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Amino acids

Amino acids

Amino acids are the monomers that comprise proteins. Each amino acid has the same fundamental structure, which consists of a central carbon atom, or the alpha (α) carbon, bonded to an amino group (NH2), a carboxyl group (COOH), and to a hydrogen atom. Every amino acid also has another atom or group of atoms bonded to the central atom known as the R group. There are 20 common amino acids present in proteins, each with a different R group. Variation in the amino acid sequence is responsible for...

α-Alkylation of Ketones via Enolate Ions

α-Alkylation of Ketones via Enolate Ions

Ketones with α protons are deprotonated by strong bases like lithium diisopropylamide (LDA) to form enolate ions. The anion is stabilized by resonance, and its hybrid structure exhibits negative charges on the carbonyl oxygen and the α carbon. This ambident nucleophile can attack an electrophile via two possible sites: the carbonyl oxygen, known as O-attack, or the α carbon, known as C-attack. The nucleophilic attack via the carbanionic site is preferred. This is due to the strong interaction...

Acid Halides to Amides: Aminolysis

Acid Halides to Amides: Aminolysis

Aminolysis is a nucleophilic acyl substitution reaction, where ammonia or amines act as nucleophiles to give the substitution product. Acid halides react with ammonia, primary amines, and secondary amines to yield primary, secondary, and tertiary amides, respectively.
In the first step of the aminolysis mechanism, the amine attacks the carbonyl carbon of the acyl chloride to form a tetrahedral intermediate. In the second step, the carbonyl group is re-formed with the elimination of a chloride...

Diazonium Group Substitution: –OH and –H

Diazonium Group Substitution: –OH and –H

Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.

Factors Affecting α-Alkylation of Ketones: Choice of Base

Factors Affecting α-Alkylation of Ketones: Choice of Base

α-Alkylation of ketones is achieved in the presence of alkyl halides and a base. The reaction proceeds via the formation of an enolate ion followed by nucleophilic substitution. The choice of base employed is essential as it is the key factor in determining the reaction outcome.
The reaction involving bases like EtO− whose conjugate acid EtOH (pKa = 15.9) is stronger than the ketone (pKa = 19.2) results in an equilibrium mixture with higher ketone concentration. As a consequence, side reactions...

Loss of Carboxy Group as CO2: Decarboxylation of Malonic Acid Derivatives

Loss of Carboxy Group as CO₂: Decarboxylation of Malonic Acid Derivatives

Just like β-keto acids—which upon thermal decarboxylation form ketones—β-dicarboxylic acids undergo decarboxylation to generate monocarboxylic acids with the liberation of carbon dioxide.

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Updated: May 11, 2026

Split-and-pool Synthesis and Characterization of Peptide Tertiary Amide Library

Split-and-pool Synthesis and Characterization of Peptide Tertiary Amide Library

Published on: June 20, 2014

D- or L-alanine: that is the question.

J K Laerdahl¹, R Wesendrup, P Schwerdtfeger

¹Department of Chemistry University of Auckland Private Bag 92019, Auckland, New Zealand.

Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry

|May 23, 2013

Summary

The stability of L-alanine versus D-alanine depends on their specific 3D shapes (conformations). This study found no definitive evidence that naturally occurring L-alanine is always more stable, questioning its origin in life.

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Last Updated: May 11, 2026

Split-and-pool Synthesis and Characterization of Peptide Tertiary Amide Library

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Published on: June 20, 2014

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Published on: June 24, 2016

Area of Science:

Biochemistry
Quantum Chemistry
Astrobiology

Background:

Chirality is fundamental to life, with biological systems predominantly using L-amino acids.
The origin of this homochirality remains a significant scientific question.
Alanine, a simple amino acid, serves as a model system to study enantiomeric stability.

Purpose of the Study:

To investigate the relative stability of L-alanine and D-alanine enantiomers.
To determine if conformational preferences can explain the natural abundance of L-alanine.
To assess the role of parity-violating energy differences in enantiomeric stabilization.

Main Methods:

Computational chemistry methods were employed to calculate energy shifts.
Parity-violating energy differences were computed for 13 stable conformers of gaseous alanine.
Conformational analysis was performed to identify global minima.

Main Results:

Enantiomeric stabilization is highly dependent on the specific conformation of alanine.
L-alanine was found to be the preferred enantiomer in only seven of the thirteen investigated conformers.
No consistent energetic preference for L-alanine over D-alanine was observed across all stable forms.

Conclusions:

The study does not provide a definitive explanation for the origin of homochirality in living organisms based on alanine's intrinsic stability.
Conformational flexibility plays a critical role in determining the relative stability of amino acid enantiomers.
Further research is needed to fully understand the factors driving homochirality in biological systems.