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Doc Brown's
Advanced Chemistry: Part 14.7
Isomers and extra notes on their properties and uses
Structural
constitutional isomers of molecular formula C3H5F , C3H5Cl
, C3H5Br
and
C3H5I
[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 C3H5X
[isomerism page updated Feb 11th 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 4 constitutional structural
isomers of molecular formula
C3H5F , C3H5Cl , C3H5Br
and
C3H5I
Relative molecular mass and
percent composition by mass
based on the 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 |
|
C3H5F |
60.08 |
59.97 |
8.41 |
31.62 |
|
C3H5Cl |
76.53 |
47.08 |
6.60 |
46.32 |
|
C3H5Br |
120.98 |
29.78 |
4.18 |
66.04 |
|
C3H5I |
167.98 |
21.45 |
3.01 |
75.54 |
Empirical formula
=
molecular formula =
C3H5X
Introduction to isomerism in molecules of formulae
C3H5F
, C3H5Cl , C3H5Br
and C3H5I
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.
(a) The carbon chain can be linear (aliphatic) or
cyclic (alicyclic).
(b) Positional isomers due the different substituent
positions of the halogen atom.
(c) Unsaturated open chain alkenes versus
cycloalkane isomers.
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.
One of
the halogenated alkenes can display 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.
Not possible here.
Note
Some of the
C3H5F, C3H5Cl, C3H5Br
and C3H5I 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!).
The images of
C3H5X (X =
F, Cl, Br and I)
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.
They are all open chain
unsaturated alkene (aliphatic) or a cycloalkane (alicyclic) compounds derived from halogen mono-substitution products of
hydrocarbons with the formula C3H6 (propene and
cyclopropane).
The are 4
constitutional-structural isomers of molecular formula
C3H5X (X =
F, Cl, Br and I),
irrespective of any E/Z or R/S isomerism that may be possible.
Since one of the structural isomers exhibits E/Z isomerism there
is a total of 5 distinct isomers for C3H5X.
Non of the isomers exhibits R/S isomerism, no carbon atom acts
as an asymmetric chiral carbon atom centre.
Since one isomer exhibits E/Z isomerism, there a total of 5
distinct isomers for the molecular formula C3H5X.
Details of the four
constitutional structural isomers
C3H5F , C3H5Cl , C3H5Br
and
C3H5I
Total of 5 isomers if you include both E/Z stereoisomers.
(1)
CH3-CH=CHX,
,
1-halopropenes
Functional group isomer (open chain alkene versus cycloalkane) and
positional isomer (position of halogen -X).
The structural formula and skeletal formula representing:
1-fluoropropene,
1-chloropropene, 1-bromopropene and 1-iodopropene.
Old names e.g. propenyl chloride
Other IUPAC names:
1-fluoroprop-1-ene, 1-chloroprop-1-ene,
1-bromoprop-1-ene, 1-iodoprop-1-ene
1-fluoro-1-propene, 1-chloro-1-propene,
1-bromo-1-propene, 1-iodo-1-propene
They exhibit E/Z (geometrical) isomerism, with E
(trans) and Z (cis) isomers (images above).
From the CIP priority rule:
ZX > 6C > 1H
about the C=C bond, X = halogen, and Z = 9, 17, 35 or 53
They would be named
e.g. (E)-1-chloropropene or
(E)-1-chloroprop-1-ene
e.g. (Z)-1-chloropropene or
(Z)-1-chloroprop-1-ene etc.
Number of low resolution
NMR chemical
shift
δ
signal peaks: 3 1H
and 3 13C
(email
if disagree?)
1H NMR ratio of peaks: 3 : 1 : 1 (for equivalent protons)
Index of
1H NMR spectra
organic compounds and
Index of
13C NMR
spectra organic compounds
(2) 2-halopropenes,
CH3-CX=CH2,
 ,
structural formula and skeletal formula
Functional group isomer (open chain alkene versus cycloalkane) and
positional isomer (position of halogen -X).
The structural formula and skeletal formula representing:
2-fluoropropene,
2-chloropropene, 2-bromopropene and 2-iodopropene.
Other names:
2-fluoroprop-1-ene, 2-chloroprop-1-ene,
2-bromoprop-1-ene, 2-iodoprop-1-ene
2-fluoro-1-propene, 2-chloro-1-propene,
2-bromo-1-propene, 2-iodo-1-propene
Number of low resolution
NMR chemical
shift
δ
signal peaks: 2 1H
and 3 13C
(email
if disagree?)
1H NMR ratio of peaks: 3 : 2 (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.
(3)
3-halopropenes,
XH2C-CH=CH2,
 ,
structural formula, skeletal formula
Functional group isomer (open chain alkene versus cycloalkane) and
positional isomer (position of halogen -X).
The structural formula and skeletal formula representing:
3-fluoropropene,
3-chloropropene, 3-bromopropene and 3-iodopropene.
Old names e.g. allyl chloride
Other names:
3-fluoroprop-1-ene, 3-chloroprop-1-ene,
3-bromoprop-1-ene, 3-iodoprop-1-ene
3-fluoro-1-propene, 3-chloro-1-propene,
3-bromo-1-propene, 3-iodo-1-propene
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 : 2 (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.
(4)
, skeletal formula, no E/Z or R/S stereoisomerism possible
Functional group isomer (open chain alkene versus cycloalkane).
The skeletal formula representing: fluorocyclopropane,
chlorocyclopropane, bromocyclopropane and iodocyclopropane.
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) : 1 (for equivalent protons)
Summary of key points and extra exam revision notes on the isomers of molecular
formulae
C3H5F , C3H5Cl , C3H5Br
and
C3H5I
and their properties and uses
Isomers of C3H5X
(where X = F, Cl, Br, or I), a useful family for examining isomerism,
reactivity, and trends across the halogen group. Some 'halogen' trends
described are not attributable to isomerism
Overview: Molecular Formula
C3H5X
-
These molecules contain 3 carbon atoms,
5 hydrogen atoms, and 1 halogen.
-
Limited atoms means relatively few constitutional
isomers—but multiple types of isomerism appear.
Types
of Isomerism exhibited by isomers of
C3H5F , C3H5Cl , C3H5Br
and
C3H5I
|
Isomerism Type |
Description |
Examples
(Generalised) |
|
Structural
(Constitutional) -
Positional Isomerism |
Connectivity differs,
halogen X on different carbon positions. |
e.g. 1-chloropropene
versus 2-chloropropene;
X at C1 versus C2 versus C3 positions. |
|
Geometric (E/Z or
cis/trans) |
Restricted rotation around
C=C due to X and H positions. |
e.g. 1-chloropropene shows
E/Z due to asymmetry. |
| Functional group isomerism |
linear alkene versus cyclic alkane |
1-chloropropene versus
chlorocyclopropane |
Physical Properties trends of
C3H5F , C3H5Cl , C3H5Br
and
C3H5I
|
Property |
Trend/Comparison |
|
Boiling
Point |
Increases with
halogen atomic mass: F < Cl < Br < I |
|
Polarity |
C–F most polar →
strongest dipole–dipole interactions |
|
Solubility
(in water) |
Higher for
fluorides due to polarity; decreases with size of halogen. |
|
Density |
Heavier halogens
increase density (I > Br > Cl > F) |
Reactivity and Chemical Reactions exhibited by isomers of
C3H5F , C3H5Cl , C3H5Br
and
C3H5I
|
Isomer |
Typical
Reactions |
Reactivity
Notes |
|
Allyl halide (CH2=CHCH2X) |
Readily undergo SN1, SN2,
allylic nucleophilic substitution and electrophilic additions |
The 3-halo-1-propenes,
different positional isomers can have different reactivities |
|
Vinyl halide (CH3CH=CHX) |
Generally less
reactive to nucleophilic substitution and electrophilic
addition |
The 1-halo-1-propenes |
|
1-halo-2-propene
isomers |
Can undergo elimination →
form alkynes or dienes |
Reactivity varies with
halogen: I > Br > Cl > F |
Uses
and Applications of by isomers of
C3H5F , C3H5Cl , C3H5Br
and
C3H5I
|
Isomer
Type |
Application |
|
Allyl
halides |
Synthesis of
polymers, drugs, perfumes; versatile intermediates |
|
Vinyl
halides |
Precursors to
vinyl polymers like PVC (vinyl chloride) |
|
Halopropenes |
Used in
agrochemicals, flame retardants, and specialty polymers |
Common
Misconceptions about by isomers of
C3H5F , C3H5Cl , C3H5Br
and
C3H5I
(see also below)
-
Vinyl halides easily undergo substitution —
Not true; their C–X bond is strong and resistant.
-
Halogen defines reactivity more than structure
— Structure (allylic versus vinylic) often dictates the reaction pathway
more than which halogen is present.
-
All isomers are similarly reactive — Allyl
halides are often far more reactive than positional or vinyl counterparts.
Exam
Revision Tips for questions involving isomers of
C3H5F, C3H5Cl, C3H5Br
and
C3H5I
(see also above)
-
Learn to identify functional groups and positions
-
Remember boiling point trends across
halogens: heavier halogens raise it.
-
Practice drawing E/Z and positional isomers—structure helps
clarify properties and mechanisms.
-
Use the halogen series to predict trends:
C–F strongest bond, C–I weakest and most reactive.
Learning objectives - questions to be answered?
How do you draw the structural formula
and skeletal formula of the isomers of molecular formula C3H5F C3H5Cl
C3H5Br C3H5I?
How many aliphatic structural isomers
are there of molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
How many aliphatic carbon chain isomers
are there of molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
How many positional isomers are there
of molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
How many E/Z (geometrical) isomers are
there of molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
How many R/S (optical) isomers
(enantiomers) of molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
Are there any cycloalkene isomers of
formula C3H5F C3H5Cl C3H5Br C3H5I?
Are there any cyclic haloalkene isomers
of formula C3H5F C3H5Cl C3H5Br C3H5I?
Are there any cyclo haloalkane isomers
of formula C3H5F C3H5Cl C3H5Br C3H5I?
Are there any diene isomers of
molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
Are there any alkyne isomers of
molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
Are there any functional group isomers
with a molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
Do C3H5F C3H5Cl C3H5Br
C3H5I have any stereoisomers?
Are there any E/Z (geometrical) isomers
with a molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
Are there any R/S (optical) isomers
(enantiomers) with a molecular formula C3H5F C3H5Cl C3H5Br C3H5I?
Be able to deduce the isomers of
organic halogen molecules with the formula C3H5Cl C3H5Br C3H5I
C3H5F.
Be able to draw and name the
substituted halogen compounds
isomers of molecular formula C3H5Cl C3H5Br C3H5I C3H5F.
Be able to deduce if
the isomers of C3H5Cl C3H5Br C3H5I C3H5F organic halogen compounds can exhibit R/S optical isomerism.
Be able to deduce if the isomers of
C3H5Cl C3H5Br C3H5I C3H5F can exhibit E/Z geometrical isomerism (do
C3H5Cl C3H5Br C3H5I C3H5F have cis/trans geometric
isomers).
This page
will answer these questions for molecular formula
C3H5F
C3H5Cl C3H5Br
and C3H5I
Associated organic chemistry links
Advanced Level pre-university
organic chemistry notes
IR, mass and H-1 and C-13
NMR spectra of organic compounds
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 polymersFor 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
|
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 C3H5F , C3H5Cl , C3H5Br and
C3H5I, Edexcel advanced level
chemistry constitutional isomers of C3H5F , C3H5Cl , C3H5Br and
C3H5I, OCR advanced level
chemistry constitutional isomers of C3H5F , C3H5Cl , C3H5Br and
C3H5I, IB advanced level chemistry
constitutional isomers of C3H5F , C3H5Cl , C3H5Br and C3H5I, WJEC (Eduqas) advanced level
chemistry constitutional isomers of C3H5F , C3H5Cl , C3H5Br and
C3H5I, CIE Cambridge advanced level chemistry
constitutional isomers of C3H5F , C3H5Cl , C3H5Br and C3H5I, US grade 11-12 AP honors
chemistry courses constitutional isomers of C3H5F , C3H5Cl ,
C3H5Br and C3H5I and they will also prove useful to
1st year undergraduate students of chemistry including
constitutional isomers of C3H5F , C3H5Cl , C3H5Br and C3H5I. |
Keywords
or phrases: how many isomers are there of molecular formula
C3H5F C3H5Cl C3H5Br C3H5I?
how do you name the isomers of molecular formula C3H5F C3H5Cl
C3H5Br C3H5I? what is
the molecular structure of the isomers of C3H5F C3H5Cl C3H5Br
C3H5I, what type of
isomerism is exhibited by molecules of formula C3H5F C3H5Cl
C3H5Br C3H5I, how do you
work out the isomers of formula C3H5F C3H5Cl C3H5Br C3H5I, what are the
structural isomers of C3H5F C3H5Cl C3H5Br C3H5I, the carbon chain isomers of
C3H5F C3H5Cl C3H5Br C3H5I in
the homologous series of alkanes, comparing the many structural
isomers does C3H5F C3H5Cl C3H5Br C3H5I have? what are the possible isomers of
C3H5F C3H5Cl C3H5Br C3H5I?
revision notes on isomerism of C3H5F C3H5Cl C3H5Br C3H5I molecules, the molecular
structure of the isomers of C3H5F C3H5Cl C3H5Br C3H5I how to draw the structural
formula of isomers of C3H5F C3H5Cl C3H5Br C3H5I, how to draw the displayed formula of
isomers of C3H5F C3H5Cl C3H5Br C3H5I, how to draw the skeletal formula of isomers of
C3H5F C3H5Cl C3H5Br C3H5I, how to name the isomers of molecular formula
C3H5F C3H5Cl C3H5Br C3H5I,
R/S optical isomers enantiomers of C3H5F C3H5Cl C3H5Br C3H5I
isomeric with molecular formula C3H5F C3H5Cl C3H5Br C3H5I, structural isomers of
molecular formula C3H5F C3H5Cl C3H5Br C3H5I, optical isomers R/S enantiomers isomeric
with molecular formula C3H5F C3H5Cl C3H5Br C3H5I, positional isomers isomeric with
cycloalkenes and alkynes of molecular formula C3H5F C3H5Cl
C3H5Br C3H5I, which types
of isomerism are exhibited by molecules of formula C3H5F C3H5Cl
C3H5Br C3H5I alkyl
positional isomers of C3H5F C3H5Cl C3H5Br C3H5I branched carbon chain isomers of
C3H5F C3H5Cl C3H5Br C3H5I
cycloalkanes of molecular formula C3H5F C3H5Cl C3H5Br C3H5I which are isomeric with
alkenes of molecular formula C3H5F C3H5Cl C3H5Br C3H5I stereoisomers of molecular
formula C3H5F C3H5Cl C3H5Br C3H5I,
optical isomers R/S enantiomers isomeric with molecular formula
C3H5F C3H5Cl C3H5Br C3H5I, positional isomers isomeric with molecular formula
C3H5F C3H5Cl C3H5Br C3H5I,
which types of isomerism are exhibited by C3H5F C3H5Cl C3H5Br
C3H5I alkyl positional
isomers of C3H5F C3H5Cl C3H5Br C3H5I, how to work out the
isomers of C3H5F C3H5Cl C3H5Br C3H5I
How to deduce the isomers of
organic halogen molecules with the formula C3H5Cl C3H5Br C3H5I
C3H5F, How to write, draw and name the substituted halogen
compounds isomers of molecular formula C3H5Cl C3H5Br C3H5I
C3H5F, How to deduce if the isomers of C3H5Cl C3H5Br C3H5I C3H5F
organic halogen compounds can exhibit R/S optical isomerism, How to deduce if the isomers of
C3H5Cl C3H5Br C3H5I C3H5F can exhibit E/Z geometrical isomerism (do
C3H5Cl C3H5Br C3H5I C3H5F have cis/trans geometric
isomers?), number of structural isomers of C3H5Cl C3H5Br C3H5I
C3H5F, number of stereoisomers of C3H5Cl C3H5Br C3H5I C3H5F
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