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Related Concept Videos

Structure of Conjugated Dienes01:16

Structure of Conjugated Dienes

Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
Stability of Conjugated Dienes01:28

Stability of Conjugated Dienes

Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
Disubstituted Cyclohexanes: cis-trans Isomerism02:37

Disubstituted Cyclohexanes: cis-trans Isomerism

Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers.
Characteristics and Nomenclature of Homopolymers01:00

Characteristics and Nomenclature of Homopolymers

Polymers that are made up of identical monomer units are called homopolymers. Only one repeating unit is involved in the construction of the homopolymer structure. For example, as depicted in Figure 1, polypropylene is a homopolymer constituted of propylene monomers. Here, the only repeating unit in the polymer chain is propylene.
Isomerism02:43

Isomerism

Isomers are molecules with the same molecular formula but different structural arrangements. Isomers can be further classified into constitutional isomers and stereoisomers. Constitutional isomers differ in the connectivity of their constituent atoms. For example, 2-butanol and diethyl ether are constitutional isomers, as they have the same chemical formula, C4H10O, but differ in the connectivity of the carbon and oxygen atoms. Constitutional isomers have different physical and chemical...
Stereoisomerism of Cyclic Compounds02:33

Stereoisomerism of Cyclic Compounds

In this lesson, we delve into the role of ring conformation and its stability, which determines the spatial arrangement and, consequently, the molecular symmetry and stereoisomerism of cyclic compounds. 1,2-Dimethylcyclohexane is used as a case study to evaluate the possible number of stereoisomers. Here, given the multiple (n = 2) chiral centers, there are 2n = 4 possible configurations that lack a plane of symmetry, as the ring skeleton exists in a non-planar chair conformation. In addition,...

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Self-assembling Morphologies Obtained from Helical Polycarbodiimide Copolymers and Their Triazole Derivatives
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Form, function and functionality of two dimeric toluene-2,4-diisocyanate polymorphs.

Liana Vella-Zarb1, Robert E Dinnebier

  • 1Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.

Acta Crystallographica. Section B, Structural Science
|March 23, 2012
PubMed
Summary

Toluene diisocyanate (TDI) exists in two polymorphic forms, A and B, with similar crystal structures but different physical properties. Energy analysis revealed the driving forces behind these property variations.

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Area of Science:

  • Polymer Science
  • Materials Science
  • Crystallography

Background:

  • Toluene diisocyanate (TDI) is a crucial aromatic diisocyanate in polymer manufacturing.
  • TDI exhibits polymorphism, crystallizing into distinct forms (A and B) influenced by reaction conditions.
  • Polymorphic forms can possess significantly different physical properties, impacting material performance.

Purpose of the Study:

  • To determine the crystal structures of TDI's polymorphic forms A and B.
  • To investigate the reasons behind the differing physical properties of TDI polymorphs.
  • To analyze the energy contributions governing the behavior of TDI polymorphs.

Main Methods:

  • High-resolution laboratory X-ray powder diffraction was employed for structural determination.
  • Simulated annealing and Rietveld refinement techniques were utilized for crystal structure analysis.
  • Partitioned energy terms were calculated and analyzed to understand property differences.

Main Results:

  • The crystal structures of TDI's polymorphic forms A and B were successfully determined.
  • Despite structural similarities, significant discrepancies in physical properties between form A and form B were observed.
  • Energy analysis provided insights into the molecular interactions responsible for the observed property variations.

Conclusions:

  • The study elucidates the structural and energetic basis for the differing physical properties of TDI polymorphs.
  • Understanding these differences is critical for controlling TDI crystallization and optimizing polymer properties.
  • This research contributes to the fundamental knowledge of aromatic diisocyanate polymorphism and its implications in materials science.