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Related Concept Videos

Angle of Twist - Elastic Range01:13

Angle of Twist - Elastic Range

Consider a cylindrical shaft with a length denoted by L and a consistent cross-sectional radius referred to as r. This shaft undergoes a torque at the free end. The highest shearing strain within the shaft is directly proportional to the twist angle and the radial distance from the shaft axis. When the shaft behaves elastically, this shearing strain can be articulated using variables such as the applied torque, radial distance, the polar moment of inertia, and the modulus of rigidity. By...
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Unsymmetric Bending

Unsymmetrical bending occurs when the bending moment applied to a structural member does not align with its principal axis. This misalignment leads to complex stress distributions and deflection patterns that differ from those in symmetrical bending, and are essential for designing structures to withstand different loading conditions. In unsymmetrical bending, the neutral axis—where stress is zero—does not necessarily align with the geometric axes of the cross-section. The orientation of the...
Aromatic Hydrocarbon Anions: Structural Overview01:18

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Neutral hydrocarbons like cyclopentadiene with an odd number of carbon atoms and one intervening CH2 group in the ring are not aromatic. Cyclopentadiene with 4 π electrons does not satisfy the 4n + 2 π electron rule. Additionally, the intervening CH2 group is sp3 hybridized and lacks a vacant p orbital, thereby interrupting the overlap of p orbitals in a continuous manner and preventing the delocalization of π electrons throughout the ring.
Due to the absence of continuous overlap of p...
Angle of Twist: Problem Solving01:13

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An electric motor applies a torque of 700 N·m to an aluminum shaft, triggering a stable rotation. Two pulleys, B and C, are subjected to torques of 300 N·m and 400 N·m, respectively. The modulus of rigidity is provided as 25 GPa. With the knowledge of the length and diameter of each segment, the twist angle between the two pulleys can be computed. First, a section cut is made between pulleys B and C, and the cut cross-section is analyzed using a free-body diagram. Given that the torque exerted...
Torsion of Noncircular Members01:16

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Circular shafts undergoing torsional stress maintain their cross-sectional integrity due to their axisymmetric nature. This symmetry ensures an even distribution of stress, allowing the shaft to withstand torsion without distorting. In contrast, square bars, lacking this axial symmetry, experience significant distortion across their cross-sections when subjected to torsion, with the exception of along their diagonals and at lines connecting midpoints. A detailed examination of a cubic element...
Conformations of Cycloalkanes02:29

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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 was based on the...

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Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units
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Twisted arenes.

Kung K Wang1

  • 1C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, WV, 26506-6045, USA, kung.wang@mail.wvu.edu.

Topics in Current Chemistry
|September 8, 2012
PubMed
Summary
This summary is machine-generated.

Steric interactions in polycyclic aromatic hydrocarbons cause significant twisting, distorting their planar structures. X-ray crystallography confirms these twists and their impact on molecular stability.

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Area of Science:

  • Organic Chemistry
  • Crystallography
  • Molecular Structure

Background:

  • Polycyclic aromatic hydrocarbons (PAHs) are typically planar.
  • Substituent groups can introduce steric hindrance.
  • Steric hindrance can force deviations from planarity.

Purpose of the Study:

  • To investigate the structural distortions in substituted PAHs.
  • To understand the relationship between steric interactions and molecular twisting.
  • To determine the configurational stability of twisted aromatic systems.

Main Methods:

  • X-ray crystallography was used to determine the three-dimensional structures.
  • Direct measurements of structural distortions were performed.
  • Configurational stability was assessed for twisted arenes.

Main Results:

  • Substituents at specific positions (e.g., C4/C5 in phenanthrene) induce non-planar twists.
  • Helical twists were observed in benzo[c]phenanthrene and dibenzo[g]phenanthrene derivatives.
  • Highly substituted acenes like octamethylnaphthalene show end-to-end twists.

Conclusions:

  • Steric interactions are the primary drivers of non-planarity and twisting in these aromatic systems.
  • X-ray structures provide quantitative data on these molecular distortions.
  • The study provides insights into the stability of non-planar aromatic frameworks.