5 constitutional isomers of molecular formula C2H6O2, structural formula, functional group isomers, skeletal formula, IUPAAC names, positional isomers of C2H6O2 uses properties applications doc brown's advanced organic chemistry revision notes

isomers of C₂H₆O₂

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Advanced level organic chemistry PART 14.7: Constitutional structural isomers of molecular formula C₂H₆O₂

Doc Brown's Advanced Chemistry: Part 14.7: Isomers and extra notes on their properties and uses

The constitutional structural isomers of molecular formula C₂H₆O₂

[Author © Dr WP Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses, IB advanced chemistry & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy and analysing the isomers of C₂H₆O₂ [isomerism page updated Feb 9th 2026 *]

* Index of sets of isomers for a given molecular formula

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* Associated organic chemistry page links

* This is a big chemistry website, please allow time to explore

The 5 constitutional-structural isomers of molecular formula C₂H₆O₂

isomers of molecular formula C2H6O2, structural formula, skeletal formula, types of isomerism for molecular formula C2H6O2

Introduction to isomerism for molecular formula C₂H₆O₂ (see also isomerism summary diagram)

Percent mass composition by mass of C₂H₆O₂ based on the relative atomic masses

C= 12.01 H = 1.01 O = 16.00 and M_r(C₂H₆O₂) = 62.08

Element composition of C₂H₆O₂ by mass: 38.69% carbon * 9.76% hydrogen * 51.55% oxygen

Empirical formula CH₃O

Introduction to the constitutional structural isomers of molecular formula C₂H₆O₂

Structural isomerism - isomers based on different connectivity's of the constituent atoms, so cannot be spatially identical (but can be defined as having the same shape).

This includes (a) carbon chain variation (usually need a minimum of 4 C atoms), (b) change in position of a substituent or functional group and (c) functional group isomerism where the atoms have a different configuration, usually with significant differences in chemical and physical properties.

(a) applies if you count oxygen atoms as part of chain e.g. you can have O-C-C-O or C-O-C-O

(b) (OH group) and (c) ether/alcohol/peroxide functional groups apply to isomers of C₂H₆O₂

Stereoisomerism - isomers based on the same connectivity of the atoms, but 2D or 3D spatially different, non-superimposable images (e.g. E/Z isomers or mirror image R/S optical isomers)

This is where molecules have the same basic constitutional structural formula, but isomers differ in the 2D/3D arrangement of the atoms.

Does not apply to isomers of C₂H₆O₂ no chiral centre in these molecules

Note that:

There are only 5 constitutional isomers (as far as I can tell?), since no stereoisomerism is possible, it also means there are only 5 distinct structural isomers of molecular formula C₂H₆O₂

Some of these isomers are highly reactive and very unstable and some may not exist at all (except theoretically).

Details of five constitutional structural isomers of molecular formula C₂H₆O₂

(1) HOCH₂CH₂OH, ethane-1,2-diol (1,2-ethanediol, ethylene glycol)

A functional group structural isomer with two hydroxyl (alcohol, diol) groups in the molecule.

A functional group isomer (e.g. alcohol versus ether and it is also a positional group (OH) isomer with the 'theoretical' ethane-1,1-diol.

Symmetrical molecule

Number of low resolution NMR chemical shift δ signal peaks: 2 ¹H and 1 ¹³C (email if disagree?)

¹H NMR ratio of integrated chemical shift peak areas: 2 : 4 (for equivalent protons)

See also comparison of the infrared spectra of the 2 stable isomers of C₂H₆O₂

(2) CH₃OCH₂OH, methoxymethanol

Functional group structural isomer with one hydroxyl (alcohol) group and an ether C-O-C linkage in the molecule.

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 2 ¹³C (email if disagree?)

¹H NMR ratio of integrated chemical shift peak areas: 3 : 2 : 1 (for equivalent protons)

See also comparison of the infrared spectra of the 2 stable isomers of C₂H₆O₂

(3) CH₃OOCH₃, dimethyl peroxide

A functional group structural isomer with an -O-O- peroxide linkage in the molecule (isomeric with alcohols and ethers).

Symmetrical molecule.

Number of low resolution NMR chemical shift δ signal peaks: 1 ¹H and 1 ¹³C (email if disagree?)

(4) CH₃CH₂OOH, ethyl hydroperoxide

A functional group structural isomer with an -O-O- peroxide linkage in the molecule (isomeric with alcohols and ethers).

Number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 2 ¹³C (email if disagree?)

¹H NMR ratio of integrated chemical shift peak areas: 3 : 2 : 1 (for equivalent protons)

(5) CH₃CH(OH)₂, ethane-1,1-diol (1,1-ethanediol)

A functional group isomer (e.g. alcohol versus ether and it is also a positional group (OH) isomer with the ethane-1,2-diol.

As far as I know ethane-1,1-diol cannot be isolated?, if formed, it would be highly unstable and lose water to form ethanal (acetaldehyde)?

CH₃CH(OH)₂ ===> CH₃CHO + H₂O

This is typical of the instability of molecules with two hydroxyl groups attached to the same carbon atom.

However it is considered to be the hydrate of ethanal, the reverse of the equation above!

Theoretical number of low resolution NMR chemical shift δ signal peaks: 3 ¹H and 2 ¹³C (email if disagree?)

¹H NMR ratio of integrated chemical shift peak areas: 3 : 1 : 2 (1+1) (for equivalent protons)

Note that spectral analysis can help distinguish between isomers of C₂H₆O₂.

Summary of key points and extra notes on the isomers of molecular formula C₂H₆O₂.

This is a rich example for exploring isomerism in organic chemistry. The molecular formula C₂H₆O₂₂ corresponds to several isomers, each showcasing different types of structural (constitutional) isomerism, with implications for physical and chemical properties, and common exam pitfalls. Here's a structured breakdown tailored to your analytical style:

A comparison of the infrared (IR) spectral comparison of the stable isomers of C₂H₆O₂

The 2 stable isomers of C₂H₆O₂

Isomer Name	Structure	Functional Groups
Ethane-1,2-diol	HO–CH₂–CH₂–OH	2 × hydroxyl (–OH)
Methoxymethanol	CH₃–O–CH₂–OH	1 × hydroxyl, 1 × ether

Note: Ethane-1,1-diol (geminal diol) is unstable in isolation and typically exists transiently in aqueous aldehyde chemistry — so it's not usually tested as a stable isomer.

The peroxides are also unstable and not included in this infrared spectra analysis.

IR Spectral Comparison Table for the isomers of C₂H₆O₂

IR Region (cm⁻¹)	Ethane-1,2-diol	Methoxymethanol
3600–3200	Broad, intense OH stretch (strong H-bonding)	Narrower OH stretch (intramolecular H-bonding)
3000–2850	CH₂ symmetric/asymmetric stretch	CH₃ and CH₂ stretches
1450–1400	CH₂ scissoring + OH bend overtone	CH₂ bend + CH₃ deformation
1150–1050	Two strong C–O stretches (alcohols)	One C–O stretch (alcohol) + one C–O–C (ether)
950–750	CH₂ rock + C–C–O wag	CH₂ rock + C–O–C wag

Exam Revision Tips for the infrared spectra of the isomers of C₂H₆O₂

What to Focus On

OH Stretching Region (3600–3200 cm⁻¹)
- Ethane-1,2-diol: Very broad due to intermolecular H-bonding between two –OH groups.
- Methoxymethanol: Narrower due to intramolecular H-bonding with ether oxygen.
C–O Stretching (1050–1150 cm⁻¹)
- Alcohol C–O stretch is strong and sharp.
- Ether C–O–C stretch appears slightly higher (~1170 cm⁻¹) and is diagnostic for methoxymethanol.
Fingerprint Region (below 1500 cm⁻¹)
- CH₂ rocking and wagging modes differ subtly — useful for distinguishing isomers.

Quick Mnemonics

"OH = Overlap & Hydrogen bonding" → Broad OH = more H-bonding.
"Ether = Elevated C–O–C stretch" → Look near 1170 cm⁻¹.
"Diol = Double OH drama" → Expect two C–O stretches and a very broad OH band.

Common Misconceptions about the infrared spectra of isomers of C₂H₆O₂

Misconception	Correction
“All OH stretches look the same”	False — shape and position vary with H-bonding and environment.
“Ether and alcohol C–O stretches overlap”	Not always — ether C–O–C is typically higher and sharper.
“Broad OH = impurity or water”	Not necessarily — diols naturally show broad OH due to H-bonding.
“Geminal diols are always stable”	No — ethane-1,1-diol is unstable and rarely isolated.

Tips for Spectroscopy Questions involving the infrared spectra of isomers of C₂H₆O₂

If you're given an unknown IR spectrum and asked to identify the isomer:

Look first at the OH stretch: broad and intense → diol; sharp and narrow → monoalcohol.
Check for ether C–O–C stretch near 1170 cm⁻¹ — if present, it’s methoxymethanol.
Use the number of C–O stretches: two for diol, one alcohol + one ether for methoxymethanol.

Types of Isomerism in isomers of C₂H₆O₂

Isomer Name

Structure

Functional Groups

Type of structural isomerism

Ethane-1,2-diol

HO–CH₂–CH₂–OH

Diol (2 × –OH)

Functional group isomerism

Methoxymethanol

CH₃–O–CH₂–OH

Ether + Alcohol

Functional group isomerism

Ethane-1,1-diol

CH₃–CH(OH)₂

Geminal diol

Positional isomerism (OH groups on same C)

Dimethyl peroxide

CH₃–O–O–CH₃

Peroxide

Skeletal + functional group isomerism

Ethyl hydroperoxide

CH₃–CH₂–OOH

Hydroperoxide

Functional group isomerism

Differences in Physical Properties of isomers of C₂H₆O₂

Isomer

Boiling Point

Hydrogen Bonding

Volatility

Solubility in Water

Ethane-1,2-diol

High

Strong (2 × –OH)

Low

Very soluble

Methoxymethanol

Moderate

Moderate (1 × –OH)

Moderate

Soluble

Dimethyl peroxide

Low

None

High

Poor

Ethyl hydroperoxide

Low–Moderate

Weak (–OOH)

Moderate

Limited

Key Insight: Hydrogen bonding capacity strongly influences boiling point and solubility. Diols like ethylene glycol exhibit extensive intermolecular hydrogen bonding, raising boiling points and water solubility.

Differences in Chemical Properties of the isomers of C₂H₆O₂

Isomer

Reactivity

Typical Reactions

1,2-Ethanediol

Moderate

Oxidation to oxalic acid, esterification

Methoxymethanol

Moderate

Acid-catalyzed cleavage, oxidation

1,1-Ethanediol

Unstable, prone to dehydration

Converts to ethanal (acetaldehyde)

Dimethyl peroxide

Highly reactive, unstable

Radical decomposition, explosive tendencies

Ethyl hydroperoxide

Reactive oxidant

Oxidation of metals, radical initiator

Common Misconceptions about the isomers of C₂H₆O₂

Misidentifying functional groups: Students often confuse ethers and alcohols when both are present (e.g., methoxymethanol).
Assuming all isomers have similar boiling points: Overlooking the role of hydrogen bonding leads to incorrect predictions.
Neglecting peroxide stability: Dimethyl peroxide is rarely encountered due to its instability—yet it is a valid isomer.

Exam Tips for questions that may involve the isomers of C₂H₆O₂

Draw all isomers clearly, showing connectivity and functional groups.
Label functional groups explicitly—especially when mixed (e.g., alcohol + ether).
Compare boiling points using hydrogen bonding logic, not just molecular weight.
Use IUPAC naming conventions to avoid ambiguity.
Don't assume stereoisomerism—C₂H₆O₂ isomers lack any chiral centres or double bonds for E/Z or R/S forms.

The industrial relevance of C₂H₆O₂ isomers hinges on how their physical and chemical properties align with specific functional roles. Here's a breakdown of how each isomer’s characteristics influence its use (or avoidance) in industry:

Industrial Applications by isomer of C₂H₆O₂

Isomer

Key Properties

Industrial Use

Why It’s Chosen (or Avoided)

1,2-Ethanediol

High boiling point, strong H-bonding

Antifreeze ('ethylene glycol'), polyester production, heat transfer fluids

Low volatility, miscibility with water, stable diol structure

Methoxymethanol

Moderate polarity, mixed functional groups

Limited use; studied in astrochemistry and niche solvents

Less stable, mixed reactivity, not widely produced commercially

1,1-Ethanediol

Unstable geminal diol

Transient intermediate in aldehyde hydration

Too unstable for storage or bulk use; decomposes to acetaldehyde

Dimethyl peroxide

Highly reactive, explosive tendencies

Rarely used; potential radical initiator

Safety hazard—extreme instability and decomposition risk

Ethyl hydroperoxide

Reactive oxidant

Used in radical polymerization and oxidation reactions

Controlled use in small-scale synthesis; hazardous in bulk

Industrial implications of C₂H₆O₂ isomer properties

Boiling Point & Volatility: Ethylene glycol’s high boiling point makes it ideal for coolant systems and heat exchangers, where thermal stability is crucial.
Hydrogen Bonding: Enhances solubility and viscosity, important for polymer precursors like PET (polyethylene terephthalate).
Reactivity: Peroxides and hydroperoxides are used sparingly due to their explosive potential—they’re valuable in initiating radical reactions but require strict handling protocols.
Stability: Isomers like 1,1-ethanediol are too unstable for industrial storage, but they play a role in reaction mechanisms, especially in organic synthesis and biochemical pathways.

Exam Insight and Misconceptions about the isomers of C₂H₆O₂

Misconception: Students may assume all isomers are equally viable for industrial use. In reality, stability and safety are decisive.
Tip: When asked about industrial applications, always link structure → property → function. For example, ethylene glycol’s two –OH groups enable hydrogen bonding, which supports its role in antifreeze.

Learning objectives - questions to be answered?

How many constitutional structural isomers are there of molecular formula C2H6O2?

Are there any positional isomers of molecular formula of C2H6O2?

Are there any E/Z (cis/trans) geometrical isomers of molecular formula C2H6O2?

Are there any R/S optical isomers of molecular formula C2H6O2?

How do you draw the skeletal structure of isomers of molecular formula C2H6O2?

How do you draw the structural formula of the isomers of molecular formula C2H6O2?

Can you recognise the different functional groups in the isomers of molecular formula C2H6O2?

How do you name the isomers of molecular formula C2H6O2?

This page will answer these questions for molecular formulae C2H6O2

A summary chart of isomerism

Associated organic chemistry links

Index of sets of isomers for a given molecular formula

Isomerism: introduction, structural isomerism - chain, positional, functional group, tautomerism

Stereoisomerism: introduction, definition, priority rules, E/Z isomerism (cis/trans isomerism)

Stereoisomerism - R/S isomerism (optical isomerism) - definition - examples explained

The molecular structure and naming of ALKENES

The molecular structure and naming of aliphatic ALCOHOLS including isomeric ethers

The molecular structure and Naming of ALDEHYDES and KETONES

Index of all IR, mass, 1H NMR and 13C NMR spectroscopy pages

This is a big chemistry website, please allow time to explore

Index of advanced (pre-university) organic chemistry revision notes

The chemistry of alkanes and the petrochemical industry

The chemistry of alkenes

The chemistry of organic halogen compounds

The chemistry of alcohols

The chemistry of aldehydes and ketones

The chemistry of carboxylic acids and derivatives

The chemistry of organo-nitrogen compounds

The chemistry of aromatic compounds

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The 2 stable isomers of C2H6O2

IR Spectral Comparison Table for the isomers of C2H6O2

Exam Revision Tips for the infrared spectra of the isomers of C2H6O2

What to Focus On

Quick Mnemonics

Common Misconceptions about the infrared spectra of isomers of C2H6O2

Tips for Spectroscopy Questions involving the infrared spectra of isomers of C2H6O2

Types of Isomerism in isomers of C2H6O2

Differences in Physical Properties of isomers of C2H6O2

Differences in Chemical Properties of the isomers of C2H6O2

Common Misconceptions about the isomers of C2H6O2

Exam Tips for questions that may involve the isomers of C2H6O2

Industrial Applications by isomer of C2H6O2

Industrial implications of C2H6O2 isomer properties

Exam Insight and Misconceptions about the isomers of C2H6O2