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Related Concept Videos

Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride01:26

Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride

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Radical substitution reactions can be used to remove functional groups from molecules. The hydrogenolysis of alkyl halides is one such reaction, where the weak Sn–H bond in tributyltin hydride reacts with alkyl halides to form alkanes. Here, the reagent Bu3SnH yields tributyltin halide as a byproduct.
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...
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Radical Substitution: Allylic Bromination01:27

Radical Substitution: Allylic Bromination

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In organic synthesis, the formation of products can be altered by changing the reaction conditions. For example, a dibromo addition product is formed when propene is treated with bromine at room temperature. In contrast, propene undergoes allylic substitution in non-polar solvents at high temperatures to give 3-bromopropene. In order to avoid the addition reaction, the bromine concentration must be kept as low as possible throughout the reaction. This can be achieved using N-bromosuccinimide...
6.7K
E1 Reaction: Kinetics and Mechanism02:46

E1 Reaction: Kinetics and Mechanism

18.0K
Here, in contrast to the E2 reaction mechanism, we delve into the aspects of the E1 reaction mechanism, which has two steps: rate-limiting loss of the leaving group and abstraction of the beta hydrogen by a weak base. Typically, the experimental proof for the E1 mechanism is via kinetic studies or isotope studies. While the former demonstrates the first-order kinetics—the dependence of the reaction solely on substrate concentration—the latter proves the abstraction of hydrogen only...
18.0K
SN1 Reaction: Mechanism02:25

SN1 Reaction: Mechanism

14.6K
Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism. 
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a...
14.6K
SN2 Reaction: Kinetics02:14

SN2 Reaction: Kinetics

10.4K
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...
10.4K
Alkyl Halides02:45

Alkyl Halides

20.5K
Structural Properties
Alkyl halides are halogen-substituted alkanes wherein one or more hydrogen atoms of an alkane is replaced by a halogen atom such as fluorine, chlorine, bromine, or iodine. The carbon atom in an alkyl halide is bonded to the halogen atom, which is sp3-hybridized and exhibits a tetrahedral shape.
Unlike alkyl halides, compounds in which a halogen atom is bonded to an sp2 -hybridized carbon atom of a carbon-carbon double bond (C=C) are called vinyl halides. Whereas aryl...
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Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films
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Low Pressure Vapor-assisted Solution Process for Tunable Band Gap Pinhole-free Methylammonium Lead Halide Perovskite Films

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First-principles study on the initial decomposition process of CH3NH3PbI3.

Yuanbin Xue1, Yueyue Shan1, Hu Xu1

  • 1Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China.

The Journal of Chemical Physics
|October 2, 2017
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Summary

Hybrid perovskites like methylammonium lead iodide (MAPbI3) are prone to decomposition. First-principles calculations reveal that lead iodide (PbI2) nucleation is the primary decomposition pathway, even without humidity, which acts as a catalyst.

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Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity
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Area of Science:

  • Materials Science
  • Solid State Chemistry
  • Computational Materials Science

Background:

  • Hybrid perovskites are leading candidates for next-generation solar cells due to their high efficiency.
  • The primary limitation for their widespread application is their inherent instability, particularly under humid environments.
  • The precise decomposition mechanisms of hybrid perovskites, such as methylammonium lead iodide (MAPbI3), remain incompletely understood.

Purpose of the Study:

  • To elucidate the initial decomposition mechanisms and structural properties of methylammonium lead iodide (MAPbI3).
  • To investigate the role of humidity in the decomposition process using theoretical calculations.
  • To provide fundamental insights into the intrinsic instability of hybrid perovskites.

Main Methods:

  • Systematic investigation using first-principles calculations.
  • Analysis of energetic favorability for different decomposition pathways.
  • Examination of structural properties during the initial decomposition stages.

Main Results:

  • Energetically, the nucleation and crystallization of lead iodide (PbI2) are favored over other decomposition products from the MAPbI3 matrix.
  • Structural instability is an intrinsic characteristic of MAPbI3, independent of external humidity.
  • Water (H2O) acts as a catalyst, facilitating the desorption of gaseous components by aiding in H+ ion transfer.

Conclusions:

  • The intrinsic structural instability and preferential PbI2 nucleation are key factors contributing to MAPbI3 decomposition.
  • Humidity accelerates decomposition by catalyzing the release of gaseous species.
  • Understanding these mechanisms is crucial for developing more stable hybrid perovskite materials for photovoltaics.