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Related Concept Videos

Chair Conformation of Cyclohexane02:02

Chair Conformation of Cyclohexane

14.2K
The chair conformation is the most stable form of cyclohexane due to the absence of angle and torsional strain. The absence of angle strain is a result of cyclohexane’s bond angle being very close to the ideal tetrahedral bond angle of 109.5° in its chair conformer. Similarly, the torsional strain is also absent owing to the perfectly staggered arrangement of bonds.
The hydrogen atoms linked to carbons are arranged in two different axial and equatorial orientations to achieve this...
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Stability of Substituted Cyclohexanes02:30

Stability of Substituted Cyclohexanes

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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...
12.2K
Conformations of Cyclohexane02:11

Conformations of Cyclohexane

12.0K
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...
12.0K
Newman Projections02:06

Newman Projections

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Different notations are used to represent the three-dimensional structure of molecules on two-dimensional surfaces. One of the most commonly used representations is the dash-wedge formula. The dashed wedges, solid wedges, and the plane lines indicate the groups situated behind the plane, coming out of the plane, and in the plane, respectively.
The organic molecules rotate across the single bonds leading to numerous temporary three-dimensional structures of varying energy known as...
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¹H NMR of Conformationally Flexible Molecules: Temporal Resolution00:52

¹H NMR of Conformationally Flexible Molecules: Temporal Resolution

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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...
789
Conformations of Cycloalkanes02:29

Conformations of Cycloalkanes

11.4K
Adolf von Baeyer attempted to explain the instabilities of small and large cycloalkane rings using the concept of angle strain — the strain caused by the deviation of bond angles from the ideal 109.5° tetrahedral value for sp3  hybridized carbons. However, while cyclopropane and cyclobutane are strained, as expected from their highly compressed bond angles, cyclopentane is more strained than predicted, and cyclohexane is virtually strain-free. Hence, Baeyer’s theory that...
11.4K

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Choreoisosteres: Pseudoatom Variation in Macrocyclic Hinges Conserves Structure and Dynamics.

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Three macrocycles with isosteric substitutions exhibit identical hinge-like motion barriers. This conserved dynamic behavior allows for predictable physical properties like hydrophobicity and diffusion.

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Area of Science:

  • Organic Chemistry
  • Chemical Dynamics
  • Molecular Modeling

Background:

  • Macrocyclic compounds are crucial in various chemical and biological applications.
  • Understanding the dynamic behavior of macrocycles is key to predicting their properties.
  • Isosteric substitutions offer a way to fine-tune molecular characteristics.

Purpose of the Study:

  • To investigate the dynamic behavior of three choreoisosteric macrocycles.
  • To quantify the energy barriers associated with their hinge-like motion.
  • To explore the predictability of physical properties based on conserved dynamics.

Main Methods:

  • Synthesis of three macrocycles with geminal dimethyl, cyclopropyl, and cyclobutyl substitutions.
  • Variable-temperature 13C Nuclear Magnetic Resonance (NMR) spectroscopy to determine energy barriers.
  • Analysis of physical properties including hydrophobicity and diffusion constants.

Main Results:

  • All three macrocycles demonstrated a conserved, fully revolute hinge-like motion in solution.
  • The energy barriers to hinging (ΔG‡) were found to be identical within experimental error (14.2-15.2 kcal/mol).
  • Physical properties such as hydrophobicity and diffusion constants showed consistency with the conserved dynamic behavior.

Conclusions:

  • Choreoisosteric substitutions in macrocycles can lead to conserved dynamic properties.
  • The hinge-like motion and its associated energy barriers are robust across these specific isosteric changes.
  • This conserved dynamic behavior facilitates the prediction of other physical properties, aiding in molecular design.