|
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
Phil Brown GRIC, 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
RE-EDIT]
Sub-index
for this page on the isomers of
C3H7X
(X = halogen)
(a)
Introduction to the constitutional-structural
isomers of formula C3H7X
(b)
Details of
the constitutional isomers of molecules of formulae
C3H7X
(c)
Extra notes
on the constitutional isomers of molecules of C3H7X
(X = halogen)
(d)
Learning objectives - questions to be answered?
(e)
Practise exam questions
based on isomers of
C3H7X
(X = halogen)
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]
(a) Introduction to isomerism in molecules of formulae
C3H7F
C3H7Cl C3H7Br
and
C3H7I
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
Isomerism applicable
(see also 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.
(b) Details of the
constitutional structural isomers
C3H7F C3H7Cl
C3H7Br
and
C3H7I
(1) CH3CH2CH2X,
abbreviated structural formula,
, 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,
,
 , primary haloalkane,
(2) CH3CHXCH3,
abbreviated structural formula ,
, 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,
 ,
 ,
secondary haloalkane,
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
(c)
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?
(d)
Learning objectives - questions to be answered?
Can you IUPAC name these isomers
of molecular formula C3H7F, C3H7Cl, C3H7Br and C3H7I?
Can you deduce the number of principal 1H chemical
shifts and proton ratio you would expect to see in the NMR spectrum of
these
C3H7F, C3H7Cl, C3H7Br and C3H7I?
isomers?
Can you deduce the number of principal 13C chemical
shifts you would expect to see in the NMR spectrum of these
C3H7F, C3H7Cl, C3H7Br and C3H7I?
isomers?
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
(e) QUESTIONS
| Practise exam questions
based on isomers of molecular formula
C3H7X,
X = F, Cl, Br and I
Jot
down your responses
with explanations!
ANSWERS
to the questions based on the isomers of
C3H7X,
X = F, Cl, Br and I
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
I don't mind if students/teachers do a selected printout
of these questions and answers.
Q1
Derive the structural formula and skeletal formula and names of
the isomers of molecular C3H7Br and
classify them in terms of their functional group.
Q2 Based
on the number of expected principal chemical shifts in the
1H and 13C NMR of the isomers of C3H7Br,
how far could you distinguish between these isomers?
Think 'chemical environments' and the integrated proton
signal ratio.
Q3 (a)
Which isomer will react the fastest when refluxed with aqueous
sodium hydroxide and why?
(b) Write an equation for the reaction, name the product and
state the type of reaction mechanism involved.
Q4
Do any of the isomers of C3H7Br exhibit
E/Z (geometrical) or R/S (optical)
stereoisomerism?
ANSWERS to the questions based on the isomers of
C3H7X,
X = F, Cl, Br and I
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
|
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
Index of my advanced
(pre-college/university) organic
chemistry revision notes
Index
of all my spectroscopy pages
Index
of all my isomerism pages
The chemistry of
alkanes and the petrochemical
industry
The
chemistry of alkenes
The
chemistry of haloalkanes
The
chemistry of
alcohols
The chemistry of
aldehydes
and ketones The
chemistry of carboxylic acids and derivatives The chemistry of
organo-nitrogen compounds
The chemistry of
aromatic compounds
A summary chart of isomerism
| 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. |
Keywords or phrases: how many isomers are
there of halogen compounds of molecular formula C3H7F C3H7Cl
C3H7Br C3H7I? what is the
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what are the possible isomers of C3H7F C3H7Cl C3H7Br C3H7I? revision notes on
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C3H7F C3H7Cl C3H7Br C3H7I,
R/S optical isomers enantiomers of C3H7F C3H7Cl C3H7Br C3H7I isomeric with molecular formula
C3H7F C3H7Cl C3H7Br C3H7I, structural isomers of molecular
formula C3H7F C3H7Cl C3H7Br C3H7I, optical isomers R/S enantiomers isomeric with molecular
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haloalkanes, haloalkynes, haloalkenes of molecular formula C3H7F
C3H7Cl C3H7Br C3H7I,
which types of isomerism are exhibited by molecules of formula
C3H7F C3H7Cl C3H7Br C3H7I alkyl positional isomers of C3H7F
C3H7Cl C3H7Br C3H7I branched carbon chain
isomers of C3H7F C3H7Cl C3H7Br C3H7I,
stereoisomers of molecular formula C3H7F C3H7Cl C3H7Br C3H7I,
optical isomers R/S enantiomers isomeric with molecular
formula C3H7F C3H7Cl C3H7Br C3H7I, positional isomers isomeric with molecular formula
C3H7F C3H7Cl C3H7Br C3H7I,
which types of isomerism are exhibited by C3H7F C3H7Cl C3H7Br C3H7I halogen atom positional isomers of
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organic halogen molecules with the formula C3H7Cl C3H7Br C3H7I
C3H7F, How to write, draw and name the substituted halogen
compounds isomers of molecular formula C3H7Cl C3H7Br C3H7I
C3H7F, How to deduce if the isomers of C3H7Cl C3H7Br C3H7I C3H7F
organic halogen compounds can exhibit R/S optical isomerism, How 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?), number of structural isomers of C3H7Cl C3H7Br C3H7I
C3H7F, number of stereoisomers of C3H7Cl C3H7Br C3H7I C3H7F
|
ANSWERS
Practise exam questions
based on isomers of molecular formula
C3H7X,
X = F, Cl, Br and I
Jot
down your responses
with explanations!
ANSWERS
to the questions based on the isomers of
C3H7X,
X = F, Cl, Br and I
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
I don't mind if students/teachers do a selected printout
of these questions and answers.
Q1
Derive the structural formula and skeletal formula and names of
the isomers of molecular C3H7Br and
classify them in terms of their functional group.
ANSWERS
(1) 1-bromopropane,
CH3CH2CH2Br,
, primary haloalkane,
(2) 2-bromopropane,
CH3CHBrCH3 ,
,
secondary haloalkane,
(1) and (2) are structural
positional isomers of C3H7Br
Q2 Based
on the number of expected principal chemical shifts in the
1H and 13C NMR of the isomers of C3H7Br,
how far could you distinguish between these isomers?
Think 'chemical environments' and the integrated proton
signal ratio.
ANSWERS
(1) CH3CH2CH2Br,
will give three 1H and three 13C NMR
chemical shifts, proton ratio 3:2:2.
(2)
CH3CHBrCH3,
will give two 1H and two 13C NMR
chemical shifts, proton ratio 6:1.
Therefore they can be clearly distinguished by
their NMR spectra, the symmetry of 2-bromopropane reduces the
maximum possible number of NMR chemical shifts and a simpler
proton ratio.
Q3 (a)
Which isomer will react the fastest when refluxed with aqueous
sodium hydroxide and why?
(b) Write an equation for the reaction, name the product and
state the type of reaction mechanism involved.
ANSWERS
(a)
Secondary haloalkanes react faster than primary haloalkanes (for the
same halogen), so 2-bromopropane will react faster than
1-bromopropane because a secondary carbocation is more stable than a
primary one.
(b)
CH3CHBrCH3,
+ OH- ===>
CH3CHOHCH3 + Br-
The product is propan-2-ol via a nucleophilic
substitution mechanism.
Q4
Do any of the isomers of C3H7Br exhibit
E/Z (geometrical) or R/S (optical)
stereoisomerism?
ANSWERS
NO,
there is no C=C bond and no chiral (asymmetric) carbon atom.
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
|
|
