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Related Concept Videos

Stereoisomerism02:52

Stereoisomerism

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Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
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meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H01:13

meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H

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All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...
5.3K
ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH3

5.7K
All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
5.7K
Structural Isomerism02:34

Structural Isomerism

19.1K
Isomerism in Complexes
Isomers are different chemical species that have the same chemical formula. Structural isomerism of coordination compounds can be divided into two subcategories, the linkage isomers and coordination-sphere isomers.
Linkage isomers occur when the coordination compound contains a ligand that can bind to the transition metal center through two different atoms. For example, the CN− ligand can bind through the carbon atom or through the nitrogen atom. Similarly, SCN− can...
19.1K
Nucleophilic Substitution Reactions02:34

Nucleophilic Substitution Reactions

15.9K
Historical perspective
In 1896, the German chemist Paul Walden discovered that he could interconvert pure enantiomeric (+) and (-) malic acids through a series of reactions. This conversion suggested the involvement of optical inversion during the substitution reaction. Further, in 1930, Sir Christopher Ingold described for the first time two different forms of nucleophilic substitution reactions, which are known as SN1 (nucleophilic substitution unimolecular) and SN2 (nucleophilic substitution...
15.9K
Diazonium Group Substitution: –OH and –H01:19

Diazonium Group Substitution: –OH and –H

2.7K
Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.
2.7K

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Related Experiment Video

Updated: May 24, 2025

High-Contrast and Fast Photorheological Switching of a Twist-Bend Nematic Liquid Crystal
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pH-Dependent Switching Between Nonlinear-Optical-Active Nitrate-Based Supramolecular Polymorphs.

Qiao Xia1, Xingxing Jiang2, Chunbo Jiang1

  • 1China-Australia Joint Research Center for Functional Molecular Materials, School of Chemical Science and Engineering, Tongji University, Shanghai, 200092, China.

Angewandte Chemie (International Ed. in English)
|March 1, 2025
PubMed
Summary
This summary is machine-generated.

Researchers developed a novel pH-modulation strategy to synthesize three non-centrosymmetric (NCS) nitrate supramolecular polymorphs. This method controls secondary bonds, enabling tailored nonlinear optical (NLO) properties in these advanced materials.

Keywords:
NitratesNonlinear opticsPhase transitionsPolymorphsStructure‐property relationships

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Patterning via Optical Saturable Transitions - Fabrication and Characterization
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Patterning via Optical Saturable Transitions - Fabrication and Characterization

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Area of Science:

  • Materials Science
  • Crystallography
  • Nonlinear Optics

Background:

  • Synthesizing non-centrosymmetric (NCS) second-order nonlinear optical (NLO) crystals, especially metastable polymorphs, is difficult due to complex interactions.
  • Controlling crystal structures is key to achieving desired NLO properties.

Purpose of the Study:

  • To report the first synthesis of three nitrate supramolecular polymorphs (α-, β-, and γ-phases) using a pH-modulation secondary-bond strategy.
  • To investigate the influence of pH on secondary bond orientation and its effect on crystal packing and NLO properties.

Main Methods:

  • Utilized a pH-modulation strategy to assemble π-conjugated planar primitives ([C2H5N4] and [NO3]).
  • Varied solution pH to control secondary bond orientation and influence crystal lattice packing.
  • Investigated polymorph transformations (e.g., 2D α-phase to 2D β-phase) and their impact on NLO responses.

Main Results:

  • Successfully synthesized three nitrate supramolecular polymorphs (α-, β-, and γ-phases) with varying NCS characteristics.
  • Demonstrated that pH-induced secondary bond variations dictate crystal packing and can lead to different NLO properties.
  • Observed distinct second harmonic generation (SHG) responses and birefringences in the α- and β-phases, linked to hydrogen-bond layer stacking.

Conclusions:

  • Secondary-bond interactions are crucial for forming rare nitrate supramolecular polymorphs and controlling their structures.
  • The pH-modulation strategy provides a new paradigm for developing high-performance NCS materials with tailored optical properties.
  • Elucidated supramolecular polymorph transition mechanisms and structure-property correlations for NLO materials.