isomers of C2H4F2 , C2H4Cl2 , C2H4Br2 and C2H4I2

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Advanced level organic chemistry PART 14.7: Structural isomers of molecular formula C2H4X2 (X = halogen)

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

The structural isomers of molecular formula C2H4F2, C2H4Cl2, C2H4Br2 and C2H4I2

[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 C2H4X2 [isomerism page updated Feb 9th 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? * [privacy policy, cookies and disclaimer]

The constitutional-structural isomers of molecular formula C2H4F2 C2H4Cl2 C2H4Br2 and C2H4I2

Relative molecular mass and percent composition by mass of C2H4X2 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
C2H4F2 66.06 36.36 6.12 57.52
C2H4Cl2 98.96 24.27 4.08 71.65
C2H4Br2 187.86 12.79 2.15 85.06
C2H4I2 281.86 8.52 1.43 90.05

Empirical formula CH2X for molecular formula C2H4X2

Introduction to isomerism in molecules of formulae C2H4F2 C2H4Cl2 C2H4Br2 and C2H4I2

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

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

All the isomerism here is based on the relative positions of the substituent halogen atoms and no other isomerism is possible.

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. NOT possible for C2H4X2

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.

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.

Note

As far as I know, all of these isomers for the four molecular formulae exist.

The are only 2 possible constitutional-structural isomers of molecular formulae C2H4X2 (X = F, Cl, Br and I), and E/Z or R/S isomerism not possible.

They are all open chain aliphatic compounds derived from halogen dihalo-substitution products of the alkane hydrocarbon with the formula C2H6 (ethane)

Details of the 2 constitutional structural isomers C2H4F2 C2H4Cl2 C2H4Br2 C2H4I2

isomers of C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2 condensed structural formula skeletal formula constitutional formula

(1) CH3CHX2, 1,1-difluoroethane, 1,1-dichloroethane, 1,1-dibromoethane, 1,1-diiodoethane condensed constitutional structural formula skeletal formula , condensed structural formula and skeletal formula

1,1-difluoroethane, 1,1-dichloroethane, 1,1-dibromoethane, 1,1-diiodoethane

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

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

 

(2) XCH2CH2X, 1,2-difluoroethane, 1,2-dichloroethane, 1,2-dibromoethane, 1,2-diiodoethane condensed constitutional structural formula skeletal formula , condensed structural formula and skeletal formula

1,2-difluoroethane, 1,2-dichloroethane, 1,2-dibromoethane, 1,2-diiodoethane

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

Symmetrical molecule

Spectra can be used to distinguish which halogen compound and which isomer e.g.

The infrared spectrum of 1,1-dibromoethane

The infrared spectrum of 1,2-dibromoethane

The infrared spectrum of 1,1-dichloroethane

The infrared spectrum of 1,2-dichloroethane

The mass spectrum of 1,1-dibromoethane

The mass spectrum of 1,2-dibromoethane

The mass spectrum of 1,1-dichloroethane

The mass spectrum of 1,2-dichloroethane

The H-1 NMR spectrum of 1,1-dibromoethane

The H-1 NMR spectrum of 1,2-dibromoethane

The H-1 NMR spectrum of 1,1-dichloroethane

The H-1 NMR spectrum of 1,2-dichloroethane

The C-13 NMR spectrum of 1,1-dibromoethane

The C-13 NMR spectrum of 1,2-dibromoethane

The C-13 NMR spectrum of 1,1-dichloroethane

The C-13 NMR spectrum of 1,2-dichloroethane

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

C2H4F2, C2H4Cl2, C2H4Br2 and C2H4I2

The isomerism of C2H4X2 compounds (where X = F, Cl, Br, I), which are all dihaloethanes. These molecules exhibit structural (constitutional) isomerism, and their properties vary with halogen identity and substitution pattern.

Types of Isomerism for molecular formula C2H4F2, C2H4Cl2, C2H4Br2 and C2H4I2

Molecular Formula

Isomers

Type of Isomerism

IUPAC Names

C₂H₄F₂

2

Structural

1,1-difluoroethane and 1,2-difluoroethane

C₂H₄Cl₂

2

Structural

1,1-dichloroethane and 1,2-dichloroethane

C₂H₄Br₂

2

Structural

1,1-dibromoethane and 1,2-dibromoethane

C₂H₄I₂

2

Structural

1,1-diiodoethane and 1,2-diiodoethane

  • 1,1-isomers: Both halogen atoms on the same carbon.

  • 1,2-isomers: Halogen atoms on adjacent carbons.

No stereoisomerism (E/Z or R/S) is possible due to free rotation around single bonds and lack of chiral centres.

Physical Property Differences for molecular formula C2H4F2, C2H4Cl2, C2H4Br2 and C2H4I2

Property

1,1-Isomers

1,2-Isomers

Trends Across Halogens

Boiling Point

Slightly lower (more symmetrical)

Slightly higher (more polar)

Increases from F → I

Dipole Moment

Lower (symmetry cancels dipole)

Higher (asymmetry increases dipole)

Varies with electronegativity

Density

Slightly lower

Slightly higher

Increases with atomic mass

Solubility in Water

Lower

Slightly higher

Decreases from F → I

Chemical Property Differences for molecular formula C2H4F2, C2H4Cl2, C2H4Br2 and C2H4I2

Reaction Type

1,1-Isomers

1,2-Isomers

Nucleophilic Substitution

Slower (more steric hindrance)

Faster (less hindered)

Elimination Reactions

Less favourable

More favourable (β-H available)

Combustion

Similar

Similar

  • 1,2-isomers often undergo E2 elimination more readily due to accessible β-hydrogens.

  • Reactivity increases with halogen leaving group ability: I⁻ > Br⁻ > Cl⁻ > F⁻.

Uses and Applications for molecular formula C2H4F2, C2H4Cl2, C2H4Br2 and C2H4I2

Compound

Common Use

1,2-dichloroethane

Precursor to vinyl chloride (PVC production)

1,1-dichloroethane

Solvent, degreasing agent

1,2-dibromoethane

Lead scavenger in petrol (historical)

1,2-difluoroethane

Refrigerant (HFC-152a)

1,2-diiodoethane

Laboratory reagent (limited industrial use)

Common Misconceptions for molecular formula C2H4F2, C2H4Cl2, C2H4Br2 and C2H4I2

  • Mistaking positional isomers for stereoisomers: These are not stereoisomers; no restricted rotation or chiral centres.

  • Assuming identical reactivity: Position of halogens affects both steric and electronic environments.

  • Overlooking environmental impact: Heavier halogenated compounds (especially Cl and Br) may be ozone-depleting or toxic.

Exam Tips for questions involving molecular formula C2H4F2, C2H4Cl2, C2H4Br2 and C2H4I2

  • Always name isomers using IUPAC rules: number the chain to give halogens the lowest possible locants.

  • Watch for substitution versus elimination conditions in mechanisms.

  • Compare boiling points and dipole moments to explain physical trends.

  • Use skeletal or displayed formulae to clearly show isomeric differences.

  • Avoid confusing C₂H₄X₂ with C₂H₂X₂ (which can show E/Z isomerism due to the double bond).

Learning objectives - questions to be answered?

How do you draw the structural formula and skeletal formula of the isomers of molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

How many aliphatic structural isomers are there of halogen compounds with molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

How many aliphatic carbon chain isomers are there of halogen compounds with molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

How many positional isomers are there of organic halogen molecules with molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

How many E/Z (geometrical) isomers are there of molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

How many R/S (optical) isomers (enantiomers) of molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

Are there any cyclic haloalkene isomers of formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

Are there any cyclo haloalkane isomers of formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

Are there any halodiene isomers of molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

Are there any haloalkyne isomers of molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

Are there any functional group isomers with a molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

Do C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2 organic halogen molecules have any stereoisomers?

Are there any E/Z (geometrical) isomers with a molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

Are there any R/S (optical) isomers (enantiomers) with a molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2?

This page will answer these questions for molecular formula C2H4Cl2 C2H4Br2 C2H4F2 C2H4I2

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)

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

index for all isomerism pages

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. These organic chemistry revision notes are suitable for use of pre-university students studying AQA advanced level chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE advanced level chemistry, AP honors chemistry course, they will also prove useful to 1st year undergraduate students of chemistry

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