11 constitutional isomers of formula C3H8O2 isomerism of molecular formula C3H8O2 structural formula & names of isomers molecules stereoisomers functional group isomers skeletal formula of isomers of C3H8O2 uses applications doc brown's advanced organic chemistry revision notes

isomers of C₃H₈O₂

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Advanced level organic chemistry PART 14.7: Structural isomers of molecular formula C₃H₈O₂

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

Structural isomers and stereoisomers of molecular formula C₃H₈O₂

[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 and US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy and analysing the isomers of C₃H₈O₂ [updated Feb 18th 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

11 Selected constitutional-structural isomers of molecular formula C₃H₈O₂

Percent mass composition of C₃H₈O₂ based on the relative atomic masses

C= 12.01 H = 1.01 O = 16.00 and M_r(C₃H₈O₂) = 76.11

Element composition of C₃H₈O₂ by mass: 47.33% carbon * 10.61% hydrogen * 42.06% oxygen

Empirical formula = molecular formula C₃H₈O₂

Introduction to isomerism for molecular formula C₃H₈O₂ (see also isomerism summary diagram)

isomers of molecular formula C3H8O, structural formula, skeletal formula, types of isomerism for molecular formula C3H8O2

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 atoms), (b) change in position of a substituent or functional group and (c) functional group isomerism where the atoms have a different connectivity configuration, usually with significant differences in chemical and physical properties.

(a) You do get variation of the chain in terms of C and O e.g. C-C-C-O or C-C-O-C

(b) Positional isomers from difference in -OH and -OOH substituent positions

(c) Functional group isomers, diols versus ethers versus peroxides

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.

E/Z stereoisomerism was called 'geometrical isomerism' e.g. cis and trans isomers of alkenes or disubstituted cyclic alkanes where there are 2D/3D spatial variations that are not mirror images and not super imposable.

Not possible for C₃H₈O₂

R/S stereoisomerism was called 'optical isomerism', the pairs of isomers are called enantiomers which are 3D non-superimposable mirror image forms of the molecule. The molecule must have a chiral centre (a stereocentre), that is an asymmetric carbon atom with four different atoms/groups attached to it.

Does apply to isomers C2 for 2 and C1 5 are chiral (asymmetric) carbon atoms giving two pairs of enantiomers for C₃H₈O₂

Note

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

I've identified 11 constitutional isomers (actual & theoretical).

So, including the R/S enantiomer pairs means I've identified 13 distinct isomers.

Details of the isomers of molecular formula C3H8O2

4 DIOLS based on propane (1) to (4)

(1) CH₃CH₂CH(OH)₂, propane-1,1-diol (1,1-propanediol)

A functional group structural isomer (alcohol, diol) and a positional isomer based on the positions of the hydroxyl groups.

One of four positional isomers based on pairs of OH hydroxyl groups.

Having two hydroxyl groups on the same carbon atom will make this a very unstable molecule, so I'm not sure if it exists?

Theoretical number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 3 ¹³C (email if disagree?)

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

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

(2) HOCH₂CH(OH)CH₃, propane-1,2-diol (1,2-propanediol)

A functional group structural isomer (alcohol, diol) and a positional isomer based on the positions of the hydroxyl groups.

One of four positional isomers based on pairs of OH hydroxyl groups.

This will exhibit R/S (optical) isomerism, carbon atom 2 is a chiral stereocentre (asymmetric carbon).

From the CIP assignment priority rule for R/S isomers: ₈O > ₆C₈O > ₆C₆C > ₆C₁H

Number of low resolution NMR chemical shift δ signal peaks: 5 ¹H and 3 ¹³C (email if disagree?)

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

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

(3) HOCH₂CH₂CH₂OH, propane-1,3-diol (1,3-propanediol)

A functional group structural isomer (alcohol, diol) and a positional isomer based on the positions of the hydroxyl groups.

One of four positional isomers based on pairs of OH hydroxyl groups.

A symmetrical molecule.

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: 2 : 4 : 2 (for equivalent protons)

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

(4) CH₃C(OH)₂CH₃, propane-2,2-diol (2,2-propanediol)

A functional group structural isomer (alcohol, diol) and a positional isomer based on the positions of the hydroxyl groups.

One of four positional isomers based on pairs of OH hydroxyl groups.

A very symmetrical molecule.

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

¹H NMR ratio of integrated chemical shift peak areas: 6 : 2 (for equivalent protons)

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

4 ALKOXY ALCOHOLS and ETHERS (5) to (8)

(5) CH₃CH(OH)OCH₃, 1-methoxyethanol

A functional group structural isomer with hydroxyl group (alcohol) and a C-O-C ether linkage.

This will exhibit R/S (optical) isomerism, carbon atom 1 is a chiral stereocentre (asymmetric carbon).

From the CIP assignment priority rule for R/S isomers: ₈O₆C > ₈O₁H > ₆C₆C > ₆C₁H

Theoretical number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 3 ¹³C (email if disagree?)

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

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

(6) CH₃OCH₂CH₂OH, 2-methoxyethanol

A functional group structural isomer with a hydroxyl group (alcohol) and a C-O-C ether linkage.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 3 ¹³C (email if disagree?)

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

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

(7) CH₃OCH₂OCH₃, dimethoxymethane

A functional group structural isomer a double C-O-C ether linkage.

A symmetrical molecule.

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

¹H NMR ratio of integrated chemical shift peak areas: 6 : 2 (for equivalent protons)

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

(8) CH₃CH₂OCH₂OH, ethoxymethanol

A functional group structural isomer with a hydroxyl group, primary alcohol group and a C-O-C ether linkage.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 3 ¹³C (email if disagree?)

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

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

3 PEROXIDES (9) to (11)

(9) CH₃CH₂OOCH₃, ethyl methyl peroxide

A functional group structural isomer, with an organic -O-O- peroxide linkage.

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

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

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

(10) CH₃CH₂CH₂OOH, propyl hydroperoxide

A functional group structural isomer, with a -O-O- peroxide linkage.

Its a positional (-OOH) isomer with isopropyl hydroperoxide.

Number of low resolution NMR chemical shift δ signal peaks: 4 ¹H and 3 ¹³C (email if disagree?)

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

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

(11) (CH₃)₂CHOOH, isopropyl hydroperoxide

A functional group structural isomer, with a -O-O- peroxide linkage.

Its a positional (-OOH) isomer with propyl hydroperoxide.

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: 6 : 1 : 1 (for equivalent protons)

Comparison of prominent wavenumber absorptions of the infrared spectra of isomers of C₃H₈O₂

Comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

Note that spectral analysis can help distinguish between isomers of C₃H₈O₂

Summary of key points and extra notes on the isomers of molecular formula C₃H₈O₂

Molecules with the formula C₃H₈O₂ (e.g. propanediols, methoxyethanols, peroxides) exhibit a rich variety of isomerism. Here's a structured breakdown tailored to your analytical style:

Types of isomerism in C₃H₈O₂ Isomers

Isomerism Type	Description	Examples
Structural Isomerism	Same molecular formula, different connectivity of atoms	1,2-Propanediol versus 1,3-Propanediol
→ Chain Isomerism	Variation in carbon backbone	Rare in C₃H₈O₂ due to short chain
→ Functional Isomerism	Different functional groups	Diols versus ethers versus peroxides
→ Position Isomerism	Same functional group, different position	OH on C1 versus C2 versus C3
→ Metamerism	Different alkyl groups around ether/peroxide link	CH₃-O-CH₂CH₂ versus CH₃CH₂-O-CH₂
Stereoisomerism	Same connectivity, different spatial arrangement	(R)/(S)-1,2-Propanediol
→ Optical Isomerism	Chiral centres lead to enantiomers	1,2-Propanediol (chiral at C2)

Differences in Physical Properties of the isomers of C₃H₈O₂

Property	Diols (e.g. 1,2-Propanediol)	Ethers (e.g. 2-Methoxyethanol)	Peroxides
Boiling Point	High (due to H-bonding)	Moderate	Lower (less H-bonding)
Solubility in Water	Very soluble	Soluble	Variable
Viscosity	High	Lower	Lower
Density	Slightly higher	Moderate	Lower

Optical isomers have identical physical properties except for how they rotate plane-polarized light.

Differences in Chemical Properties of the isomers of C₃H₈O₂

Reactivity	Diols	Ethers	Peroxides
Oxidation	Can form aldehydes/ketones	Relatively stable	Highly reactive, radical source
Esterification	Forms diesters	Forms monoesters	Less common
Dehydration	Can form cyclic ethers or alkenes	Less prone	Unstable under heat
Acid/Base Reaction	Weakly acidic OH groups	Inert	May decompose

Stereoisomers may differ in enzyme reactivity or biological activity.

Common Misconceptions involving the isomers of C₃H₈O₂

“All isomers have similar properties” → False. Functional group changes drastically affect boiling point, reactivity, and solubility.
“Optical isomers are always easy to identify” → Not unless there's a chiral center and no internal symmetry.
“C₃H₈O₂ only forms diols” → It can also form ethers, peroxides, and hemiacetals.

Exam Tips for questions involving the isomers of C₃H₈O₂

Always draw full structures to spot functional and positional isomers.
Check for chirality: Look for tetrahedral carbons with four different groups.
Use boiling point trends to justify physical property differences.
Link functional groups to reactions: Diols → oxidation; ethers → cleavage; peroxides → radical reactions.
Watch out for overlooked isomers like geminal diols or hemiacetals.

A comparison of the prominent wavenumber absorptions of the infrared spectra of the isomers of C₃H₈O₂

A comparative summary of the prominent IR absorption bands for the main isomeric types of C₃H₈O₂, including alcohols, ethers, peroxides, and hydroperoxides. These functional groups exhibit distinct vibrational modes in the IR spectrum, allowing differentiation.

Reminder of isomer types of C₃H₈O₂ and their functional groups relevant to their infrared spectra

Isomer Type	Example Compound	Functional Groups
Alcohols	1,2-Propanediol	Two –OH groups
Ethers	Methoxyethanol	–OH and –O–CH₃
Peroxides	Methyl hydroperoxide	–O–O– and –CH₃
Hydroperoxides	2-Hydroperoxypropanol	–OOH and –OH

IR Spectral Comparison: Prominent Wavenumbers of the infrared spectra of the isomers of C₃H₈O₂

Functional Group	Stretching Mode	Typical Wavenumber (cm⁻¹)	Notes
O–H (alcohol)	Broad stretch	3200–3600	Broad due to H-bonding
C–O (alcohol/ether)	Stretch	1000–1150	Sharp, medium intensity
C–H (alkyl)	Stretch	2850–2960	Common to all isomers
O–O (peroxide)	Stretch	~850	Weak, diagnostic for peroxides
O–H (hydroperoxide)	Broad stretch	~3350	Very broad, hydrogen bonded
O–O–H (hydroperoxide)	Bend/stretch combo	~877	Weak, but characteristic

Tips for interpreting the infrared spectra of the isomers of C₃H₈O₂

Alcohols show broad O–H stretches and strong C–O stretches. Diols may show broader bands due to intramolecular hydrogen bonding.
Ethers lack O–H stretch (unless combined with alcohol) and show C–O stretches near 1100 cm⁻¹.
Peroxides are identified by a weak O–O stretch near 850 cm⁻¹, often overlooked without context.
Hydroperoxides exhibit both O–H and O–O stretches, with the O–H being very broad and intense, and the O–O appearing as a weak band near 877 cm⁻¹.

A comparison of the prominent diagnostic ions of the mass spectra of the isomers of C₃H₈O₂

A comparative summary of the diagnostic mass spectral fragments (m/z values) for the major isomer types of C₃H₈O₂, including alcohols, ethers, peroxides, and hydroperoxides. These fragments arise from characteristic cleavage patterns and losses during electron ionization.

Isomer Types of C₃H₈O₂ and Fragmentation Behavior

Isomer Type	Example Compound	Functional Groups	Molecular Ion (M⁺)
Alcohols	1,2-Propanediol	Two –OH groups	m/z = 76
Ethers	Methoxyethanol	–OH and –O–CH₃	m/z = 76
Peroxides	Methyl hydroperoxide	–O–O– and –CH₃	m/z = 76
Hydroperoxides	2-Hydroperoxypropanol	–OOH and –OH	m/z = 76

Diagnostic Fragment Ions (m/z) by Isomer type for the mass spectra of C₃H₈O₂ isomers

Isomer Type	Key Fragment Ions (m/z)	Fragment Description	Notes
Alcohols	31	CH₂OH⁺	Common base peak
	59	C₃H₇O⁺ (loss of H•)	Seen in propan-1-ol
	42	C₃H₆⁺ (loss of H₂O)	Dehydration peak
Ethers	45	CH₃OCH₂⁺ or CH₃CH₂O⁺	α-cleavage next to ether oxygen
Ethers	31	CH₂OH⁺ (if –OH present)	Only in hydroxy ethers
Peroxides	61	Loss of CH₃• from methyl hydroperoxide	Weak molecular ion, unstable
Peroxides	31	HO₂⁺ or CH₃O⁺ depending on cleavage	O–O bond cleavage dominates
Hydroperoxides	59	C₃H₇O⁺ (loss of HO• or H•)	Similar to alcohols
Hydroperoxides	33 or 17	HO₂+ or OH⁺	O–O–H fragmentation

Interpretation tips for the mass spectra of the isomers of C₃H₈O₂

Alcohols often show m/z 31 (CH₂OH⁺) and m/z 59, with M–18 (loss of H₂O) being common.
Ethers fragment via α-cleavage, giving alkoxy ions like CH₃O⁺ or CH₃CH₂O⁺
Peroxides have weak molecular ions and fragment via O–O bond cleavage, producing HO₂⁺ or CH₃O⁺
Hydroperoxides show combined alcohol and peroxide fragmentation, with m/z 33–47 being diagnostic.

Learning objectives - questions to be answered?

How many constitutional structural isomers are there of molecular formula C3H8O2?

Are there any positional isomers of molecular formula of C3H8O2?

Are there any E/Z (cis/trans) geometrical isomers of molecular formula C3H8O2?

Are there any R/S optical isomers of molecular formula C3H8O2?

How do you draw the skeletal structure of isomers of molecular formula C3H8O2?

How do you draw the structural formula of the isomers of molecular formula C3H8O2?

Can you recognise the different functional groups in the isomers of molecular formula C3H8O2?

How do you name the isomers of molecular formula C3H8O2?

This page will answer these questions for molecular formulae C3H8O2

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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Types of isomerism in C3H8O2 Isomers

Differences in Physical Properties of the isomers of C3H8O2

Differences in Chemical Properties of the isomers of C3H8O2

Common Misconceptions involving the isomers of C3H8O2

Exam Tips for questions involving the isomers of C3H8O2

Reminder of isomer types of C3H8O2 and their functional groups relevant to their infrared spectra

IR Spectral Comparison: Prominent Wavenumbers of the infrared spectra of the isomers of C3H8O2

Tips for interpreting the infrared spectra of the isomers of C3H8O2

Isomer Types of C3H8O2 and Fragmentation Behavior

Diagnostic Fragment Ions (m/z) by Isomer type for the mass spectra of C3H8O2 isomers

Interpretation tips for the mass spectra of the isomers of C3H8O2