Empirical formula = molecular formula = C₃H₅XO₂ (where X = F, Cl, Br or I)

The isomers include halogen substituted carboxylic acids and esters, halogen and hydroxy substituted aldehydes and ketones and disubstituted alkenes (OH and X groups)

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.

(b) positional isomers e.g. position of halogen atoms or hydroxyl groups.

(c) many are functional group isomers e.g. acids versus esters, hydroxy aldehydes/ketones versus halogenated alkene diols.

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.

There is at least on case of a pair of E/Z geometrical isomers

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.

I've identified six isomers that can form R/S isomers (pairs of enantiomers).

 Note

In all formulae e.g. condensed structural formulae and images, X = F, Cl, Br or I

PLEASE NOTE: Some of these molecules may be too unstable to exist e.g. some of the iodo compounds, so arts of this page describe some 'theoretical' isomers of C₃H₅FO₂ , C₃H₅ClO₂ , C₃H₅BrO₂ and C₃H₅IO₂

(1) CH₃CHXCOOH, , condensed abbreviated formula, skeletal formula

Two functional groups: carboxylic acid (COOH) and halogen (X)

A halogen substituted carboxylic acid with an asymmetric carbon atom.

Carbon atom 2 is chiral, so R/S stereoisomers will exist (enantiomers, diagram below)

2-fluoropropanoic acid, 2-chloropropanoic acid, 2-bromopropanoic acid, 2-iodopropanoic acid

X = F, Cl, Br or I (and can be other groups like OH, but NOT H or CH₃ to exhibit R/S (optical) isomerism.

From the CIP priority rule: _ZX  >  ₈O₆C  >  ₆C  >  ₁H (Z = 9, 17, 35 and 53 for the halogens)

Indicating the R/S isomers e.g. (2S)-2-chloropropanoic acid, (R)-2-bromopropanoic acid etc.

e.g. 2-chloropropanoic acid , , ,

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

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

Index of ¹H NMR spectra organic compounds and Index of ¹³C NMR spectra organic compounds

 

(2) XCH₂CH₂COOH, , condensed abbreviated formula, skeletal formula

Two functional groups: carboxylic acid (COOH) and halogen (X)

A halogen substituted carboxylic acid.

3-fluoropropanoic acid, 3-chloropropanoic acid, 3-bromopropanoic acid, 3-iodopropanoic acid

e.g. 3-chloropropanoic acid , , ,

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

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

 

(3) HCOOCHXCH₃, , condensed abbreviated formula, skeletal formula

Two functional groups: ester (COOC) and halogen (X)

A halogen substituted ester.

R/S isomers because carbon atom 1 in the halo-ethyl group is chiral (asymmetric carbon atom).

1-fluoroethyl methanoate, 1-chloroethyl methanoate, 1-bromoethyl methanoate, 1-iodoethyl methanoate

Indicating the R/S isomers e.g. (R)-1-chloroethyl methanoate, (S)-1-bromoethyl methanoate

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

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

 

(4) HCOOCH₂CH₂X, , condensed abbreviated formula, skeletal formula

Two functional groups: ester (COOC) and halogen (X)

A halogen substituted ester.

2-fluoroethyl methanoate, 2-chloroethyl methanoate, 2-bromoethyl methanoate, 2-iodoethyl methanoate

2-fluoroethyl formate, 2-chloroethyl formate, 2-bromoethyl formate, 2-iodoethyl formate

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

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

 

(5) XH₂COOCH₃, , condensed abbreviated formula, skeletal formula

Two functional groups: ester (COOC) and halogen (X)

A halogen substituted ester.

methyl 2-fluoroethanoate, methyl 2-chloroethanoate, methyl 2-bromoethanoate, methyl 2-iodooethanoate

methyl 2-fluoroacetate, methyl 2-chloroacetate, methyl 2-bromoacetate, methyl 2-iodooacetate

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

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

 

(6) CH₃COOCH₂X, , condensed abbreviated formula, skeletal formula

Two functional groups: ester (COOC) and halogen (X)

A halogen substituted ester.

fluoromethyl ethanoate, chloromethyl ethanoate, bromomethyl ethanoate, iodomethyl ethanoate

fluoromethyl acetate, chloromethyl acetate, bromomethyl acetate, iodomethyl acetate

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

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

 

(7) XCOOCH₂CH₃, , condensed abbreviated formula, skeletal formula

Two functional groups: ester (COOC) and halogen (X)

ethyl fluoromethanoate, ethyl chloromethanoate, ethyl bromomethanoate, ethyl iodomethanoate

ethyl fluoroformate, ethyl chloroformate, ethyl bromoformate, ethyl iodoformate

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

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

 

(8) CH₃OCH₂COX, , condensed abbreviated formula, skeletal formula

Two functional groups: A methoxy (ether) substituted acyl halide (acid halide)

2-methoxyethanoyl fluoride, 2-methoxyethanoyl chloride, 2-methoxyethanoyl bromide, 2-methoxyethanoyl iodide

2-methoxyacetyl fluoride, 2-methoxyacetyl chloride, 2-methoxyacetyl bromide, 2-methoxyacetyl iodide

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

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

 

(9) XCH₂COCH₂OH, , condensed abbreviated formula, skeletal formula

Three functional groups: A di-substituted ketone, halogen group and alcohol group substituents in propanone.

1-fluoro-3-hydroxypropan-2-one, 1-chloro-3-hydroxypropan-2-one, 1-bromo-3-hydroxypropan-2-one, 1-iodo-3-hydroxypropan-2-one

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

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

 

(10) XCH₂CH(OH)CHO, , condensed abbreviated formula, skeletal formula

Three functional groups: A di-substituted aldehyde, halogen group and alcohol group substituents in propanal.

R/S isomers because carbon atom 2 is chiral.

3-fluoro-2-hydroxypropanal, 3-chloro-2-hydroxypropanal, 3-bromo-2-hydroxypropanal, 3-iodo-2-hydroxypropanal (or 2-hydroxy-3-iodopropanal)

Indicating the R/S isomers e.g. (R)-3-bromo-2-hydroxypropanal, (S)-3-chloro-2-hydroxypropanal

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

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

 

(11) HOCH₂CHXCHO, , condensed abbreviated formula, skeletal formula

Three functional groups: A di-substituted aldehyde, halogen group and alcohol group substituents in propanal.

R/S isomers because carbon atom 2 is chiral.

2-fluoro-3-hydroxypropanal, 2-chloro-3-hydroxypropanal, 2-bromo-3-hydroxypropanal, 2-iodo-3-hydroxypropanal

Indicating the R/S isomers e.g. (R)-2-chloro-3-hydroxypropanal, (S)-2-bromo-3-hydroxypropanal

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

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

 

(12) HOCHXCH=CHOH, , condensed abbreviated formula, skeletal formula

Two functional groups, 2 alcohol groups (diol) and an alkene group, an unsaturated alcohol.

3-fluoroprop-1-ene-1,3-diol, 3-chloroprop-1-ene-1,3-diol, 3-bromoprop-1-ene-1,3-diol, 3-iodoprop-1-ene-1,3-diol

There are E/Z isomers via the C=C bond and both, theoretically, have R/S isomers too because carbon atom 3 is chiral (asymmetric carbon atom).

Indicating the E/Z isomers e.g. (E)-3-chloroprop-1-ene-1,3-diol, (Z)-3-bromoprop-1-ene-1,3-diol

From the CIP priority rule: ₈O >  ₆C > ₁H (where X = halogen, and Z = 9, 17, 35 or 53)

This isomerism is very complex - university level.

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

¹H NMR ratio of peak areas: 1 : 1 : 1 : 1 : 1 (for equivalent protons)

 

(13) CH₂=CH-CX(OH)₂, , condensed abbreviated formula, skeletal formula

Two functional groups, 2 alcohol groups (diol) and an alkene group, an unsaturated alcohol.

Carbon atom 1 is chiral resulting in R/S isomers

1-fluoroprop-2-ene-1,1-diol, 1-chloroprop-2-ene-1,1-diol, 1-bromoprop-2-ene-1,1-diol, 1-iodoprop-2-ene-1,1-diol

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

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

BUT, for the 'end' =CH₂ alkene protons, you can get two chemical shifts close together, if there are two different groups attached to the other carbon of the C=C bond i.e. R"R'C=CH₂ where R" and R' are different. This causes the two =CH₂ protons to experience slightly different fields.

 

(14 onwards) There are lots more isomers of C₃H₅XO₂, despite what you might read on the internet!

There are definitely more halogenated alkene-diols like (12) and (13)

i.e. similar to (12) and (13), theoretically you can have 3-halocyclopropane-1,2-diol molecules that can exhibit both R/S and E/Z isomers - a case of complex stereoisomerism.

Similar to (9) HOCHX-CO-CH₃, which gives 1-halo-1-hydroxypropanone isomers

Similar to (10) HOCHX-CH₂-CHO, which gives 3-halo-3-hydroxypropanal isomers

Similar to (11) X-CH₂-CH(OH)-CHO, which gives 3-halo-2-hydroxypropanal isomers

You can also have theoretically, 3-halocyclopropane-1,2-diol isomers.

(?) Other isomers? If you spot any, let me know, I think there are quit a lot of them!

Functional Group Overview for selected isomers of C₃H₅FO₂ , C₃H₅ClO₂ , C₃H₅BrO₂ and C₃H₅IO₂

Applications by Molecular Formula

1. C₃H₅FO₂ – Fluorinated Compounds

• Carboxylic Acid (e.g., 2-fluoropropanoic acid):

  • Used in drug synthesis (e.g., fluorinated NSAIDs)

  • Intermediate in fluorinated agrochemicals

• Ester (e.g., methyl 2-fluoropropanoate):

  • Used in flavour and fragrance industry

  • Solvent in organic reactions

C₃H₅FO₂ – Fluoropropanoic Acid Isomers

Example Isomer: 2-Fluoropropanoic acid
Applications:

• Pharmaceuticals: Used as a precursor in the synthesis of antiviral and anticancer drugs, including intermediates for NSAIDs.

• Agrochemicals: Serves as a building block for herbicides, fungicides, and insecticides.

• Organic Synthesis: Acts as a reagent for introducing fluorine into molecules, enhancing metabolic stability and bioactivity.

• Fragrance & Flavour Industry: Used in the synthesis of aroma compounds.

• Solvent Use: Occasionally employed in specialized organic reactions.

2. C₃H₅ClO₂ – Chlorinated Compounds

• Carboxylic Acid (e.g., 2-chloropropanoic acid):

  • Used in herbicides and plant growth regulators

  • Intermediate in drug synthesis

• Ester (e.g., ethyl 2-chloropropanoate):

  • Used in flavouring agents and plasticizers

C₃H₅ClO₂ – Chloropropanoic Acid Isomers

Example Isomer: 2-Chloropropanoic acid
Applications:

• Pharmaceutical Intermediates: Used in the synthesis of drugs and fine chemicals.

• Agrochemicals: Functions as a precursor for herbicides and plant growth regulators.

• Organic Synthesis: Useful for preparing esters and amides.

• Industrial Chemicals: Involved in polymer and resin production.

• Caution: Corrosive and toxic; requires careful handling.

3. C₃H₅BrO₂ – Brominated Compounds

• Carboxylic Acid (e.g., 3-bromopropanoic acid):

  • Used in neurological research and metabolic studies

  • Intermediate in anticonvulsant drugs

• Ester (e.g., methyl 3-bromopropanoate):

  • Used in organic synthesis and specialty chemicals

C₃H₅BrO₂ – Bromopropanoic Acid Isomers

Example Isomers: 2-Bromopropanoic acid, 3-Bromopropanoic acid
Applications:

• Pharmaceuticals: Used in the synthesis of antihypertensives, sedatives, and antiepileptic drugs.

• Agrochemicals: Precursor for pesticides such as diflufenacil and furalax.

• Dyes & Polymers: Involved in the manufacture of specialty dyes and polymeric materials.

• Organic Synthesis: Introduces bromine functionality for further derivatization.

• Research: Studied for its potential in metabolic and neurological disorder treatments.

4. C₃H₅IO₂ – Iodinated Compounds

• Carboxylic Acid (e.g., 3-iodopropanoic acid):

  • Used in radiolabeling and medical imaging

  • Intermediate in iodinated drugs

• Ester (e.g., ethyl 3-iodopropanoate):

  • Applied in organic synthesis and radioactive tracers

C₃H₅IO₂ – Iodopropanoic Acid Isomers

Example Isomer: 3-Iodopropanoic acid
Applications:

• Pharmaceuticals: Intermediate in the synthesis of drugs targeting neurological and metabolic pathways.

• Agrochemicals: Used in the development of iodinated pesticides and herbicides.

• Materials Science: Applied in the production of polymers, resins, and specialty materials.

• Organic Synthesis: Valuable for introducing iodine into molecules, facilitating further functionalization.

• Research & Development: Widely used in chemical biology and medicinal chemistry labs.

Summary Table of some uses of selected isomers of C₃H₅FO₂ , C₃H₅ClO₂ , C₃H₅BrO₂ and C₃H₅IO₂

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

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