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Relative Reactivity of Carboxylic Acid Derivatives

Relative Reactivity of Carboxylic Acid Derivatives

Carboxylic acid derivatives such as acid halides, anhydrides, esters, and amides undergo nucleophilic acyl substitution reactions with varying degrees of reactivity.
A key factor in assessing the reactivity of the acid derivatives is the basicity of the substituent or the leaving group. The lower the basicity of the leaving group, the higher the reactivity of the derivative. The basicity of the leaving group follows this order:
Halide ions < Acyloxy ions < Alkoxy ions < Amine ions

Leaving Groups

Leaving Groups

The nature of leaving groups strongly influences the outcome of a nucleophilic substitution reaction.
In general, in a nucleophilic substitution reaction, a nucleophile displaces a functional group, called the leaving group, from the substrate to give a substituted product. A leaving group departs the substrate molecule through heterolytic cleavage, taking the pair of electrons with it to become a relatively stable weak base in the form of an anion or a neutral molecule.
In a...

SN2 Reaction: Stereochemistry

S_N2 Reaction: Stereochemistry

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...

E2 Reaction: Stereochemistry and Regiochemistry

E2 Reaction: Stereochemistry and Regiochemistry

Elimination reactions of alkyl halides can yield one or more alkenes depending on the specific regiochemical and stereochemical considerations. While the regiochemistry of the reaction governs the location of the double bond in the product, the stereochemical requirements often influence the geometry.
When a substrate with two different β hydrogens undergoes an E2 elimination, the presence of a strong base can yield two regioisomeric alkenes. The more-substituted alkene is the major...

E1 Reaction: Kinetics and Mechanism

E1 Reaction: Kinetics and Mechanism

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...

Preparation and Reactions of Sulfides

Preparation and Reactions of Sulfides

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.

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Related Experiment Video

Updated: Feb 20, 2026

Regioselective O-Glycosylation of Nucleosides via the Temporary 2',3'-Diol Protection by a Boronic Ester for the Synthesis of Disaccharide Nucleosides

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Published on: July 26, 2018

Remarkable Reactivity Differences between Glucosides with Identical Leaving Groups.

Tianmeng Duo¹, Kyle Robinson¹, Ian R Greig¹

¹Department of Chemistry, University of British Columbia , 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada.

Journal of the American Chemical Society

|October 17, 2017

Summary

This summary is machine-generated.

Two isomeric fluorinated glucosides show a million-fold difference in enzyme reaction rates, stemming from inherent molecular properties, not enzyme interactions. Non-enzymatic hydrolysis also revealed significant rate variations.

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A Straightforward Method for Glucosinolate Extraction and Analysis with High-pressure Liquid Chromatography HPLC

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Published on: March 15, 2017

Area of Science:

Biochemistry
Enzymology
Organic Chemistry

Background:

β-glucosidases are crucial enzymes in carbohydrate metabolism.
Understanding substrate specificity and reaction mechanisms is key to enzyme function.
Isomeric compounds can exhibit vastly different reactivity profiles.

Purpose of the Study:

To investigate the significant rate differences in the enzymatic hydrolysis of two isomeric aryl 2-deoxy-2-fluoro-β-glucosides.
To elucidate the origins of these rate differences by examining non-enzymatic hydrolysis and molecular properties.
To determine the contribution of ground state and transition state effects to the observed reactivity.

Main Methods:

Enzymatic hydrolysis kinetics using β-glucosidase.
Non-enzymatic (spontaneous) hydrolysis studies.
¹⁸O-labeling experiments to probe reaction mechanisms.
X-ray crystallography and quantum chemical calculations.

Main Results:

A 10⁶-fold difference in reaction rates was observed between the two isomeric substrates with β-glucosidase.
Non-enzymatic hydrolysis showed a 10⁵-fold rate difference, indicating inherent substrate properties are responsible.
¹⁸O-labeling excluded an alternative nucleophilic aryl substitution mechanism.
X-ray and computational studies revealed that ground state destabilization and transition state stabilization contribute equally to reactivity differences.

Conclusions:

The dramatic rate differences in β-glucosidase activity are primarily due to inherent properties of the isomeric substrates.
Both ground state destabilization and transition state stabilization play significant, nearly equal roles in modulating reactivity.
Simple equilibrium measures like pK_a are insufficient to predict leaving group ability in complex enzymatic reactions.