Related Experiment Video
Updated: Jul 18, 2026
16:24
Controlling the Size, Shape and Stability of Supramolecular Polymers in Water
Published on: August 2, 2012
Quantum mechanical size and steric hindrance.
Joshua W Hollett1, Aaron Kelly, Raymond A Poirier
1Department of Chemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X7, Canada. jhollett@mun.ca
The Journal of Physical Chemistry. A
|December 22, 2006
Summary
This study defines molecular size and shape using quantum mechanics. The new method accurately predicts molecular dimensions and steric effects, correlating well with established radii and computational volumes.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Molecular Modeling
Background:
- Accurate definitions of molecular size and shape are crucial for understanding chemical properties and interactions.
- Existing methods for defining molecular dimensions have limitations in certain predictive contexts.
Purpose of the Study:
- To formulate a quantum mechanical definition of molecular size and shape.
- To establish a method invariant to the choice of origin.
- To validate the new definition against experimental and computational data.
Main Methods:
- Utilizing the electronic second moment of the Hartree-Fock wave function.
- Defining a shape tensor invariant with respect to the origin.
- Calculating the geometric average of the tensor's eigenvalues.
Main Results:
- The geometric average of eigenvalues shows strong correlation with van der Waals and Bragg-Slater radii.
- A linear relationship was found between the quantum mechanical size definition and computationally derived molecular volumes.
- The method effectively predicts substituent steric effects, comparable to existing models.
Conclusions:
- A robust quantum mechanical definition of molecular size and shape has been developed.
- This definition provides a reliable and accurate measure of molecular dimensions.
- The approach offers a valuable tool for predicting steric properties in molecular systems.
Related Concept Videos
01:18Directing and Steric Effects in Disubstituted Benzene Derivatives
When disubstituted benzenes undergo electrophilic substitution, the product distribution depends on the directing effect of both substituents. When the directing effects of both substituents reinforce each other, a single product is obtained. For example, bromination of p-nitrotoluene occurs ortho to the methyl group and meta to the nitro group, which is the same position, resulting in a single product. However, if the directing effects of the two groups oppose each other, the more strongly...
01:10Radical Reactivity: Steric Effects
The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic factors, steric factors also account...
Along with electronic factors, steric factors also account...
02:30Stability of Substituted Cyclohexanes
This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
02:11Conformations of Cyclohexane
Cyclohexane does not exist in a planar form due to the high angle and torsional strain it would experience in the planar structure. Instead, it adopts non-planar chair and boat conformations.
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
The chair form is the most stable and derives its name from its resemblance to the “easy chair.” In the chair conformation, two carbon atoms are arranged out-of-plane — one above and one below, minimizing the torsional strain. In the chair form, the bond angle is very close to the ideal tetrahedral value,...
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.