7 constitutional isomers of molecular formula C3H2F2, C3H2Cl2, C3H2Br2 & C3H2I2 condensed structural formula skeletal formula, IUPAC names, positional isomers, functional group isomerism isomers of C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2 uses properties applications Doc Brown's revision notes for advanced level organic chemistry courses

isomers of C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂

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Advanced level organic chemistry PART 14.7: Structural isomers of molecular formula C₃H₂X₂ (X = halogen)

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

The constitutional structural isomers of molecular formula C₃H₂X₂ (X = halogen)

[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 chemistry & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy and analysing the isomers of C₃H₂X₂ (X = halogen atom) [isomerism page updated Feb 18th 2026 *]

* Associated organic chemistry page links

* Index of sets of isomers for a given molecular formula

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

* email doc brown - comments - query? * [policies, cookies, disclaimer]

The constitutional-structural isomers of molecular formula C₃H₂X₂ (X = halogen, F, Cl, Br and I)

Relative molecular mass and percent composition by mass of C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂ based on atomic masses:

C 12.01, H 1.01, F 19.00, Cl 35.45, Br 79.90, I 126.90

Formula of compound	Relative molecular mass	% carbon	% hydrogen	% halogen
C₃H₂F₂	76.05	47.38	2.65	49.97
C₃H₂Cl₂	108.95	33.07	1.85	65.08
C₃H₂Br₂	197.85	18.21	1.02	80.77
C₃H₂I₂	291.85	12.35	0.69	86.96

Empirical formula = molecular formula = C₃H₂X₂ (where X = a single halogen atom)

Introduction to isomerism in molecules of formulae C₃H₂F₂ C₃H₂Cl₂ C₃H₂Br₂ C₃H₂I₂

If applicable (see isomerism summary at the end of the page)

7 constitutional isomers of formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2 skeletal formula structural formula of isomers of molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2

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 connectivity configuration, usually with significant differences in chemical and physical properties.

In terms of isomers of C₂H₂X₂ there are

(a) The carbon atoms can be a linear chain (aliphatic) or cyclic (alicyclic)

(b) Various position isomers based on the halogen substituent -X

(c) There is functional group isomerism - alkynes, dienes (allenes) and cycloalkenes.

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 C₂H₂X₂

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.

Two constitutional isomers exhibits R/S optical isomerism 4. and 6.

Note

Some of the C₃H₂X₂ isomers described may be highly reactive and very thermodynamically unstable e.g. due to weak highly strained bonds (e.g. strained ring, diiodo) and some may not even exist at all (except theoretically of course!).

Some of the images of C₃H₂X₂ isomers presented are theoretical, in the sense that some may be so unstable as not to exist, but you will find most, and sometimes all of them, on the internet.

The are 7 constitutional-structural isomers of molecular formula C₃H₂X₂ (X = F, Cl, Br and I), irrespective of any E/Z or R/S isomerism that may be possible.

Including the R/S optical isomers, the are 9 distinct isomers of molecular formula C₃H₂X₂

They are all open chain or cyclic aliphatic compounds derived from dihalo-substitution products of hydrocarbons with the formula C₃H₄ (propadiene, propyne or cyclopropene).

Details of the 7 constitutional structural isomers C₃H₂F₂ C₃H₂Cl₂ C₃H₂Br₂ C₃H₂I₂

(1) XCH₂C≡CX, , condensed constitutional formula, skeletal formula

1,3-difluoropropyne, 1,3-dichloropropyne,   1,3-dibromopropyne, 1,3-diiodopropyne

More correctly: 1,3-difluoroprop-1-yne,   1,3-dichloroprop-1-yne,   1,3-dibromoprop-1-yne,   1,3-diiodoprop-1-yne

Functional group isomer (e.g open chain alkyne versus cycloalkene) and positional isomer (X positions).

Two functional groups: alkyne (-C≡C-) and halogen (-X, X = F, Cl, Br and I)

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

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

(2) X₂CHC≡CH, , condensed constitutional formula, skeletal formula

Functional group isomer (e.g open chain alkyne versus cycloalkene) and positional isomer (X positions).

Two functional groups: alkyne (-C≡C-) and halogen (-X, X = F, Cl, Br and I)

3,3-difluoropropyne,   3,3-dichloropropyne,   3,3-dibromopropyne,   3,3-diiodopropyne

more correctly: 3,3-difluoroprop-1-yne,   3,3-dichloroprop-1-yne,   3,3-dibromoprop-1-yne,   3,3-diiodoprop-1-yne

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

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

(3) H₂C=C=CX₂, , condensed constitutional formula, skeletal formula

Functional group isomer (e.g open chain diene versus cycloalkene) and positional isomer (X positions).

Functional group alkene, actually a diene and halogen (-X, X = F, Cl, Br and I)

1,1-difluoropropadiene, 1,1-dichloropropadiene, 1,1-dibromopropadiene, 1,1-diiodopropadiene

1,1-difluoropropa-1,1-diene, 1,1-dichloropropa-1,1-diene, 1,1-dibromopropa-1,2-diene, 1,1-diiodopropa-1,2-diene

Old names: 1,1-difluoroallene,   1,1-dichloroallene,   1,1-dibromoallene,   1,1-diiodoallene

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

(4) XHC=C=CHX, , condensed constitutional formula, skeletal formula

Functional group isomer (e.g open chain diene versus cycloalkene) and positional isomer (X positions).

Functional group alkene, actually a diene and halogen (-X, X = F, Cl, Br and I)

1,3-difluoropropadiene, 1,3-dichloropropadiene, 1,3-dibromopropadiene, 1,3-diiodopropadiene

1,3-difluoropropa-1,2-diene, 1,3-dichloropropa-1,2-diene, 1,3-dibromopropa-1,2-diene1,3-diiodopropa-1,2-diene

Old names: 1,3-difluoroallene, 1,3-dichloroallene, 1,3-dibromoallene, 1,3-diiodoallene

These form stereoisomers because the pi orbitals of the two C=C=C bonds are at 90^o to each other and allows the formation of non-superimposable mirror image forms (a bit subtle at pre-university level, but make the models yourself!).

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

(5) , skeletal formula, two functional groups: cycloalkene and halogen.

Functional group isomer (e.g open chain alkyne versus cycloalkene) and positional isomer (X positions).

1,2-difluorocyclopropene,   1,2-dichlorocyclopropene,   1,2-dibromocyclopropene,   1,2-diiodocyclopropene

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

(6) , skeletal formula, functional groups: cycloalkene and halogen.

Functional group isomer (e.g open chain alkyne versus cycloalkene) and positional isomer (X positions).

The top carbon of the ∆ is asymmetric, and this chiral carbon allows the formation of R/S optical isomers.

1,3-difluorocyclopropene,   1,3-dichlorocyclopropene,   1,3-dibromocyclopropene,   1,3-diiodocyclopropene

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

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

(7) , skeletal formula, functional groups: cycloalkene and halogen.

Functional group isomer (e.g open chain alkyne versus cycloalkene) and positional isomer (X positions).

3,3-difluorocyclopropene,   3,3-dichlorocyclopropene,   3,3-dibromocyclopropene, 3,3-diiodocyclopropene

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

Spectra can be used to distinguish which halogen compound and which isomer

Summary of key points and extra notes on the isomers of molecular formulae

C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂

The C₃H₂X₂ compounds (X = F, Cl, Br, I) are dihaloalkenes (dienes)

Examples of types of isomerism for molecular formulae C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂

Type of Isomerism	Description	Example (IUPAC)
Structural positional Isomerism	Halogen atoms attached to different positions chain or ring	e.g 3,3-dichlorocyclopropene or 1,2-dichlorocyclopropene
Functional group isomerism	alkyne, diene, cycloalkene

Physical Property Differences for isomers of molecular formulae C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂

Property	Trends Across Halogens
Boiling Point	Increases from F → I
Dipole Moment	Decreases from F → I
Density	Increases with atomic mass
Solubility in Water	Decreases from F → I

Chemical Property Differences for isomers of molecular formulae C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂

Reaction Type	Reactivity
Nucleophilic Substitution	variable, depending on whether the halogen is attached to an unsaturated group - which often results in the halogen being less reactive.
Electrophilic Addition	alkynes tend to be more reactive than alkenes

Leaving group ability increases from F⁻ < Cl⁻ < Br⁻ < I⁻as the C-X bond gets weaker.

Uses and Applications of isomers of molecular formulae C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂

Common misconceptions about isomers of molecular formulae C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂

Assuming all isomers have same reactivity: Position and geometry affect both sterics and electronics.
Overlooking environmental concerns: Chlorinated and brominated alkenes may be toxic or persistent.

Exam Tips for questions involving for isomers of molecular formulae C₃H₂F₂, C₃H₂Cl₂, C₃H₂Br₂ and C₃H₂I₂

Use IUPAC naming: Number the chain to give the double bond and halogens the lowest locants.
Compare boiling points and dipole moments to explain physical trends.
Use displayed formulae to show positional and geometrical differences.
Watch for restricted rotation around C=C when predicting stereoisomers.

Learning objectives - questions to be answered?

How do you draw the structural formula and skeletal formula of the isomers of molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

How many aliphatic structural isomers are there of halogen compounds with molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

How many aliphatic carbon chain isomers are there of halogen compounds with molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

How many positional isomers are there of organic halogen molecules with molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

How many E/Z (geometrical) isomers are there of molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

How many R/S (optical) isomers (enantiomers) of molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

Are there any cyclic haloalkene isomers of formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

Are there any cyclo haloalkane isomers of formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

Are there any halodiene isomers of molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

Are there any haloalkyne isomers of molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

Are there any functional group isomers with a molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

Do C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2 organic halogen molecules have any stereoisomers?

Are there any E/Z (geometrical) isomers with a molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

Are there any R/S (optical) isomers (enantiomers) with a molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2?

Be able to deduce the isomers of organic halogen molecules with the formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2.

Be able to draw and name the substituted halogen compounds isomers of molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2.

Be able to deduce if the isomers of C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2 organic halogen compounds can exhibit R/S optical isomerism.

Be able to deduce if the isomers of C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2 can exhibit E/Z geometrical isomerism (do C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2 have cis/trans geometric isomers).

This page will answer these questions for molecular formula C3H2F2 C3H2Cl2 C3H2Br2 C3H2I2

Associated organic chemistry links

Index of sets of isomers for a given molecular formula

The molecular structure and naming of HALOALKANES (how to name and draw alkane structures)

The molecular structure and naming of ALKANES (how to name and draw alkane structures)

The molecular structure and naming of ALKENES (how to name and draw alkene structures)

Index of revision notes on the chemistry HALOALKANES including reactions

Advanced Level pre-university organic chemistry notes

IR, mass and H-1 and C-13 NMR spectra of organic compounds

For isomerism in organic chemistry, see also the notes

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

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

A summary chart of isomerism

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Examples of types of isomerism for molecular formulae C3H2F2, C3H2Cl2, C3H2Br2 and C3H2I2

Physical Property Differences for isomers of molecular formulae C3H2F2, C3H2Cl2, C3H2Br2 and C3H2I2

Chemical Property Differences for isomers of molecular formulae C3H2F2, C3H2Cl2, C3H2Br2 and C3H2I2

Uses and Applications of isomers of molecular formulae C3H2F2, C3H2Cl2, C3H2Br2 and C3H2I2