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Related Concept Videos

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule02:17

Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule

If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
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Replacing each alpha-hydrogen in chloroethane by bromine (or a different functional group) yields a pair of enantiomers. Such protons are called prochiral or enantiotopic and are related by a mirror plane. Enantiotopic protons are chemically equivalent in an achiral environment. Because most proton NMR spectra are recorded using achiral solvents, enantiotopic hydrogens yield a single signal.
In chiral compounds such as 2-butanol, replacing the methylene hydrogens at C3 produces a pair of...
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Prochirality

The concept of prochirality leads to the nomenclature of the individual faces of a molecule and plays a crucial role in the enantioselective reaction. It is a concept where two or more achiral molecules react to produce chiral products. A typical process is the reaction of an achiral ketone to generate a chiral alcohol. Here, the achiral reactant reacts with an achiral reducing agent, sodium borohydride, to generate an equimolar mixture of the chiral enantiomers of the product. For example, an...
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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

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At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
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Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).

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How the generalized anomeric effect influences the conformational preference.

Changwei Wang1, Zhenhua Chen, Wei Wu

  • 1The State Key Laboratory of Physical Chemistry of Solid Surfaces, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, Fujian 361005, PR China.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|December 11, 2012
PubMed
Summary
This summary is machine-generated.

The generalized anomeric effect

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Area of Science:

  • Computational Chemistry
  • Quantum Chemistry
  • Molecular Modeling

Background:

  • The generalized anomeric effect describes a molecular conformational preference.
  • Conflicting theories exist regarding its origin, with steric and hyperconjugative interactions implicated.
  • Understanding this effect is crucial in various chemical contexts.

Purpose of the Study:

  • To quantitatively assess the contribution of hyperconjugation to the generalized anomeric effect.
  • To investigate the role of steric and hyperconjugative interactions in different acyclic systems.
  • To resolve the debate surrounding the origin of the generalized anomeric effect.

Main Methods:

  • Utilized the block-localized wavefunction (BLW) method, a simplified ab initio valence bond (VB) theory approach.
  • Employed self-consistent field calculations to define electron-localized reference states.
  • Performed energy decomposition analysis to differentiate interaction contributions.

Main Results:

  • For methoxymethyl fluoride and chlorides, both steric and hyperconjugative effects influence conformation.
  • In methanediol, methanediamine, aminomethanol, and dimethoxymethane, hyperconjugation negatively impacts conformation.
  • Steric interactions were identified as the sole driver of the generalized anomeric effect in these latter systems.

Conclusions:

  • Hyperconjugation's role in the generalized anomeric effect is system-dependent.
  • Steric effects are the primary determinant of the generalized anomeric effect in several key molecules.
  • The BLW method provides valuable insights into molecular conformational preferences.