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Related Concept Videos

meta-Directing Deactivators: –NO2, –CN, –CHO, –⁠CO2R, –COR, –CO2H01:13

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

6.6K
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...
6.6K
2° Amines to N-Nitrosamines: Reaction with NaNO201:20

2° Amines to N-Nitrosamines: Reaction with NaNO2

5.4K
Secondary amines react with nitrous acid to form N-nitrosamines, as depicted in Figure 1. Nitrous acid, a weak and unstable acid, is formed in situ from an aqueous solution of sodium nitrite and strong acids, such as hydrochloric acid or sulfuric acid, in cold conditions. In the presence of an acid, the nitrous acid gets protonated. The subsequent loss of water results in the formation of the electrophile known as nitrosonium ion.
5.4K
SN2 Reaction: Kinetics02:14

SN2 Reaction: Kinetics

10.2K
Kinetic Studies and Significance
In a chemical reaction, a relationship exists between the concentration of reactants and the rate at which the reaction proceeds. The study to measure this relationship is known as the kinetics of a chemical reaction. Kinetic studies are used to deduce the rate law of a chemical reaction, which provides information about the species involved during the transition state of the rate-determining step. Thus, kinetic studies help to derive the mechanism of a...
10.2K
SN2 Reaction: Mechanism02:27

SN2 Reaction: Mechanism

17.2K
The kinetic studies of SN2 reactions suggest an essential feature of its mechanism: it is a single-step process without intermediates. Here, both the nucleophile and the substrate participate in the rate-determining step.
The presence of the more electronegative halogen in the substrate creates a polarized carbon-halide bond. The halide pulls the electron cloud generating an electrophilic center at the carbon atom. Thus, the carbon atom carries a partial positive charge while the halide has a...
17.2K
SN2 Reaction: Transition State02:26

SN2 Reaction: Transition State

11.7K
An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
11.7K
SN2 Reaction: Stereochemistry02:23

SN2 Reaction: Stereochemistry

11.6K
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not...
11.6K

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Fabrication of VB2/Air Cells for Electrochemical Testing
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2 × 2 optofluidic switch chip with an air shutter.

Peng Xu, Jing Wan, Simo Zhang

    Applied Optics
    |June 29, 2019
    PubMed
    Summary

    A novel 2x2 optofluidic switch chip with an air shutter offers excellent performance across a broad waveband. Optimization of microchannel width and structure significantly enhances its optical switching capabilities.

    Area of Science:

    • Photonics
    • Microfluidics
    • Optical Engineering

    Background:

    • Optofluidic devices integrate optical functionalities with microfluidic systems.
    • Efficient and compact optical switches are crucial for advanced photonic integrated circuits.
    • Previous optofluidic switches faced challenges in performance metrics like crosstalk and extinction ratio.

    Purpose of the Study:

    • To propose and characterize a novel 2x2 optofluidic switch chip utilizing an air shutter.
    • To investigate the impact of microchannel width and structural optimization on switch performance.
    • To achieve high extinction ratios, low crosstalk, and low insertion loss over a broad operational waveband.

    Main Methods:

    • Design and fabrication of a 2x2 optofluidic switch chip featuring an air shutter.

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  • Systematic analysis of microchannel width effects on optical switch performance.
  • Structural optimization, including the transition from a symmetrical to a semi-tapered design.
  • Performance evaluation at a 1310 nm wavelength, measuring insertion loss, extinction ratio, and crosstalk.

    • Main Results:

    • The proposed optofluidic switch exhibits a simple structure, small volume, and broad operation waveband (400-1700 nm).
    • Optimal microchannel width for comprehensive 'on' state performance was determined to be 4.0 μm.
    • Structural optimization to a semi-tapered design further improved switch characteristics.
    • Achieved performance at 1310 nm: 0.41 dB insertion loss ('on'), 0.15 dB ('off'); 52.5 dB extinction ratio ('on'), 28.3 dB ('off'); -28.8 dB crosstalk ('on'), -52.6 dB ('off').

    Conclusions:

    • The developed 2x2 optofluidic switch chip demonstrates superior performance, including high extinction ratios and low crosstalk.
    • The design shows good scalability for constructing larger optical switching matrices.
    • Microfluidic control combined with optimized optical structures offers a promising avenue for advanced photonic devices.