What Is (E)-2-butenoic acid

Content on WhatAnswers is provided "as is" for informational purposes. While we strive for accuracy, we make no guarantees. Content is AI-assisted and should not be used as professional advice.

Last updated: April 10, 2026

Quick Answer: (E)-2-butenoic acid, commonly known as crotonic acid, is an unsaturated monocarboxylic acid with the molecular formula C₄H₆O₂ and a molecular weight of 86.09 g/mol. The (E) designation indicates a trans configuration of the double bond, distinguishing it from its isomer (Z)-2-butenoic acid. This versatile chemical compound is used in polymer manufacturing, cosmetics, and industrial synthesis applications.

Key Facts

Molecular formula C₄H₆O₂ with molecular weight of 86.09 g/mol
Melting point of approximately 71-72°C and boiling point around 189°C
The (E) prefix indicates trans stereochemistry of the C=C double bond
Used extensively in production of polymers, plastics, and acrylic resins
Exhibits antimicrobial properties and is employed in cosmetic and skincare formulations

Overview

(E)-2-butenoic acid, more commonly recognized as crotonic acid, is an unsaturated monocarboxylic acid belonging to the class of α,β-unsaturated carboxylic acids. With the chemical formula C₄H₆O₂ and a molecular weight of 86.09 g/mol, this organic compound features a characteristic double bond between the second and third carbon atoms. The (E) designation specifically refers to the stereochemical configuration of this double bond, indicating that the substituents are positioned on opposite sides in a trans arrangement.

This naturally occurring compound, though produced in small quantities in nature, is primarily synthesized for industrial and commercial applications. Unlike its saturated counterpart butyric acid, crotonic acid possesses enhanced chemical reactivity due to its double bond conjugation with the carboxyl group. This conjugation creates an α,β-unsaturated system that makes it particularly valuable in organic synthesis and polymer chemistry. The compound exists as two geometric isomers: (E)-2-butenoic acid and its mirror image (Z)-2-butenoic acid, each with distinct physical and chemical properties.

How It Works

The molecular structure and reactivity of (E)-2-butenoic acid stem from its unique bonding arrangement and electronic properties:

Carboxyl Reactivity: The terminal carboxylic acid group (-COOH) enables esterification reactions, allowing formation of esters with alcohols, which is crucial for creating polymeric materials and specialty chemicals used in coatings and adhesives.
Double Bond Conjugation: The C=C double bond adjacent to the carboxyl group creates conjugation, increasing susceptibility to nucleophilic and electrophilic additions, making it reactive in polymerization and condensation reactions.
Stereochemical Specificity: The (E) configuration influences molecular geometry and intermolecular interactions, affecting crystallinity, solubility, and biological activity compared to the (Z) isomer, which has physical properties like a different melting point of around 30°C.
Polymerization Capability: The compound readily undergoes free-radical and ionic polymerization through its double bond, enabling synthesis of thermoplastics and specialty polymers with tailored properties for various industrial applications.
Antimicrobial Properties: The unsaturated structure and carboxylic acid functionality confer antimicrobial activity, inhibiting bacterial and fungal growth through disruption of cellular membranes and metabolic processes.

Key Comparisons

Property	(E)-2-Butenoic Acid	(Z)-2-Butenoic Acid	Butyric Acid (Saturated)
Melting Point	71-72°C	~30°C	-5.1°C
Boiling Point	~189°C	~180°C	163.3°C
Stereochemistry	Trans (E) configuration	Cis (Z) configuration	N/A (saturated)
Chemical Reactivity	Highly reactive (α,β-unsaturated)	Highly reactive (α,β-unsaturated)	Less reactive (saturated)
Primary Applications	Polymer synthesis, cosmetics	Chemical synthesis, research	Food additive, flavoring

Why It Matters

Industrial Polymer Production: (E)-2-butenoic acid serves as a critical monomer and precursor in manufacturing acrylic resins, copolymers, and specialty polymers used in adhesives, coatings, and composite materials across automotive and construction industries.
Cosmetic and Personal Care: The compound's antimicrobial properties and skin-compatibility make it valuable in cosmetic formulations, skincare products, and pharmaceutical applications where controlled microbial growth is essential.
Chemical Synthesis: Its reactive double bond and carboxylic acid functionality make it an important building block in organic synthesis, enabling production of pharmaceuticals, agrochemicals, and fine chemicals through various condensation and addition reactions.
Thermal Stability: With a boiling point of approximately 189°C, the compound maintains stability under moderate heating, making it suitable for high-temperature processing in industrial polymerization and synthesis procedures.

Understanding (E)-2-butenoic acid's structure and properties is fundamental to modern polymer chemistry and industrial organic synthesis. Its dual functionality—combining a reactive double bond with a carboxylic acid group—makes it an invaluable compound in creating advanced materials that meet demanding industrial specifications. As industries continue developing sustainable and high-performance polymers, the role of compounds like crotonic acid remains central to innovation in materials science and chemical manufacturing.