Ester functional group, generic 2D structure R–C(=O)–OR′ with carbonyl and alkoxy, carboxylate ester

Ester (Functional Group) Chemical Structure

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1. Identification

Summary

Ester denotes the carboxylate ester functional group with general formula R–C(=O)–OR′ (R, R′ = carbon substituents). Esters are polar, aprotic, H-bond acceptors (C=O, C–O) but not donors, display a characteristic IR C=O band ~1735 cm⁻¹ for saturated aliphatic esters (lower with conjugation or ring strain), and strong C–O stretches ~1050–1300 cm⁻¹. ¹³C NMR carbonyl resonates ~160–175 ppm; ¹H NMR O-alkyl protons commonly ~3.7–4.3 ppm. IUPAC naming: alkyl alkanoate (e.g., ethyl ethanoate).

Brand Names

Not applicable.

Name

Ester (carboxylate ester)

Background

Ubiquitous in natural products (fats as triacylglycerols, lactones) and pharmaceuticals (prodrugs). Common preparations:
• Fischer esterification (carboxylic acid + alcohol, acid catalysis, water removal)
• Steglich/Yamaguchi variants (DCC/EDC + DMAP; mixed anhydrides)
• Acid chloride/anhydride + alcohol (base capture of HX)
• Transesterification (alcoholate/base or acid catalysis)
• Lactonization (intramolecular, hydroxy acids → cyclic esters)

Modality

Functional group (small-molecule chemistry)

Groups

Endogenous biomolecules; industrial and medicinal chemistry motif

Structure

Generic ester (R–C(=O)–OR′): polar aprotic, H-bond acceptor; hallmark IR C=O ~1735 cm⁻¹ and C–O 1050–1300 cm⁻¹; versatile in hydrolysis, transesterification, reduction, and Claisen chemistry.
Ester functional group, generic 2D structure R–C(=O)–OR′ with carbonyl and alkoxy, carboxylate ester

Weight

Not applicable (class)

Chemical Formula

R–C(=O)–OR′

Synonyms

Carboxylate ester; Alkyl alkanoate; –COOR

External IDs

Not applicable (generic functional group)

2. Pharmacology

Indication

Not a drug (group descriptor).

Associated Conditions

Occurs in lipids, fragrances/flavors, and many APIs; frequently used in prodrug design to mask acidic/alcoholic groups and improve permeability.

Associated Therapies

Ester prodrugs hydrolyzed by carboxylesterases/paraoxonases to release the active acid/alcohol.

Contraindications & Blackbox Warnings

Not applicable at group level.

Pharmacodynamics

Chemical—no pharmacologic action as a class. In drug molecules, esters modulate lipophilicity, permeability, and clearance via esterase hydrolysis.

Mechanism of action

Reactivity proceeds via nucleophilic acyl substitution through a tetrahedral intermediate at the carbonyl carbon.

Absorption

Class effect in ADME: esterification typically increases lipophilicity; in vivo hydrolysis regenerates polar parents.

Volume of distribution / Protein binding / Metabolism / Elimination / Half-life / Clearance

Scaffold-dependent; hydrolytic metabolism (enzymatic/chemical) dominates.

Adverse Effects / Toxicity

Not intrinsic to the group; byproducts (released alcohol/acid) and rate of hydrolysis are scaffold-specific.

Pathways

High-yield transformations:

  • Hydrolysis: acid-catalyzed (reversible) or base-promoted saponification (irreversible to carboxylate)
  • Transesterification (acid or base)
  • Reduction: LiAlH₄ → primary alcohols; DIBAL-H (−78 °C) → aldehydes (from methyl/primary esters)
  • Grignard/organolithium addition: two equivalents → tertiary alcohols (via ketone stage)
  • Claisen condensation/Dieckmann (enolates of esters)
  • Aminolysis → amides (activation often helpful)
  • Acetalization of embedded carbonyls not typical; protection uses acyl derivatives instead

Pharmacogenomic Effects/ADRs

Not applicable to the group.

3. Interactions

Chemical Interactions

H-bond acceptor interactions with donors (proteins/solvents); Lewis base coordination at carbonyl oxygen; salt formation not typical unless hydrolyzed to acid.

Food Interactions

Not applicable (functional group).

4. Categories

ATC Codes

None (functional group)

Drug Categories

Functional group; Carboxylic acid derivative; Prodrug handle

Chemical Taxonomy

sp² carbonyl with alkoxy leaving group; resonance-stabilized acyl–oxygen framework; hydrolytic lability shaped by electronics/sterics and medium (acid/base/enzymes).

Affected organisms

Not applicable

5. Chemical Identifiers

UNII / CAS / InChI / InChIKey

Not applicable for the class.
Generic SMILES: R–C(=O)–OR′

IUPAC Name

Carboxylate ester functional group

6. References

IUPAC Gold Book — definitions and nomenclature of carboxylic esters.
Clayden, Greeves, Warren. Organic Chemistry — ester formation/hydrolysis, mechanisms (tetrahedral intermediate), Claisen condensation.
March’s Advanced Organic Chemistry — kinetics/thermodynamics of esterification and saponification; reduction chemistry (LiAlH₄, DIBAL-H).
Silverstein et al., Spectrometric Identification of Organic Compounds — IR (C=O ~1735 cm⁻¹; C–O 1050–1300 cm⁻¹), NMR assignments.
Carey & Sundberg. Advanced Organic Chemistry — acyl substitution, transesterification, and aminolysis strategies.

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