Localized charge distributions. I. General theory, energy partitioning, and the internal rotation barrier in ethane

England, Walter B.; Gordon, Mark S.

doi:10.1021/ja00748a002

Cited by 106 publications

(30 citation statements)

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“…Although the key paper under consideration is a convincing validation of the hypothesis that hyperconjugation controls the ethane barrier, this idea is by no means new. As already noted above, Mulliken appears to have been the first to propose this possibility in 1939,20 and there was a continuous flow of publications that utilized increasingly sophisticated studies of this attractive idea, especially those of Lowe,34–36 England and Gordon,37 as well as Brunck, Weinhold, and Reed 2, 19, 38. The Pophristic and Goodman paper re‐emphasizes, by analyzing in detail a straightforward yet intricate problem, that chemistry often is not as easy as we hope it to be and as we would like to teach it.…”

Section: Methodsmentioning

confidence: 95%

Teaching the Right Reasons: Lessons from the Mistaken Origin of the Rotational Barrier in Ethane

Schreiner

2002

Angew. Chem. Int. Ed.

113

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when will chemistry textbooks begin to serve as aids, rather than barriers, to this enriched quantum-mechanical perspective... F. Weinhold (2001) When I was first properly introduced to chemistry in the 9th grade, electrons (™chemical glue∫) were simply described as single dots around atoms. Magically, sharing the dots meant a ™chemical bond∫ and one had only to count up to eight to figure out how many electrons were shared and how many bonds you would have. Easy. We counted ions, balanced redox reactions, and had fun with oxidation numbers for inorganic and simple organic species. Then things became more complicated. We were introduced to Bohr×s model, in which you could only have two electrons in the innermost shell and eight in the next; beyond that, who knows what. That all had to do with some complicated quantum theory that we could not possibly understand in detail, so we were asked just to accept it. We did, until two years later when suddenly we were told that Bohr×s model is really too much of an approximation and that chemical bonding is far more complicated. It should be expressed using the intricate laws of quantum mechanics, namely, in terms of molecular orbitals. All bond types (multiple, metallic, back-bonding, etc.) suddenly became unique and things were really complicated mathematically. I remember well the funny-looking dumbbell-shaped, colorful styrofoam models of the various d orbitals, and thought that nature could not possibly be that complicated; in any case, two years from then they would tell us otherwise anyway. So I decided not to accept anything that had to do with this awkward quantum theory, only to be quizzed in the next class session. Needless to say, I received the worst grade in my chemical life and was embarrassed in front of the entire class. Shortly thereafter I decided to become a chemist.The reason that I am telling this story is because there are, as always, two sides to it. Teachers, on the one hand, can confuse and frustrate their students by trying to depict chemistry in the most up-to-date, albeit complicated fashion. On the other hand, motivated students will despise simple models if more appropriate ones continually replace them. Frustration may be the final result. The simplification approach may be acceptable at the high school level because easily understandable explanations, although possibly inadequate, do get the message across. At higher scholastic levels, however, this is no longer acceptable because we owe it to the students to teach them our current knowledge and interpretation of science. The convenience of visually pleasing explanations for intricate chemical phenomena must not outweigh proper physical descriptions. These are available through modern quantum mechanics within the Born ± Oppenheimer approximation that allows approximate solutions of the electronic Schrˆdinger equation in the form of potential energy hypersurfaces. Hence, quantum mechanics provides us with an accurate theoretical description. The subsequent interpretation is a model that may ...

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Section: Methodsmentioning

confidence: 95%

Teaching the Right Reasons: Lessons from the Mistaken Origin of the Rotational Barrier in Ethane

Schreiner

2002

Angew. Chem. Int. Ed.

113

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“…We have reinvestigated the rotation around the C À C bond in ethane employing a widely used and straightforward electronic-structure analysis method (see below). It turns out that it is very important to take carefully into account the effect of geometry changes during rotation around the CÀC bond, notably the CÀC bond stretching when going towards the eclipsed conformation, as indeed already stressed by England and Gordon [14] and Goodman and coworkers. [15] We will see that the interpretation of the barrier as caused by steric repulsion between vicinal C À H bonds is fully corroborated by this analysis, and we conclude it is perfectly valid for organic chemists to adhere to this view.…”

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confidence: 91%

The Case for Steric Repulsion Causing the Staggered Conformation of Ethane

2003

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“…We have reinvestigated the rotation around the CC bond in ethane employing a widely used and straightforward electronic‐structure analysis method (see below). It turns out that it is very important to take carefully into account the effect of geometry changes during rotation around the CC bond, notably the CC bond stretching when going towards the eclipsed conformation, as indeed already stressed by England and Gordon14 and Goodman and co‐workers 15. We will see that the interpretation of the barrier as caused by steric repulsion between vicinal CH bonds is fully corroborated by this analysis, and we conclude it is perfectly valid for organic chemists to adhere to this view.…”

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confidence: 93%

The Case for Steric Repulsion Causing the Staggered Conformation of Ethane

Bickelhaupt

Baerends

2003

Angewandte Chemie

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Die Rotationsbarriere in Ethan (siehe Bild) gilt als prototypisches Beispiel für sterische Hinderung. Dem wurde kürzlich widersprochen: Stattdessen wurde Hyperkonjugation als zutreffende Begründung vorgebracht. Nach Ansicht der Autoren gibt es keinen Grund, die Erklärung durch sterische Abstoßung zu verlassen. Sie zeigen, warum unterschiedliche Analysen der elektronischen Struktur zu unterschiedlichen Ergebnissen führen.

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Localized charge distributions. I. General theory, energy partitioning, and the internal rotation barrier in ethane

Cited by 106 publications

References 0 publications

Teaching the Right Reasons: Lessons from the Mistaken Origin of the Rotational Barrier in Ethane

Teaching the Right Reasons: Lessons from the Mistaken Origin of the Rotational Barrier in Ethane

The Case for Steric Repulsion Causing the Staggered Conformation of Ethane

The Case for Steric Repulsion Causing the Staggered Conformation of Ethane

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