)

References 46 publications

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“…Kinetic parameters of rotaxanes with tetralactam wheels in comparison with those with sulfonamide wheels Furthermore, comparison of Rot3@2 and Rot4@2, studied under the same conditions, led us to the conclusion that hydrogen bonding does not play a significant role. Fourthly, rotational barriers (Scheme 6) in carbonamides have been studied intensely both experimentally [25] and theoretically [26] and are of the order of 80 kJ/mol, while those of sulfonamides have been calculated to amount to ca. 40 kJ/ mol.…”

Section: Tetralactam Wheel Versus Sulfonamide Macrocyclementioning

confidence: 99%

Rotaxane or Pseudorotaxane? Effects of Small Structural Variations on the Deslipping Kinetics of Rotaxanes with Stopper Groups of Intermediate Size

et al. 2001

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Three series of rotaxanes have been synthesized variously by slipping synthesis, in which axis and wheel are melted in admixture, by recognition of amide groups inside the macrocyclic wheel, or by an anionic template method, in which the stoppering phenolates are hydrogen bonded to the wheel and then joined by reaction with a semi‐axle. The 3,5‐di‐tert‐butylphenyl stopper used for most of these rotaxanes is large enough to permit their isolation, but still allows the wheel to deslip from the axle under appropriate conditions. The deslipping activation parameters for all rotaxanes are derived from 1H NMR kinetic measurements and have been evaluated from the Arrhenius equation as well as according to Eyring theory. Small structural variations give rise to surprising effects on the activation parameters. Firstly, in some examples, the axle length affects the deslipping barrier, although the size complementarity of stopper and wheel remain unchanged. Secondly, stopper flexibility has an important influence on the deslipping rate. Thirdly, exchange of a carbonamide for a sulfonamide in the wheel significantly reduces the entropic costs of the deslipping, resulting in a pronounced deslipping rate enhancement. Fourthly, intramolecular hydrogen bonding within the wheel decelerates deslipping by a factor of more than 104.

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Section: Tetralactam Wheel Versus Sulfonamide Macrocyclementioning

confidence: 99%

Rotaxane or Pseudorotaxane? Effects of Small Structural Variations on the Deslipping Kinetics of Rotaxanes with Stopper Groups of Intermediate Size

et al. 2001

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“…21). It has long been recognized that, due to the presence of electron lone pairs, polarization effects, and so on, the partial atomic charges obtained from different schemes can neither be thought as point charges [22] nor should the charges be considered to be uniformly distributed over atomic spheres. Over the past several years, studies of ESP surfaces have revealed many instances of positive regions falling within otherwise negative regions on the exposed potential surface maps [23].…”

Section: Introductionmentioning

confidence: 99%

Charge competition in halogenated hydrocarbons

Gross¹,

Hadad²,

Seybold³

2011

Int J of Quantum Chemistry

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ABSTRACT:The distribution of electronic charge in a molecule plays a major role in determining the molecule's physical, chemical, and biological properties. For studies of charge distributions, halogenated hydrocarbons are especially informative prototype systems, because the overall charge distributions depend strongly on both the identities and relative positions of the halogen substituents. In this report, we examine how the placement and identities of the halogen substituents affect the natural population analysis, atoms in molecules, and Gasteiger partial atomic charge distributions in representative saturated (methanes and ethanes), unsaturated (ethylenes), and aromatic (benzenes) halogenated hydrocarbons, using density functional calculations. The results are interpreted in terms of the electronegativities and the charge capacities of the halogens. The relationships of these charge distributions to the electrostatic potential maps of the compounds are also explored.

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“…In support of this reevaluation of resonance effects, recent calculational investigations have shown that only a small portion of allylic resonance energy can be attributed to charge delocalization [8]. This result does not imply that electron density and its associated kinetic energy does Anti Enaminonitrile TS not migrate from atom to atom during the course of a conformational change, but rather that the pathways involved in such charge and energy flow are often not those associated with canonical resonance forms.…”

Section: Introductionmentioning

confidence: 81%

The rotational barrier of an enaminonitrile. Charge and energy redistribution during rotation about the C-N bond

Breneman

Moore

1997

Struct Chem

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Ab initio quantum mechanical techniques were used together with PROAIM electron density partitioning and CHELPG electrostatic potential analysis to examine the charge density distribution of model enaminonitrile I in its planar ground state and in its two rotational transition states. The barrier to rotation about the C--N bond was calculated to be 15.4 and 15.6 kcal/mole for the two rotational transition states at the HF/6-31G** level of theory, and was found to originate from a redistribution of electronic kinetic energy between the amino group and the rest of the molecule in a manner similar to that found for formamide and sulfonamide. Similarly, the C--N bond length and amino group electron population were found to depend upon the C--N torsional angle. Electrostatically derived atomic point charges were also examined at each stationary point using the CHELPG program. CHELPG electrostatic potential results were found to represent the traditional "external" viewpoint of the charge density consistent with a resonance model, while the results from PROAIM calculations were found to describe the underlying charge density and kinetic energy density redistribution responsible for the rotational barrier.

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The Response of Electrons to Structural Changes

Cited by 68 publications

References 46 publications

Rotaxane or Pseudorotaxane? Effects of Small Structural Variations on the Deslipping Kinetics of Rotaxanes with Stopper Groups of Intermediate Size

Rotaxane or Pseudorotaxane? Effects of Small Structural Variations on the Deslipping Kinetics of Rotaxanes with Stopper Groups of Intermediate Size

Charge competition in halogenated hydrocarbons

The rotational barrier of an enaminonitrile. Charge and energy redistribution during rotation about the C-N bond

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