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Related Concept Videos

Preparation and Reactions of Thiols02:33

Preparation and Reactions of Thiols

6.2K
Thiols are prepared using the hydrosulfide anion as a nucleophile in a nucleophilic substitution reaction with alkyl halides. For instance, bromobutane reacts with sodium hydrosulfide to give butanethiol.
6.2K
Preparation and Reactions of Sulfides02:26

Preparation and Reactions of Sulfides

4.8K
Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.
4.8K
Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride01:26

Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride

1.8K
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...
1.8K
SN1 Reaction: Mechanism02:25

SN1 Reaction: Mechanism

11.9K
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...
11.9K
Introduction to Electrophilic Addition Reactions of Alkenes02:24

Introduction to Electrophilic Addition Reactions of Alkenes

7.9K
The double bond in a simple, unconjugated alkene is a region of high electron density that can act as a weak base or a nucleophile. The filled π orbital (HOMO) of the double bond can interact with the empty LUMO of an electrophile. A bonding interaction occurs when the electrophile attacks between the two carbons; the electrophile then accepts a pair of electrons from the π bond and undergoes addition across the double bond, yielding a single product.
Addition and elimination...
7.9K
Acid Halides to Carboxylic Acids: Hydrolysis01:01

Acid Halides to Carboxylic Acids: Hydrolysis

2.6K
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...
2.6K

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Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation
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Hydrogen-Bonded Thiol Undergoes Unconventional Excited-State Intramolecular Proton-Transfer Reactions.

Jian-Kai Wang1, Chih-Hsing Wang1, Chi-Chi Wu1

  • 1Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan, Republic of China.

Journal of the American Chemical Society
|January 30, 2024
PubMed
Summary

This study explores thiol hydrogen bonds and excited-state intramolecular proton transfer (ESIPT) in novel mercaptoflavones. Results reveal proton-accepting strength, not thiol acidity, governs the unconventional ESIPT mechanism.

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Analyzing Protein Dynamics Using Hydrogen Exchange Mass Spectrometry
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Area of Science:

  • Photochemistry
  • Supramolecular Chemistry
  • Organic Chemistry

Background:

  • Thiol hydrogen bonds (H-bonds) exhibit unconventional properties compared to traditional O-H or N-H H-bonds.
  • Excited-state intramolecular proton transfer (ESIPT) in thiol systems can be nonemissive due to dominant nπ* character.
  • Understanding the fundamental differences in ESIPT mechanisms is crucial for developing novel photoluminescent materials.

Purpose of the Study:

  • To investigate the influence of H-bond strength on ESIPT in a series of 4'-substituted-7-diethylamino-3-mercaptoflavones (NTFs).
  • To elucidate the driving forces behind the unconventional ESIPT reaction in thiol-based systems.
  • To explore the relationship between molecular structure, H-bond characteristics, and photophysical properties.

Main Methods:

  • Synthesis of a new series of 4'-substituted-7-diethylamino-3-mercaptoflavones (NTFs) with varied H-bond strengths.
  • Spectroscopic analysis (UV-Vis absorption, fluorescence emission) to characterize tautomer emission.
  • Fluorescence upconversion spectroscopy to measure the rate of -SH ESIPT in toluene.

Main Results:

  • Synthesized NTFs exhibit tautomeric emission between 690-720 nm upon UV excitation.
  • Experimental determination of H-bonding strength order: N-NTF < O-NTF < H-NTF < F-NTF.
  • Observed an inverse correlation between H-bond strength and ESIPT rate (F-NTF, strongest H-bond, showed slowest ESIPT), contradicting conventional models.
  • Rationalized results by carbonyl oxygen basicity, indicating proton-accepting strength governs ESIPT, not -SH acidity.

Conclusions:

  • The ESIPT reaction in the studied noncanonical thiol H-bonding systems is unconventional.
  • Proton-accepting ability of the carbonyl oxygen is the primary driver for ESIPT, overriding thiol acidity.
  • Findings provide new insights into the mechanism of ESIPT in thiol-containing molecules, paving the way for designing advanced functional materials.