isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2

Advanced level organic chemistry PART 14.7: Constitutional isomers of molecular formula C3H6X2 (X = halogen)

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

For the structural isomers of molecular formula C3H6X2 (X = halogen F, Cl, Br and I)

[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 C3H6X2 [updated Dec 16th 2025]

 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] 

The constitutional-structural isomers of molecular formulae C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2

Relative molecular mass and percent composition of C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2 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
C3H6F2 80.09 44.99 7.57 47.44
C3H6Cl2 112.99 31.89 5.36 62.75
C3H6Br2 201.89 17.85 3.00 79.15
C3H6I2 295.89 12.18 2.05 85.77

Empirical formula = molecular formula = C3H6X2

Introduction to isomerism in molecules of formulae  C3H6F2  C3H6Cl2  C3H6Br2  and  C3H6I2

4 constitutional isomers of C3H6F2, C3H6Cl2, C3H6Br2 or C3H6I2 structural isomers skeletal formula isomers names

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 (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.

Only (b) applies to C3H6X2 due to the different positions of the two halogen atoms.

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.

E/Z geometrical isomerism not possible here.

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.

One isomer exhibits R/S optical isomerism No. (9)(d)

The 1,2-dihalopropanes exhibit R/S (optical) isomerism, C2 is chiral.

Note

Some of the C3H6F2  C3H6Cl2  C3H6Br2  and  C3H6I2 isomers described may be highly reactive and very thermodynamically unstable e.g. due to weak highly strained bonds and some may not even exist at all (except theoretically of course!). I think in this case they all stable!

Some of the images of the C3H6X2 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 only 4 constitutional-structural isomers of molecular formula C3H6X2 (X = F, Cl, Br and I), irrespective of any E/Z or R/S isomerism that may be possible.

The one case of R/S 'optical' isomerism means there are actually 5 distinct isomers in total per C3H6X2 formula.

They are all open chain aliphatic compounds derived from halogen di-substitution products of the alkane hydrocarbon propane with the formula C3H8

Details of the four constitutional structural isomers of formulae  C3H6F2  C3H6Cl2  C3H6Br2  and  C3H6I2

They are all dihalopropane structural positional isomers based on the disposition of the two halogen atoms.

Only the 1,2-dihalopropanes can exhibit R/S (optical isomerism) making a total of five distinct isomers in total.

 

(1) CH3CH2CHX2, 1,1-difluoropropane, 1,1-dichloropropane, 1,1-dibromopropane, 1,1-diiodopropane structural formula skeletal formula , abbreviated constitutional formula, displayed formula and skeletal formula

1,1-difluoropropane,  1,1-dichloropropane,  1,1-dibromopropane, 1,1-diiodopropane

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)

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

 

(2) CH3CHXCH2X, 1,2-difluoropropane, 1,2-dichloropropane, 1,2-dibromopropane, 1,2-diiodopropane structural formula skeletal formula , abbreviated constitutional formula, displayed formula and skeletal formula

1,2-difluoropropane,  1,2-dichloropropane,  1,2-dibromopropane, 1,2-diiodopropane

(R)-1,2-difluoropropane,  (R)-1,2-dichloropropane,  (R)-1,2-dibromopropane, (R)-1,2-diiodopropane

(S)-1,2-difluoropropane,  (S)-1,2-dichloropropane,  (S)-1,2-dibromopropane, (S)-1,2-diiodopropane

These molecules exhibit R/S optical isomerism (names above), the middle carbon atom 2 is chiral (asymmetric) with four different atoms/groups attached to it, so can form two non-superimposable mirror images forms (the pair of enantiomers are illustrated below).

R and S 'optical' isomers of 1,2-difluoropropane, 1,2-dichloropropane, 1,2-dibromopropane, 1,2-diiodopropane S & R 'optical' isomers of CH3CHXCH2X

From the CIP assignment priority rule: ZX > ZX6C > 1H6C > 1H (where X = halogen, and Z = 9, 17, 35 or 53)

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)

 

(3) XH2CCH2CH2X, 1,3-difluoropropane, 1,3-dichloropropane, 1,3-dibromopropane, 1,3-diiodopropane structural formula skeletal formula , abbreviated constitutional formula, displayed formula and skeletal formula

1,3-difluoropropane,  1,3-dichloropropane,  1,3-dibromopropane, 1,3-diiodopropane

Symmetrical molecule, so, reduces the number of NMR chemical shifts resonances.

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 = 2 : 1  (for equivalent protons)

 

(4) CH3CX2CH3, 2,2-difluoropropane, 2,2-dichloropropane, 2,2-dibromopropane, 2,2-diiodopropane structural formula skeletal formula , abbreviated constitutional formula, displayed formula and skeletal formula

2,2-difluoropropane,  2,2-dichloropropane,  2,2-dibromopropane, 2,2-diiodopropane

Symmetrical molecule, so, reduces the number of NMR chemical shifts resonances.

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 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

Examples of the uses and applications of dihalopropanes i.e. the molecular formulae C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2 and their isomers

These compounds include difluoropropanes, dichloropropanes, dibromopropanes, and diiodopropanes, each with 4–5 isomers depending on chirality.

Overview of the Isomers of the dihalopropanes

Each C3H6X2 compound has:

  • 4 constitutional isomers: e.g. 1,1-, 1,2-, 1,3-, and 2,2-dihalopropanes

  • 1 pair of enantiomers (R/S) for the 1,2-isomer when X ≠ H, giving 5 total isomers per compound

  • Don't make a nomenclature error calling some 2,3-dihalopropanes!

Comparative Summary Table of Isomers and Applications of dihalopropanes

Isomer

Typical Use/Application

Notes

1,1-Dihalopropane

Intermediate in organic synthesis

Less reactive than vicinal isomers

1,2-Dihalopropane - optical (R/S) isomers

Solvent, reagent, or precursor in stereoselective synthesis

Chiral center allows enantiomeric separation

1,3-Dihalopropane

Fumigants, polymer precursor

Use restricted

2,2-Dihalopropane

Volatile solvent, refrigerant (fluoro version), flame retardant (bromo version)

Sterically hindered; affects reactivity

Some uses and applications of difluoropropanes C3H6F2 and their isomers

  • Refrigerants: Especially 1,1-difluoropropane and 2,2-difluoropropane due to low boiling points

  • Blowing agents: Used in foam production

  • Solvents: For specialized organic reactions

  • Pharmaceutical intermediates: Fluorinated compounds often improve bioavailability

Some uses and applications of dichloropropanes C3H6Cl2 and their isomers

  • Industrial solvents: 1,2-dichloropropane used in degreasing and paint stripping

  • Pesticide intermediate: Historically used in soil fumigants (now restricted) e.g. 1,3-dichloropropane

  • Chiral synthesis: R/S isomers of 1,2-dichloropropane used in enantioselective reactions

  • Polymer chemistry: Precursors to chlorinated polymers.

Some uses and applications of dibromopropanes C3H6Br2 and their isomers

  • Flame retardants: Especially 1,2- and 2,2-dibromopropane

  • Alkylating agents: Used in organic synthesis and medicinal chemistry

  • Crosslinkers: 1,3-dibromopropane used in polymer and resin formation

  • Chiral reagents: R/S forms of 1,2-dibromopropane used in stereoselective synthesis

Some uses and applications of diiodopropanes C3H6I2 and their isomers

  • Pharmaceutical intermediates: Iodinated compounds are useful in radiopaque agents and drug design

  • Radioactivelabeling: Iodine isotopes (e.g. I-125, I-131) can be introduced via these isomers

  • Organic synthesis: Excellent leaving group properties make them useful in SN2 reactions

  • Specialty reagents: 1,3-diiodopropane used in macrocycle formation and linker chemistry

Summary Insights for C2H4X2 molecules and their isomers

  • Reactivity increases down the halogen group: F < Cl < Br < I

  • Volatility and environmental impact vary: fluorinated isomers are stable but persistent; iodinated ones are reactive but less volatile

  • Chirality matters: 1,2-isomers offer enantiomeric forms useful in asymmetric synthesis

  • Industrial versus lab use: Fluoro and chloro isomers dominate industrial applications; bromo and iodo are more niche and lab-focused

Learning objectives - questions to be answered?

How do you draw the structural formula and skeletal formula of the isomers of molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

How many aliphatic structural isomers are there of halogen compounds with molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

How many aliphatic carbon chain isomers are there of halogen compounds with molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

How many positional isomers are there of organic halogen molecules with molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

How many E/Z (geometrical) isomers are there of molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

How many R/S (optical) isomers (enantiomers) of molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

Are there any cyclic haloalkene isomers of formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

Are there any cyclo haloalkane isomers of formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

Are there any halodiene isomers of molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

Are there any haloalkyne isomers of molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

Are there any functional group isomers with a molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

Do C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2 organic halogen molecules have any stereoisomers?

Are there any E/Z (geometrical) isomers with a molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

Are there any R/S (optical) isomers (enantiomers) with a molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2?

Be able to deduce the isomers of organic halogen molecules with the formula C3H6Cl2 C3H6Br2 C3H6I2 C3H6F2.

Be able to draw and name the substituted halogen compounds isomers of molecular formula C3H6Cl2 C3H6Br2 C3H6I2 C3H6F2.

Be able to deduce if the isomers of C3H6Cl2 C3H6Br2 C3H6I2 C3H6F2 organic halogen compounds can exhibit R/S optical isomerism.

Be able to deduce if the isomers of C3H6Cl2 C3H6Br2 C3H6I2 C3H6F2 can exhibit E/Z geometrical isomerism (do C3H6Cl2 C3H6Br2 C3H6I2 C3H6F2 have cis/trans geometric isomers).

This page will answer these questions for molecular formula C3H6F2 C3H6Cl2 C3H6Br2 C3H6I2

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

index for all isomerism pages

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of Doc Brown's pre-university advanced level chemistry website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. These organic chemistry revision notes on isomerism are suitable for use of pre-university students studying AQA advanced level chemistry constitutional isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2, Edexcel advanced level chemistry constitutional isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2, OCR advanced level chemistry constitutional isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2, IB advanced level chemistry constitutional isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2, WJEC (Eduqas) advanced level chemistry constitutional isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2, CIE Cambridge advanced level chemistry constitutional isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2, US grade 11-12 AP honors chemistry courses  constitutional isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2 and they will also prove useful to 1st year undergraduate students of chemistry including  constitutional isomers of C3H6F2  , C3H6Cl2  , C3H6Br2  and  C3H6I2.

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