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Alkyl Halides02:45

Alkyl Halides

17.6K
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...
17.6K
Ionic Crystal Structures02:42

Ionic Crystal Structures

15.4K
Ionic crystals consist of two or more different kinds of ions that usually have different sizes. The packing of these ions into a crystal structure is more complex than the packing of metal atoms that are the same size.
Most monatomic ions behave as charged spheres, and their attraction for ions of opposite charge is the same in every direction. Consequently, stable structures for ionic compounds result (1) when ions of one charge are surrounded by as many ions as possible of the opposite...
15.4K
Electrophilic Addition to Alkynes: Halogenation02:38

Electrophilic Addition to Alkynes: Halogenation

8.8K
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
8.8K
Acid Halides to Carboxylic Acids: Hydrolysis01:01

Acid Halides to Carboxylic Acids: Hydrolysis

2.9K
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic...
2.9K
Aromatic Hydrocarbon Cations: Structural Overview01:18

Aromatic Hydrocarbon Cations: Structural Overview

3.1K
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...
3.1K
ortho–para-Directing Deactivators: Halogens01:24

ortho–para-Directing Deactivators: Halogens

6.0K
Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
6.0K

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Rethinking the A cation in halide perovskites.

Jin-Wook Lee1, Shaun Tan2,3, Sang Il Seok4

  • 1SKKU Advanced Institute of Nanotechnology (SAINT) and Department of Nanoengineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.

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The A cation in organic-inorganic lead halide perovskites (OLHPs) significantly impacts optoelectronic properties, contrary to prior beliefs. This review explores breakthroughs and future directions driven by A-cation versatility in OLHPs.

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Area of Science:

  • Materials Science
  • Solid-State Chemistry
  • Photovoltaics

Background:

  • Organic-inorganic lead halide perovskites (OLHPs) are promising photovoltaic materials.
  • The A-site cation's influence on OLHP properties was historically underestimated.
  • Recent research highlights the A-site cation's crucial role in tuning OLHP characteristics.

Purpose of the Study:

  • To review recent advancements in understanding the A-cation's role in OLHPs.
  • To highlight breakthroughs enabled by A-cation tunability.
  • To identify future research opportunities and open questions concerning the A-cation in OLHPs.

Main Methods:

  • Literature review of recent studies on OLHPs.
  • Analysis of structure-property relationships in A-cation-modified OLHPs.
  • Synthesis of findings on physicochemical and optoelectronic property modulation.

Main Results:

  • The A-cation critically influences the physicochemical and optoelectronic properties of OLHPs.
  • Versatility of the A-cation allows for targeted property engineering.
  • Significant progress has been made in leveraging A-cation modifications for enhanced performance.

Conclusions:

  • The A-cation is a key determinant of OLHP performance.
  • Further exploration of A-cation chemistry offers vast potential for next-generation OLHP devices.
  • Understanding A-cation interactions is crucial for overcoming current limitations and advancing the field.