isomers of C3H7F, C3H7Cl, C3H7Br and C3H7I

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Advanced level chemistry PART 14.7: Structural isomers of molecular formula C3H7F C3H7Cl C3H7Br C3H7I

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

Structural isomers of molecular formula C3H7F, C3H7Cl, C3H7Br and C3H7I

[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 and US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectroscopy and analysing the isomers of C3H7X [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? *  [privacy policy] 

The two structural isomers of molecular formula  C3H7F , C3H7Cl , C3H7Br and C3H7I

Relative molecular mass and percent composition 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
C3H7F 62.10 58.02 11.38 30.60
C3H7Cl 78.55 45.87 9.00 45.13
C3H7Br 123.00 29.29 5.75 64.96
C3H7I 170.00 21.19 4.16 74.65

Empirical formula = molecular formula = C3H7X

Introduction to isomerism in molecules of formulae  C3H7F C3H7Cl C3H7Br and C3H7I

If applicable (but not here, 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.

Just (b) for the position of the halogen atom, and that's it.

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.

Neither applicable here.

Note

Some of the C3H7F C3H7Cl C3H7Br and C3H7I 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, but all of these 4 x 2 isomers all exist.

For images of the isomers of C3H7X, X = F, Cl, Br and I halogens from group 7/17 of the periodic table.

There are no isomers possible for CH3X or C2H5X, you need a minimum of three carbon atoms.

The are only 2 constitutional-structural isomers per molecular formula C3H7X (X = F, Cl, Br and I), and no E/Z or R/S isomerism is possible, so, nice and simple - just two positional isomers based on the position of the halogen atom.

This means there are only 2 distinct isomers for per molecular formula C3H7X (X = F, Cl, Br and I)

They are all halogen substitution products of the hydrocarbon alkane propane C3H8 and are examples of the group of organic compounds known as haloalkanes or halogenoalkanes.

Details of the constitutional structural isomers C3H7F C3H7Cl C3H7Br and C3H7I

names of the 2 constitutional isomers of formula C3H7F, C3H7Cl, C3H7Br or C3H7I molecular formula skeletal formula constitutional structural formula

(1) CH3CH2CH2X, abbreviated structural formula, skeletal formula of 1-fluoropropane, 1-chloropropane, 1-bromopropane and 1-iodopropane haloalkane isomers , skeletal formula

1-fluoropropane, 1-chloropropane, 1-bromopropane and 1-iodopropane

These are primary haloalkanes.

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 : 2  (for equivalent protons)

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

A specific example of abbreviated structural formula, displayed formula and skeletal formula.

for 1-bromopropane, CH3CH2CH2Br, displayed structural formula of 1-bromopropane isomer of molecular formula C3H7Br , skeletal formula of 1-bromopropane isomer of molecular formula C3H7Br, primary haloalkane,

 

(2) CH3CHXCH3, abbreviated structural formula , skeletal formula of 2-fluoropropane, 2-chloropropane, 2-bromopropane and 2-iodopropane haloalkane isomers , skeletal formula

2-fluoropropane, 2-chloropropane, 2-bromopropane and 2-iodopropane

These are secondary haloalkanes.

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

1H NMR ratio of peaks: 6  (3+3) : 1  (for equivalent protons)

A specific example of abbreviated structural formula, displayed formula and skeletal formula.

for 2-bromopropane, CH3CHBrCH3,  displayed structural formula of 2-bromopropane isomer of molecular formula C3H7Br , skeletal formula of 2-bromopropane isomer of molecular formula C3H7Br, secondary haloalkane, 

(c) doc b is a 3D representation of 2-bromopropane for a 2D screen or paper!

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

The infrared spectrum of 1-bromopropane

The infrared spectrum of 2-bromopropane

The infrared spectrum of 1-chloropropane

The infrared spectrum of 2-chloropropane

The infrared spectrum of 1-iodopropane

The infrared spectrum of 2-iodopropane

The mass spectrum of 1-bromopropane

The mass spectrum of 2-bromopropane

The mass spectrum of 1-chloropropane

The mass spectrum of 2-chloropropane

The mass spectrum of 1-iodopropane

The mass spectrum of 2-iodopropane

The H-1 NMR spectrum of 1-bromopropane

The H-1 NMR spectrum of 2-bromopropane

The H-1 NMR spectrum of 1-chloropropane

The H-1 NMR spectrum of 2-chloropropane

The H-1 NMR spectrum of 1-iodopropane

The H-1 NMR spectrum of 2-iodopropane

The C-13 NMR spectrum of 1-bromopropane

The C-13 NMR spectrum of 2-bromopropane

The C-13 NMR spectrum of 1-chloropropane

The C-13 NMR spectrum of 2-chloropropane

The C-13 NMR spectrum of 1-iodopropane

The C-13 NMR spectrum of 2-iodopropane

Examples of the uses and applications of halopropanes i.e. the molecular formulae C3H7F  , C3H7Cl  , C3H7Br  and  C3H7I and their isomers

A comprehensive breakdown of the uses and applications of the isomers of the halogenated propane derivatives with molecular formula C3H3X (X = F, Cl, Br, I). Each has two positional isomers: 1-halo- and 2-halo-propane.

A Structural Isomers Overview

Formula

Isomers

Structures

C3H7F

1-fluoropropane, 2-fluoropropane

CH3CH2CH2F and CH3CH(F)CH3

C3H7Cl

1-chloropropane, 2-chloropropane

CH3CH2CH2Cl and CH3CH(Cl)CH3

C3H7Br

1-bromopropane, 2-bromopropane

CH3CH2CH2Br and CH3CH(Br)CH3

C3H7I

1-iodopropane, 2-iodopropane

CH3CH2CH2I and CH3CH(I)CH3

Each pair differs by the position of the halogen atom, which affects reactivity, boiling point, and synthetic utility.

Comparative Table of Uses of halopropanes

Compound

Isomer

Applications

C3H7F

1-fluoropropane

Refrigerant, low-GWP propellant, intermediate in fluorinated drug synthesis

 

2-fluoropropane

Similar uses; slightly different boiling point and reactivity

C3H7Cl

1-chloropropane

Solvent, alkylating agent, intermediate in agrochemicals

 

2-chloropropane

Used in SN1/SN2 reaction studies, polymer precursor

C3H7Br

1-bromopropane

Industrial solvent (degreasing), flame retardant precursor, alkylation reagent

 

2-bromopropane

More reactive in SN1 reactions, used in stereoselective synthesis

C3H7I

1-iodopropane

Excellent leaving group in organic synthesis, radiolabeling precursor

 

2-iodopropane

Used in SN1/SN2 comparisons, pharmaceutical intermediate

Key Insights

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

  • Leaving group ability improves from fluoride to iodide, making C₃H₇I isomers highly useful in substitution reactions

  • 1-halo isomers tend to be more linear and less sterically hindered, favouring SN2 reactions

  • 2-halo isomers are more branched, often favouring SN1 mechanisms and showing different boiling points

Synthetic and Educational Uses

  • Mechanistic studies: These isomers are textbook examples for comparing SN1 versus SN2 pathways

  • Spectroscopy standards: Useful in IR and NMR training due to distinct chemical shifts

  • Pharmaceutical precursors: Especially iodopropanes and fluoropropanes in radiolabeling and drug design

  • Environmental relevance: Fluoropropanes are studied for their low global warming potential as refrigerants

Comparison of the physical properties of  the molecular formulae C3H7F  , C3H7Cl  , C3H7Br  and  C3H7I and their isomer compounds

Selected examples of the Physical Properties of C3H7X Compounds where X can be F, Cl, Br or I

Compound

Isomer Type

Boiling Point (oC)

Melting Point (oC)

Density (g/cm³)

Refractive Index

Water Solubility

Notes

C3H7F

1-Fluoropropane

−2.5

−159

0.782

1.323

2.4 g/dm3

Highly volatile
C3H7F 2-fluoropropane -10 -133 0.969 1.328 3.1 g/dm3 Highly volatile

C3H7Cl

1-Chloropropane

46

−123

0.892

1.388

2.7 g/dm3

Clear, flammable
C3H7Cl 2-chloropropane 35 -118 0.859 1.395 3.1 g/dm3  
C3H7Br 1-bromopropane 71 -110 1.35 1.434 2.5 g/dm3  

C3H7Br

2-Bromopropane

60

−89

1.31

1.425

3.2 g/dm3

Used in synthesis

C3H7I

1-Iodopropane

101

−101

1.74

1.504

1.1 g/dm3

Light-sensitive
C3H7I 2-iodopropane 90 -90 1.70 1.498 1.4 g/dm3  

Isomer Comparison

Each compound has two isomers:

  • 1-halo-propane: Halogen on the terminal carbon (primary halide, haloalkane)

  • 2-halo-propane: Halogen on the middle carbon (secondary halide, haloalkane)

Key Differences:

  • Boiling Points: 1-isomers generally have slightly higher boiling points due to stronger dipole moments, all the compounds increase with increase in atomic number of the halogen - increase in intermolecular forces with increase in number of electrons per molecule.

  • Reactivity: 2-isomers (secondary halides) are more reactive in SN1 reactions due to carbocation stability.

  • Density & Refractive Index: Increase with heavier halogens (F < Cl < Br < I).

  • Water Solubility: Tends to decrease with increasing halogen size due to reduced polarity and increased hydrophobicity, but not a very strong trend?

Learning objectives - questions to be answered?

How do you draw the structural formula and skeletal formula of the isomers of molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

How many aliphatic structural isomers are there of halogen compounds with molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

How many aliphatic carbon chain isomers are there of halogen compounds with molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

How many positional isomers are there of organic halogen molecules with molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

How many E/Z (geometrical) isomers are there of molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

How many R/S (optical) isomers (enantiomers) of molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

Are there any halocycloalkene isomers of formula C3H7F C3H7Cl C3H7Br C3H7I?

Are there any cyclic haloalkene isomers of formula C3H7F C3H7Cl C3H7Br C3H7I?

Are there any cyclo haloalkane isomers of formula C3H7F C3H7Cl C3H7Br C3H7I?

Are there any halodiene isomers of molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

Are there any haloalkyne isomers of molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

Are there any functional group isomers with a molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

Do C3H7F C3H7Cl C3H7Br C3H7I organic halogen molecules have any stereoisomers?

Are there any E/Z (geometrical) isomers with a molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

Are there any R/S (optical) isomers (enantiomers) with a molecular formula C3H7F C3H7Cl C3H7Br C3H7I?

Be able to deduce the isomers of organic halogen molecules with the formula C3H7Cl C3H7Br C3H7I C3H7F.

Be able to draw and name the substituted halogen compounds isomers of molecular formula C3H7Cl C3H7Br C3H7I C3H7F.

Be able to deduce if the isomers of C3H7Cl C3H7Br C3H7I C3H7F organic halogen compounds can exhibit R/S optical isomerism.

Be able to deduce if the isomers of C3H7Cl C3H7Br C3H7I C3H7F can exhibit E/Z geometrical isomerism (do C3H7Cl C3H7Br C3H7I C3H7F have cis/trans geometric isomers).

This page will answer these questions for molecular formula C3H7F C3H7Cl C3H7Br C3H7I

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

Index of revision notes on the chemistry of ALKANES and the petrochemical industry

Index of revision notes on the chemistry ALKENES including reactions and polymers

 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

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