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Doc Brown's
Advanced Chemistry: Part 14.7
The two constitutional
structural chain isomers of molecular formula C4H10
[Author
©
Dr
Phil Brown GRIC, PhD:
Doc Brown's advanced level organic chemistry exam revision notes
suitable for students of UK advanced level chemistry courses, IB advanced
chemistry & US K12 grades
11-12 and AP honors chemistry courses: Molecular
spectroscopy and analysing the isomers of C4H10
[page updated
RE-EDIT]
Sub-index for this page on the isomers of C4H10
(1)
Introduction to the isomerism of molecular formula C4H10
(2)
Details of the isomers of C4H10
(3)
Extra information about the isomers of C4H10
(4)
Learning objectives related to the isomers of C4H10
(5)
Practise exam questions
based on the isomers of C4H10
(with ANSWERS)
Associated organic chemistry page links
Index of sets of isomers for a given
molecular formula
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brown - comments - query?
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(1) Introduction
The two
alkane carbon chain structural isomers
of molecular formula C4H10
(Mr = 58)
details below
Introduction
to isomerism for molecular formula
C4H 10
(see also summary
diagram)
Percent composition of
C4H10 based on atomic masses C= 12.01 H =
1.01 and Mr(C4H10) = 58.14
Element composition (to two dp): carbon = 82.63%
hydrogen = 17.37%
Empirical formula = C2H5 and
molecular formula = C4H10
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 (a) chain branching is applicable here.
Stereoisomerism - isomers
based on the same connectivity of the atoms (same constitutional formula), but
in some way, they are 2D or 3D spatially different non-superimposable images (e.g. E/Z
'geometrical' isomers or mirror image R/S 'optical' isomers)
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.
Not applicable 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.
Not applicable here.
Note
These are open
chain saturated aliphatic compounds called alkanes.
In terms of the carbon chain,
butane would be described as 'linear' and methylpropane as 'branched'.
This is the first instant of the existence of structural
isomers, (carbon chain isomers), for an alkane molecular formula with different
carbon chain arrangements (chain isomerism), this is NOT possible with methane, ethane or
propane.
No E/Z or R/S isomers possible, no
stereoisomerism.
Molecular formula
C4H10
is the first in the homologous alkane series
CnH2n+2
to exhibit isomerism in any form.
Note that methane CH4, ethane C2H6
and propane C3H8 cannot display any types of isomerism.
There are no E/Z or R/S stereoisomers
and no functional group isomerism possible either.
There are 2
constitutional
structural isomers of molecular formula C4H10,
with no E/Z and R/S isomers, because there
are just two possible carbon chain
isomers for this aliphatic open chain alkane formula
(2) Isomer details
for molecular formula C4H10
(1)
 or
 are abbreviated structural formulae for
butane
The skeletal formula is
,
the full displayed formula (ignoring
bond angles!) is
Number of low resolution
NMR
chemical shift
δ
signal peaks: 2
1H and
2 13C
(email
if disagree?)
1H NMR integrated ratio of peaks: 6
(3+3) : 4 (2+2) (for equivalent protons)
See also spectra that can distinguish one C4H10
isomer from another
The
infrared spectrum of butane
The
infrared spectrum of 2-methylpropane
The
mass spectrum of butane
The mass
spectrum of 2-methylpropane
The H-1 NMR spectrum of butane
The H-1
NMR spectrum of 2-methylpropane
The C-13 NMR spectrum of butane
The
C-13 NMR spectrum of 2-methylpropane
Index of 1H NMR spectra organic
compounds and
Index of 13C NMR spectra organic
compounds
(2)
 or
 are the abbreviated structural formula for
2-methylpropane
and the skeletal formula is
Number of low resolution
NMR
chemical shift
δ
signal peaks: 2
1H and
2 13C
(email
if disagree?)
1H NMR integrated ratio of peaks: 9
(3x3) : 1
(for equivalent protons)
See also spectra links above.
(3) Summary and extra
information on the isomers of C4H10
Molecular Formula: C4H10
Number of Constitutional
Isomers: 2
|
Isomer Name |
Structure Type |
Condensed Formula |
|
n-Butane |
Straight-chain alkane |
CH₃–CH₂–CH₂–CH₃ |
|
2-methylpropane
(isobutane) |
Branched alkane |
(CH₃)₃CH |
These differ in carbon connectivity, making
them constitutional (structural) isomers.
Types of Isomerism
Exhibited
|
Type of Isomerism |
Explanation |
|
Constitutional
Isomerism |
Different connectivity
of atoms (straight versus branched chain) |
|
No
Stereoisomerism |
No chiral centres or
restricted rotation in C₄H₁₀ |
Differences in Physical
Properties
|
Property |
n-Butane |
Isobutane
(2-methylpropane) |
|
Boiling Point |
~ –0.5 °C |
~ –11.7 °C |
|
Melting Point |
~ –138 °C |
~ –159.6 °C |
|
Density (g/cm³) |
Slightly higher |
Slightly lower |
|
Volatility |
Lower |
Higher |
Explanation: Branched isomers have weaker
London dispersion forces due to compact shape → lower boiling points.
Differences in Chemical
Reactions
Both are saturated alkanes, so they undergo:
-
Combustion: Complete → CO2 + H2O;
Incomplete → CO + C + H2O
-
Free Radical Substitution: With halogens
(Cl2, Br2) under UV light
Reactivity
Differences
-
Methylpropane (isobutane) has tertiary
hydrogen → more reactive in radical
halogenation (e.g., forms tert-butyl halides).
-
n-Butane gives mixtures of primary and
secondary halides.
Uses and Applications
|
Isomer |
Uses and
Applications |
|
n-Butane |
LPG fuel, aerosol
propellant, feedstock in petrochemicals |
|
Isobutane |
Refrigerant (R-600a),
alkylation feedstock in gasoline |
Common Student
Misconceptions
-
Thinking C4H10 has more than 2
isomers — confusing conformers with constitutional isomers.
-
Assuming branched alkanes are always more reactive
— depends on reaction type.
-
Forgetting that physical properties are
influenced by intermolecular forces, not just molecular
weight.
Exam Revision Tips
(AQA, Edexcel, OCR,
WJEC, CCEA, CIE, IB, AP)
-
Draw both isomers and label primary,
secondary, tertiary carbons.
-
Practice free radical substitution
mechanisms with both isomers.
-
Compare boiling points and explain using
molecular shape and dispersion forces.
-
Use reaction maps: alkane → halogenoalkane
→ alcohol → alkene.
-
Mnemonic: “Branched = Boils Below” →
Isobutane has lower boiling point.
(4)
Learning objectives - questions to be answered?
Can you IUPAC name these isomers
of molecular formula
C4H10?
Can you deduce the number of principal 1H chemical
shifts and proton ratio you would expect to see in the NMR spectrum of
these
C4H10
isomers?
Can you deduce the number of principal 13C chemical
shifts you would expect to see in the NMR spectrum of these
C4H10
isomers?
How do you work out the isomers of
molecular formula C4H10?
How do you draw the structural
formula and skeletal formula of the isomers of molecular formula
C4H10?
How many aliphatic structural
isomers are there of molecular formula C4H10?
How many aliphatic carbon chain
isomers are there of molecular formula C4H10?
How many positional isomers are
there of molecular formula C4H10?
How many E/Z (geometrical) isomers
are there of molecular formula C4H10?
How many R/S (optical) isomers
(enantiomers) of molecular formula C4H10?
Are there any aliphatic open chain
alkene isomers of molecular formula C4H10?
Are there any diene isomers of
molecular formula C4H10?
Are there any alkyne isomers of
molecular formula C4H10?
Are there any alicyclic cycloalkane
isomers of molecular formula C4H10?
Are there any alicyclic cycloalkene
isomers of molecular formula C4H10?
Are there any functional group
isomers with a molecular formula C4H10?
Does C4H10 have any stereoisomers?
Are there any E/Z (geometrical)
isomers with a molecular formula C4H10?
Are there any R/S (optical) isomers
(enantiomers) with a molecular formula C4H10?
This
page will answer these questions for molecular formula C4H10.
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(5) QUESTIONS
Practise exam questions
based on isomers of molecular formula
the isomers of C4H10
Jot
down your responses
with explanations!
ANSWERS
to the questions based on the
isomers of
C4H10
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
How many isomers have a molecular formula of
C4H10? and can you name them and
draw their skeletal formula?
Q2 Do all the isomers of
C4H10 have relatively low
boiling points?
Q3
Can some of the structural isomers of
C4H10 exhibit R/S optical
stereoisomerism
Q4
Is the empirical formula for all isomers of
C4H10 also the molecular
formula C4H10 ?
Q5 Will the more branched isomer of
C4H10 have a lower boiling
point?
Q6
On reaction with chlorine/uv will one C4H10
isomer give one mono-chloroalkane and the other isomer
gives two mono-chlorinated alkanes?
Q7
Are all the isomers of
C4H10 are saturated
alkanes?
Q8
Is the interconversion reaction of
C4H10 isomers called a
tautomerism reaction?
Q9
Is it true that one isomer will only give one principal
1H NMR signal and one 13C NMR signal and the other
isomer will two principal 1H and two 13C NMR signals?
Check out the proton ratios!
ANSWERS
to the questions based on the
isomers of
C4H10
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.
|
Associated organic chemistry links
Advanced Level pre-university
organic chemistry notes
IR, mass and H-1 & C-13 NMR
spectra of organic compounds
Index of sets of isomers for a given
molecular formula
[ SEARCH
BOX]
This is a BIG
website, you need to take time to explore it.
The molecular structure and
naming of ALKANES
Comparison of the ir,
mass, 1H and 13C NMR spectra of the isomers of C4H10
(via a 1H NMR spectrum page)
Index of revision notes
on the chemistry of ALKANES and the petrochemical
industry
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
Summary diagram of isomerism which
links to details of the types of isomerism
Keywords or phrases: how many isomers are
there of molecular formula C4H10? how do you name the isomers of
molecular formula C4H10? what is the molecular structure of the
isomers of C4H10, what type of isomerism is exhibited by molecules
of formula C4H10, how do you work out the isomers of molecular
formula C4H10, what are the structural isomers of C4H10, the carbon chain
isomers of C4H10 in the homologous series of alkanes, comparing
the spectra of isomers of molecular formula C4H10 how many
structural isomers of C4H10 can you draw? how many structural
isomers does C4H10 have? what are the possible isomers of C4H10?
revision notes on isomerism of C4H10 molecules,
isomers of C4H10 of molecular mass 58 alkane molecules isomeric of molecular formula C4H10, ester molecules isomeric with molecular formula C4H10, structural isomers of molecular formula C4H10, optical isomers R/S enantiomers isomeric with molecular formula C4H10, positional isomers isomeric with molecular formula C4H10, which types of isomerism are exhibited by molecules isomeric with molecular formula C4H10 alkyl positional isomers of C4H10 branched carbon chain alkane isomers of C4H10
alkane molecules isomeric of molecular formula
C4H10,
ester molecules isomeric with molecular formula C4H10, structural isomers of molecular
formula C4H10, optical isomers R/S enantiomers isomeric with molecular
formula C4H10, positional isomers isomeric with molecular formula
C4H10,
which types of isomerism are exhibited by molecules isomeric with
molecular formula C4H10 alkyl positional isomers of C4H10 branched
carbon chain alkane isomers of C4H10
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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 the isomers of C4H10
with names, structures, types of isomerism and a few spectroscopy details 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, CCEA advanced level chemistry, US grade 11-12 AP honors
chemistry courses and they will also prove useful to
1st year undergraduate students of chemistry. |
|
ANSWERS
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
Q1
How many isomers have a molecular formula of
C4H10? and can you name them and
draw their skeletal formula?
ANSWER
(1)
,
butane,
(2)
,
2-methylpropane
Q2 Do all the isomers of
C4H10 have relatively low
boiling points?
ANSWER
Yes, they are all small non-polar molecules
with weak intermolecular bonding forces, hence
relatively low kinetic particle energies needed to
overcome them and vapourise.
Q3
Can some of the structural isomers of
C4H10 exhibit R/S optical
stereoisomerism
ANSWER
Not possible, no
C4H10 isomer has a chiral
carbon.
Q4
Is the empirical formula for all isomers of
C4H10 also the molecular
formula C4H10 ?
ANSWER
Incorrect
C4H10/2 =
C2H5
Q5 Will the more branched isomer of
C4H10 have a lower boiling
point?
ANSWER
Yes,
more branching, more compact, lesser surface area, less
polarizable molecule, weaker intermolecular bonding
forces, hence relatively low kinetic needed to overcome
them and vapourise.
Q6
On reaction with chlorine/uv will one C4H10
isomer give one mono-chloroalkane and the other isomer
gives two mono-chlorinated alkanes?
ANSWER
Incorrect, both yield two possible products
butane yields 1-chlorobutane and
2-chlorobutane
2-methypropane yields 1-chloro-2-methylpropane
and 2-chloro-2-methylpropane
Q7
Are all the isomers of
C4H10 are saturated
alkanes?
ANSWER
True,
C4H10 complies with the
general alkane formula CnH2n+2, so
saturated with no C=C bond
Q8
Is the interconversion reaction of
C4H10 isomers called a
tautomerism reaction?
ANSWER
Incorrect,
the reaction is called isomerisation.
Q9
Is it true that one isomer will only give one principal
1H NMR signal and one 13C NMR signal and the other
isomer will two principal 1H and two 13C NMR signals?
Check out the proton ratios!
ANSWER
Not true:
Both isomers give two 1H and two 13C NMR signals, each
has two different proton and carbon atom chemical
environment.
C H3CH2CH2CH3
(proton ratio 6:4) and (CH3)3CH
(proton ratio 9:1)
If you think there are
any errors, please email me asap at
chem55555@hotmail.com
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