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01:18Aromatic Hydrocarbon Cations: Structural Overview
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Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group...
Removing one hydrogen from the intervening CH2 group...
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01:00Characteristics and Nomenclature of Homopolymers
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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.
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01:17Ziegler–Natta Chain-Growth Polymerization: Overview
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Ziegler–Natta polymerization is another form of addition or chain‐growth polymerization used for synthesizing linear polymers over branched polymers. The catalyst used for polymerization is the Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, who developed it in 1953. This catalyst is an organometallic complex of titanium tetrachloride and triethyl aluminum, with the active form of the catalyst being an alkyl titanium compound. Using the Ziegler–Natta...
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02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
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Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
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01:26Thermal and Photochemical Electrocyclic Reactions: Overview
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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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01:17Thermal Electrocyclic Reactions: Stereochemistry
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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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Tetrazene-Characterization of Its Polymorphs.
Jan Ryšavý1, Robert Matyáš1, Zdeněk Jalový1
1Institute of Energetic Materials, Faculty of Chemical Technology, University of Pardubice, 53210 Pardubice, Czech Republic.
Molecules (Basel, Switzerland)
|December 10, 2021
Summary
Researchers reinvestigated tetrazene crystal structure, identifying a new C form as the primary product. Transition to the A form requires time, temperature, and water, with both forms showing similar industrial applications.
Keywords:
Raman spectroscopyX-ray diffractioninfrared spectroscopypolymorphismprimerssensitivitytetrazeneMore Related Videos
Area of Science:
- Crystallography and Materials Science
- Solid-state chemistry of energetic materials
Background:
- Previous structural data for tetrazene may not fully represent all crystalline forms.
- Understanding different crystalline modifications is crucial for controlling material properties.
Purpose of the Study:
- To reinvestigate the crystal structure of tetrazene.
- To identify and characterize different crystalline forms and their formation conditions.
- To assign vibrational modes and compare the properties of different tetrazene modifications.
Main Methods:
- X-ray diffraction (single crystal and powder) for structural determination.
- Infrared and Raman spectroscopy for vibrational analysis.
- Isotopic labeling (15N) for mode assignment.
- Mechanical stimuli testing and primer performance evaluation.
Main Results:
- A new crystalline form (C form) of tetrazene was identified as the primary reaction product.
- The transition from the C form to the previously known A form is dependent on temperature, water presence, and time.
- Both X-ray powder diffraction and vibrational spectroscopy (IR and Raman) successfully differentiated between the two forms.
- 15N isotopic labeling aided in assigning specific vibrational modes.
- No significant differences in sensitivity to mechanical stimuli or performance in primer compositions were found between the A and C forms.
Conclusions:
- The study clarifies the structural polymorphism of tetrazene and the conditions governing the formation of different crystalline forms.
- Despite structural differences, the investigated properties (mechanical sensitivity, primer performance) of the A and C forms are comparable, suggesting robustness in applications.
- Vibrational spectroscopy, enhanced by isotopic labeling, provides a reliable method for distinguishing between tetrazene polymorphs.