Please note there are a large number of isomers of molecular formula C₃H₆O₂ and this page presents a selection of them and where appropriate indicates the type of isomerism involved.

Initially I have chosen examples of isomers that pre-university students are most likely to come across, e.g. usually carboxylic acids, esters, aldehydes and ketones, but I have since added lots more out of curiosity!

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).

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) The chain variation is between e.g. C-C-C-O and C-O-C-C, and also include C=C and cyclic compounds, both alicyclic and heterocyclic.

(b) There is positional variation e.g. the hydroxy substituent in the aldehydes or enols.

(c) There are lots of examples of functional group isomerism e.g. carboxylic acids, esters, hydroxy-aldehydes, hydroxy-ketones, unsaturated alkene-alcohols (C=C + 2 x OH, 'enols'), in fact, every single isomer described is a functional group isomer of C3H6O2.

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 3D spatial variations that are not mirror images and not super imposable.

e.g. some of the alkene-alcohols (enols) exhibit E/Z (geometrical) isomerism as do some of the cyclic carbon ring molecules (alicyclic, propane based) and a few heterocyclic molecules give rings of 3 to 4 atoms of carbon and oxygen.

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.

e.g. some of the hydroxy-aldehydes and some of the alicyclic and heterocyclic ring compounds can exhibit R/S optical isomerism (i.e. form a pair of enantiomers).

3 CARBOXYLIC ACIDS and ESTERS (1) to (3)

(1) propanoic acid (propionic acid), , ,

Carboxylic acid functional group (COOH).

No E/Z or R/S isomerism possible

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

¹H NMR ratio of peaks: 3 : 2 : 1 (for equivalent protons)

Comparison of the infrared spectra of selected structural isomers of C₃H₆O₂

 

(2) methyl ethanoate (methyl acetate) , , , ,

Ester functional group. Made from ethanoic acid and methanol.

No E/Z or R/S isomerism possible

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

¹H NMR ratio of peaks: 3 : 3 = 1 : 1 (for equivalent protons)

Comparison of the infrared spectra of selected structural isomers of C₃H₆O₂

 

(3) ethyl methanoate, (ethyl formate), structural formulae ,  

displayed formula , skeletal formula

Ester functional group. Made from methanoic acid and ethanol.

No E/Z or R/S isomerism possible

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

¹H NMR ratio of peaks: 3 : 2 : 1 (for equivalent protons)

Comparison of the infrared spectra of selected structural isomers of C₃H₆O₂

 

Spectra links for isomers (1) to (3) which can be used to identify a specific isomer

The infrared spectrum of propanoic acid (propionic acid)

The infrared spectrum of methyl ethanoate (methyl acetate)

The infrared spectrum of ethyl methanoate (ethyl formate)

The mass spectrum of propanoic acid (propionic acid)

The mass spectrum of methyl ethanoate (methyl acetate)

The mass spectrum of ethyl methanoate (ethyl formate)

The H-1 NMR spectrum of propanoic acid (propionic acid)

The H-1 NMR spectrum of methyl ethanoate (methyl acetate)

The H-1 NMR spectrum of ethyl methanoate (ethyl formate)

The C-13 NMR spectrum of propanoic acid (propionic acid)

The C-13 NMR spectrum of methyl ethanoate (methyl acetate)

The C-13 NMR spectrum of ethyl methanoate (ethyl formate)

 

4 ALDEHYDES and KETONES (4) to (7)

(4) 2-hydroxypropanal, CH₃-CH(OH)-CHO 

Two functional groups: aldehyde (CHO) and alcohol (OH, hydroxyl, hydroxy)

This has a central chiral carbon (atom C2) and exhibits R/S isomerism.

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

¹H NMR ratio of peaks: 3 : 1 : 1 : 1 (for equivalent protons)

Comparison of the infrared spectra of selected structural isomers of C₃H₆O₂

 

(5)  3-hydroxypropanal, HO-CH₂-CH₂-CHO

Two functional groups: aldehyde (CHO) and alcohol (OH, hydroxyl/hydroxy)

Functional group isomer e.g. with carboxylic acid propanoic acid, and a positional isomer (OH).

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

¹H NMR ratio of peaks: 1 : 2 : 2 : 1 (for equivalent protons)

Comparison of the infrared spectra of selected structural isomers of C₃H₆O₂

 

(6) 2-methoxyethanal, CH₃OCH₂CHO

Two functional groups: aldehyde -CHO and ether linkage C-O-C.

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

¹H NMR ratio of peaks: 3 : 2 : 1 (for equivalent protons)

 

(7) 1-hydroxypropan-2-one, (1-hydroxypropanone), HO-CH₂-CO-CH₃

Two functional groups: ketone >C=O and alcohol (OH, hydroxy/hydroxyl).

Functional group isomer e.g. with carboxylic acid propanoic acid, and a positional isomer (OH).

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

¹H NMR ratio of peaks: 1 : 2 : 3 (for equivalent protons)

Comparison of the infrared spectra of selected structural isomers of C₃H₆O₂

 

5 ALKENE-DIOLS (8) to (12)

(8) prop-1-ene-1,1-diol, CH₃CH=C(OH)₂

Two functional groups: Two alcohol groups (2 x OH, a diol), and an alkene group (>C=C<)

A theoretical structure, doubt if it exists?

It is likely to be very unstable and lose water to form CH₃CH=C=O, CH₂=CH-CHO ?

Functional group isomer and positional isomer via positions of OH groups.

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

¹H NMR ratio of peaks: 3 : 1 : 2 (1+1) (for equivalent protons)

 

(9) prop-1-ene-1,2-diol,  CH₃C(OH)=CH-OH

Two functional groups: Two alcohol groups (2 x OH, a diol), and an alkene group (>C=C<)

Functional group isomer and a positional isomer (via OH group positions).

It exhibits E/Z (geometrical isomers) stereoisomerism via the >C=C< bond and ₈O has a higher priority than ₆C.

From the CIP assignment priority rule: ₈O > ₆C > ₁H  (about the >C=C< bond)

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

¹H NMR ratio of peaks: 3 : 1 : 1 : 1 (for equivalent protons)

Comparison of the infrared spectra of selected structural isomers of C₃H₆O₂

 

(10) prop-1-ene-1,3-diol, HOCH₂CH=CH-OH

Two functional groups: Two alcohol groups (2 x OH, a diol), and an alkene group (>C=C<)

Functional group isomer and a positional isomer (via OH group positions).

It exhibits E/Z (geometrical isomers) stereoisomerism via the >C=C< bond and ₈O has a higher priority than ₆C.

From the CIP assignment priority rule: ₈O > ₆C > ₁H  (about the >C=C< bond)

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

¹H NMR ratio of peaks: 1 : 2 : 1 : 1 : 1 (for equivalent protons)

Comparison of the infrared spectra of selected structural isomers of C₃H₆O₂

 

(11) prop-2-ene-1,2-diol, HOCH₂C(OH)=CH₂

Two functional groups: Two alcohol groups (2 x OH, a diol), and an alkene group (>C=C<)

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

¹H NMR ratio of peaks: 1 : 2 : 1 : 2 (for equivalent protons)

 

(12) prop-2-ene-1,1-diol, (HO)₂CHCH=CH₂

Two functional groups: Two alcohol groups (2 x OH, a diol), and an alkene group (>C=C<)

A theoretical structure, probably doesn't exist, likely to be very unstable and lose water to form CH₃CH=C=O or CH₂=CH-CHO ?

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

¹H NMR ratio of peaks: 2 (1+1) : 1 : 1 : 2 (for equivalent protons)

 

2 UNSATURATED ALCOHOL-ETHERS (enol-ethers)

(13) 1-methoxyethenol, CH₃OC(OH)=CH₂

Theoretical isomer, I don't think this exists?

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

¹H NMR ratio of peaks: 2 (1+1) : 1 : 3 (for equivalent protons)

 

(14) 2-methoxyethenol, CH₃OCH=CHOH

Theoretical structure, I think it does exist?

It exhibits E/Z (geometrical isomers) stereoisomerism via the >C=C< bond and ₈O has a higher priority than ₆C.

From the CIP assignment priority rule: ₈O > ₆C > ₁H  (about the >C=C< bond)

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

¹H NMR ratio of peaks: 3 : 1 : 1 : 1 (for equivalent protons)

 

3 ALICYCLIC COMPOUNDS based on cyclopropane (15) to (17) alicyclic ring compounds

(15) cyclopropane-1,1-diol, 1,1-dihydroxycyclopropane

Theoretical isomer, not sure if it exists.

Cyclo-alcohol structure, two alcohol functional groups, 2 x OH, so called a diol.

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

¹H NMR ratio of peaks: 4 (2+2) : 2 (1+1) (for equivalent protons)

 

(16)  cyclopropane-1,2-diol,1,2-dihydroxycyclopropane

Cyclo-alcohol structure, two alcohol functional groups, 2 x OH, so called a diol, which does exist.

This can exhibit both E/Z geometrical and R/S optical isomerism, this is a complex stereoisomerism situation and only dealt with at university level.

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

¹H NMR ratio of peaks: 2 : 2 (1+1) : 2 (1+1) (for equivalent protons)

 

(17) cyclopropylperoxide? name?

Theoretical isomer, not sure if it exists.

This has a hydroperoxide functional group (-OOH).

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

¹H NMR ratio of peaks: 4 (2+2) : 1 : 1 (for equivalent protons)

 

4 Theoretical UNSATURATED ALKENE-PEROXIDE COMPOUNDS (18) to (21) open chain, non-cyclic

See also (17above and 28, 29, 31 and 32 below)

(18) 1-propen-1-yl hydroperoxide, organic hydroperoxide, H-O-O-CH=CH-CH₃

Theoretical structure, exists? An organic hydroperoxide functional group.

Theoretically it exhibits E/Z (geometrical isomers) stereoisomerism via the >C=C< bond and ₈O has a higher priority than ₆C.

From the CIP assignment priority rule: ₈O₆C  >  ₁H₆C  >  ₁H  (about the >C=C< bond)

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

¹H NMR ratio of peaks: 1 : 1 : 1 : 3 (for equivalent protons)

 

(19) name?, organic hydroperoxide, H₂C=C(O-O-H)-CH₃

Theoretical structure, doubt if it exists?

An organic hydroperoxide functional group.

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

¹H NMR ratio of peaks: 2 : 1 : 3 (for equivalent protons)

 

(20) allyl hydroperoxide, 2-propen-1-yl hydroperoxide, H₂C=CH-CH₂-O-O-H

Not a 'theoretical' structure, and does exist.

An organic hydroperoxide functional group.

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

¹H NMR ratio of peaks: 2 : 1 : 2 : 1 (for equivalent protons)

 

(21) name?, organic peroxide, CH₃-O-O-CH=CH₂

Theoretical structure, doubt if it exists? An organic peroxide functional group.

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

¹H NMR ratio of peaks: 3 : 1 : 2 (for equivalent protons)

 

2 HYDROXY DERIVATIVES of OXETANE (22) to (23) heterocyclic ring compounds

(22) oxetan-2-ol - does exist

Two functional groups: cyclo-alcohol (secondary) and an ether linkage (C-O-C).

Exhibits R/S (optical) isomerism, the bottom right carbon is chiral and gives rise to a pair of enantiomers.

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

¹H NMR ratio of peaks: 2 : 2 : 1 : 1 (for equivalent protons)

 

(23) oxetan-3-ol - does exist

Two functional groups: cyclo-alcohol (secondary) and an ether linkage (C-O-C).

Plane of symmetry, so cannot exhibit R/S optical isomerism.

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

¹H NMR ratio of peaks: 4 (2+2) : 1 : 1 (for equivalent protons)

 

4 DERIVATIVES of 1,2-EPOXYETHANE and 1,2-EPOXYPROPANE (24) to (27)

(24) methoxy-1,2-epoxyethane, name?

Two ether function groups (C-O-C linkage), one aliphatic and one alicyclic.

Exhibits R/S (optical) isomerism, the bottom right ring carbon is chiral and gives rise to a pair of enantiomers.

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

¹H NMR ratio of peaks: 2 : 1 : 3 (for equivalent protons)

 

(25) 2-hydroxy-1,2-epoxypropane, (hydroxymethyl)oxirane, names?

exists?

Two functional groups: an alcohol (tertiary? OH) and a cyclic-ether linkage (C-O-C)

Exhibits R/S (optical) isomerism, the bottom right ring carbon is chiral and gives rise to a pair of enantiomers.

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

¹H NMR ratio of peaks: 2 : 3 : 1 (for equivalent protons)

 

(26) 3-hydroxy-1,2-epoxypropane or (oxiran-2-yl)methanol

Does exist.

Two functional groups: an alcohol (primary OH) and a cyclic-ether linkage (C-O-C)

Exhibits R/S (optical) isomerism, the bottom right ring carbon is chiral and gives rise to a pair of enantiomers.

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

¹H NMR ratio of peaks: 2 : 1 : 3 : 1 (for equivalent protons)

 

(27) 1-hydroxy-1,2-epoxypropane, name?

As far as I can tell it does exist.

Two functional groups: an alcohol (secondary OH) and a cyclic-ether linkage (C-O-C)

Exhibits R/S (optical) isomerism, both carbon atoms of the ring are chiral and gives rise to pairs of enantiomers.

BUT, the hydroxyl and methyl groups attached to the ring can adopt E/Z (geometrical) positions i.e. both above the plane of the ring or one above and one below the plane of the ring.

This 'overlap' of E/Z and R/S isomerism requires university level analysis!

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

¹H NMR ratio of peaks: 1 : 1 : 1 : 3 (for equivalent protons)

 

6 OTHER HETEROCYCLIC RING (C and O) COMPOUNDS

(28) ethyldioxirane, name?

An organic cyclic peroxide compound.

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

¹H NMR ratio of peaks: 1 : 2 : 3 (for equivalent protons)

 

(29) dimethyldioxirane

An organic cyclic peroxide compound.

A very symmetrical compound.

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

 

(30) methyl-1,3-dioxetane, name?

Does it exist?, cyclic ether (a double C-O-C linkage)

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

¹H NMR ratio of peaks: 2 : 1 : 3 (for equivalent protons)

 

(31) methyl-1,2-dioxetane, name ?

An organic cyclic peroxide compound.

A peroxide compound.

Can exhibit R/S optical isomerism, the bottom right carbon atom is a chiral centre (asymmetric).

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

¹H NMR ratio of peaks: 2 : 4 (2+2) (for equivalent protons)

 

(32) 1,2-dioxolane

An organic cyclic peroxide compound.

A peroxide compound.

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

¹H NMR ratio of peaks: 2 : 4 (2+2) (for equivalent protons)

 

(33) 1,3-dioxolane

exists, cyclic ether (a double C-O-C linkage)

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

¹H NMR ratio of peaks: 4 (2+2) : 2 (for equivalent protons)

 

Extra isomers of C₃H₆O₂ since writing the original page

(34) H₂C=CH-O-CH₂-OH, no idea how to name it or whether it exists, but university level molecule I think.

Interesting molecule which has three functional groups:

an alkene >C=C<, an ether C-O-C linkage and a primary alcohol group -CH₂-OH.

No E/Z or R/S isomerism, but a good example of functional group isomerism.

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

¹H NMR ratio of peaks: 2 : 1 : 2 : 1 (for equivalent protons)

This molecule was sent in by email from a SultanShihab, many thanks, keep them coming!

 

(35) ?

Keywords or phrases: how many isomers are there of molecular formula C3H6O2? how do you name the isomers of molecular formula C3H6O2? what is the molecular structure of the isomers of C3H6O2, what type of isomerism is exhibited by molecules of formula C3H6O2, how do you work out the isomers of molecular formula C3H6O2, what are the structural isomers of C3H6O2, the carbon chain isomers of C3H6O2 in the homologous series of alkanes, comparing the spectra of isomers of molecular formula C3H6O2 how many structural isomers of C3H6O2 can you draw? how many structural isomers does C3H6O2 have? what are the possible isomers of C3H6O2? revision notes on isomerism of C3H6O2 molecules, isomerism in aliphatic carboxylic acids, isomerism in aliphatic esters, carboxylic acid isomers of C3H6O2, ester isomers of C3H6O2, the molecular structure of the isomers of C3H6O2 how to draw the structural formula of isomers of C3H6O2, how to draw the displayed formula of isomers of C3H6O2, how to draw the skeletal formula of isomers of C3H6O2, how to name the isomers of molecular formula C3H6O2 R/S optical isomers enantiomers of C3H6O2 E/Z isomers cis trans stereoisomers of C3H6O2, isomers of C3H6O of molecular mass 74 Diagrams of the structure of the isomers of C3H6O2, Drawings the structural formula and skeletal formula of the isomers of C3H6O2, names of the isomers of C3H6O2, structural isomers are of C3H6O2, the number of carboxylic acid isomers of C3H6O2, number of ester isomers of C3H6O2, the alkene-alcohol enol isomers of C3H6O2, the alkene isomers of C3H6O2, alcohol isomers of C3H6O2? the aldehyde isomers of C3H6O2, the ketone isomers of C3H6O2, the any functional group isomers with a C3H6O2 the stereoisomers of C3H6O2, the E/Z geometrical isomers of C3H6O2, the R/S optical isomers (enantiomers) of C3H6O2