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Doc Brown's
Advanced Chemistry: Part 14.7:
Isomers and extra notes on their properties and uses
The structural isomers of molecular formula C2H6O
[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 C2H6O
[isomerism page updated Feb 9th 2026 *]
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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
The 2
aliphatic
non-cyclic alcohol and ether structural isomers of molecular formula
C2H6O
(Mr = 46)
Percent composition by mass based on atomic masses C = 12.01 H =
1.01 O = 16.00, Mr(C2H6O) = 46.08
Element composition (to two dp): carbon = 52.13%
hydrogen = 13.15% oxygen = 34.72%
Empirical
formula = molecular formula = C2H6O
Introduction and details of the 2 constitutional isomers of C2H6O
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 C 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.
In terms of isomers of
C2H6O
there are
(a) chain variations based on the C and O atoms, which
leads to
(c) functional group isomers of an alcohol and an ether.
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. NOT possible for
C2H6O
Details of the 2 constitutional isomers of
C2H6O
There are only two
constitutional structural isomers of molecular formula C2H6O.
This is an example of functional group
isomerism (alcohol C-O-H linkage, ether C-O-C linkage).
There is one isomeric alcohol
(C-OH
group) and one isomeric
ether (C-O-C link) and no other isomerism is possible for
C2H6O i.e.
no E/Z
or R/S stereoisomerism is possible.
(1) ethanol
(-OH), an
alcohol,
C2H5OH,
CH3CH2OH,
 ,
Abbreviated structural
formulae, displayed formula and skeletal formula, old name ethyl alcohol
Functional group primary
alcohol
C-OH (hydroxyl).
Functional group isomer
(alcohol versus ether).
Number of low resolution
NMR
chemical shift
δ
signal peaks: 3
1H and
2 13C
(email
if disagree?)
1H NMR ratio of peaks: 3 : 2 : 1 (for equivalent protons)
See also
Comparing the infrared spectra of ethanol and
methoxymethane (dimethyl ether)
(2) methoxymethane, an
ether (C-O-C), CH3OCH3,
 ,
(dimethyl ether)
Functional group
ether C-O-C.
Functional group
isomer (alcohol versus ether).
Abbreviated
structural formula, displayed formula and skeletal formula.
Number of low resolution
NMR
chemical shift
δ
signal peaks: 1
1H and
1 13C
See also
Comparing the infrared spectra of ethanol and
methoxymethane (dimethyl ether)
No other forms of isomerism are possible and
this is quite a simple case of functional group isomerism by simply altering the
order of the carbon and oxygen atoms.
Summary of key points and extra notes on the isomers of molecular
formula
C2H6O
The molecular formula C2H6O lends
itself beautifully to exploring several types of isomerism, perfect for
highlighting how even the smallest changes in atomic arrangement can lead to
substantial differences in properties and function.
Comparing the
infrared spectra of ethanol and methoxymethane (dimethyl
ether)
Ethanol and dimethyl ether (methoxymethane) are structural
isomers with the same molecular formula (C2H6O), but
their infrared (IR) spectra differ significantly due to their distinct
functional groups: ethanol is an alcohol, while dimethyl ether is an ether.
Here's a comparative breakdown of their infrared spectra:
Functional Group Differences between ethanol and methoxymethane
|
Feature |
Ethanol
(CH3CH2OH) |
Dimethyl
Ether (CH3OCH3) |
|
Functional
group |
Hydroxyl (-OH) |
Ether (-O-) |
|
Hydrogen
bonding |
Present
(intermolecular) |
Absent |
|
Molecular
polarity |
Higher |
Lower |
Key IR
Absorption Bands for ethanol and methoxymethane
|
Vibrational Mode |
Ethanol
(Alcohol) |
Dimethyl
Ether (Ether) |
|
O–H Stretch |
Broad band at
~3300–3500 cm⁻¹ (strong) |
Absent |
|
C–H Stretch
(alkyl) |
~2850–2970
cm⁻¹ (medium) |
~2850–2970
cm⁻¹ (medium) |
|
C–O Stretch |
~1050–1150
cm⁻¹ (strong) |
~1000–1100
cm⁻¹ (strong) |
|
O–H Bend |
~1400–1440
cm⁻¹ (medium) |
Absent |
|
CH₃
Rocking/Bending |
~1350–1470
cm⁻¹ |
~1350–1470
cm⁻¹ |
|
Fingerprint
Region |
Complex, with
broad O–H contributions |
Simpler,
sharper ether bands |
Sources:
NIST WebBook for Dimethyl Ether,
Infrared Intensities of Alcohols and Ethers – Rogers, 1980
Interpretation Highlights of the infrared spectra ethanol and methoxymethane
-
Ethanol’s broad O–H stretch is a hallmark
of hydrogen bonding and is absent in dimethyl ether.
-
Dimethyl ether’s spectrum lacks the broad
hydrogen-bonding features and shows sharper C–O stretches due to its
symmetrical ether structure.
-
The C–O stretching region overlaps in both
but differs in intensity and exact position due to the bonding environment.
Types
of Isomerism for molecular formula C2H6O
|
Isomer Type |
Isomers |
Structural
Difference |
Description |
|
Functional group
constitutional
(structural) functional group isomers |
Ethanol versus Dimethyl
ether |
Alcohol (C-OH) versus
Ether (C-O-C) |
Different functional
groups entirely |
|
Same as above |
Connectivity of atoms
differs |
All functional group
isomers are structural isomers |
|
Stereoisomerism |
Not applicable here |
No chiral centres or
double bonds |
Stereoisomerism requires
additional complexity |
Differences in Physical Properties
of the isomers of molecular formula
C2H6O
|
Property |
Ethanol
(CH3CH2OH) |
Methoxymethane
(dimethyl ether)
(CH3OCH3) |
Reason |
|
Boiling point |
78 °C |
-24 °C |
London + polar + hydrogen bonding versus
weaker Van der Waals forces only |
|
Solubility in
water |
Very soluble |
Moderately soluble |
Ethanol forms hydrogen
bonds with water |
|
State at room temp |
Liquid |
Gas |
Due to differences in intermolecular
bonding forces |
|
Smell |
Characteristic alcoholic
scent |
Ether-like, slightly sweet |
Functional group dependent |
Differences in Chemical Properties
of the isomers of molecular formula
C2H6O
|
Reaction Type |
Ethanol |
Methoxymethane (dimethyl
ether) |
|
Combustion |
Combusts to
CO2 + H2O |
Same general
combustion |
|
Oxidation |
Oxidizes to
ethanal → ethanoic acid |
Not readily
oxidized under same conditions |
|
Reaction with Na |
Produces H2
(typical of alcohols) |
No reaction |
|
Acid/base behaviour |
Weak acid (can
donate H⁺ from OH) |
No protic
hydrogen; behaves neutral |
|
Reaction with carboxylic
acids |
Forms ethyl esters with acid
catalyst |
No reaction |
Uses
and Applications
of the isomers of molecular formula
C2H6O
|
Compound |
Uses |
|
Ethanol |
Antiseptic,
solvent, fuel, alcoholic beverages, intermediate in organic
synthesis |
|
Dimethyl ether |
Propellant in
aerosols, refrigerant, potential clean fuel alternative |
Common
Misconceptions
about the isomers of molecular formula
C2H6O
-
“Same formula means same properties”:
Molecular formula alone doesn't dictate behavior—structure is everything!
-
“Only one kind of isomerism possible”:
Students often overlook conformational isomerism and think only functional
group isomerism matters.
-
“Both are alcohols”: Dimethyl ether is not
an alcohol despite having an oxygen; it lacks the hydroxyl (-OH) group.
Exam
Tips for questions involving
the isomers of molecular formula
C2H6O
-
Always draw structures when asked about isomerism—words
alone might lose marks.
-
Clearly differentiate between structural and functional
group isomerism; they often overlap but are assessed separately.
-
Link differences in boiling point and solubility to
intermolecular forces (Hydrogen bonding versus Dipole-induced dipole).
-
Quote examples of reactions (e.g., ethanol + sodium) to
demonstrate chemical differences.
-
Check if the question hints at "physical and
chemical properties”—both must be addressed!
Learning objectives - questions to be answered?
How do you work out the structure
of the isomers of molecular formula C2H6O?
How do you draw the structural
formula and skeletal formula of the isomers of molecular formula
C2H6O?
How do you name the isomers of molecular formula
C2H6O?
How many aliphatic structural
isomers are there of molecular formula C2H6O?
How many aliphatic carbon chain
isomers are there of molecular formula C2H6O?
How many positional isomers are
there of molecular formula C2H6O?
How many E/Z (geometrical) isomers
are there of molecular formula C2H6O?
How many R/S (optical) isomers
(enantiomers) of molecular formula C2H6O?
Are there any functional group
isomers with a molecular formula C2H6O?
Does C2H6O have any stereoisomers?
Are there any E/Z (geometrical)
isomers with a molecular formula C2H6O?
Are there any R/S (optical) isomers
(enantiomers) with a molecular formula C2H6O?
This page will answer these questions for molecular formula C2H6O
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
M olecular structure and naming of aliphatic ALCOHOLS including isomeric ethers
Examples of effects of isomerism on similarity or difference in the
physical & chemical properties of structural isomers
Comparison of the ir,
mass, 1H and 13C NMR spectra of the isomers of C2H6O
(via a 1H NMR
spectrum page)
INDEX of ALL revision notes on the chemistry of ALCOHOLS (and mention of ethers)
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
Keywords or phrases: how many isomers are
there of molecular formula C2H6O? how do you name the isomers of
molecular formula C2H6O? what is the molecular structure of the
isomers of C2H6O, what type of isomerism is exhibited by molecules
of formula C2H6O, how do you work out the isomers of molecular
formula C2H6O, what are the structural isomers of C2H6O, the carbon chain
isomers of C2H6O in the homologous series of alkanes, comparing
the spectra of isomers of molecular formula C2H6O how many structural isomers of
C2H6O can you draw? how many structural isomers does C2H6O have?
what are the possible isomers of C2H6O? revision notes on
isomerism of C2H6O molecules, isomerism in
aliphatic alcohols, isomerism in aliphatic ethers, alcohol
isomers of C2H6O, ether isomers of C2H6O the molecular structure
of the isomers of C2H6O,
isomers of C2H6O of molecular mass 46 ethers alcohols molecules
isomeric with molecular formula C2H6O, structural isomers of
molecular formula C2H6O, optical isomers R/S enantiomers
isomeric with molecular formula C2H6O, positional isomers
isomeric with molecular formula C2H6O, which types of isomerism
are exhibited by molecules isomeric with molecular formula C2H6O
alkyl positional isomers of C2H6O branched carbon chain ethers
alcohols isomers of C2H6O
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isomerism are
suitable for use of pre-university students studying AQA advanced level
chemistry constitutional isomers of C2H6O, Edexcel advanced level
chemistry constitutional isomers of C2H6O, OCR advanced level
chemistry constitutional isomers of C2H6O, IB advanced level
chemistry constitutional isomers of C2H6O, WJEC (Eduqas) advanced
level chemistry constitutional isomers of C2H6O, CIE Cambridge advanced level chemistry
constitutional isomers of C2H6O, US grade 11-12 AP honors
chemistry courses constitutional isomers of C2H6O and they will also prove useful to
1st year undergraduate students of chemistry including
constitutional isomers of C2H6O. |
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