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Doc Brown's
Advanced Chemistry: Part 14.7
Selected
constitutional structural
functional group isomers of molecular formula
C5H10O2
[Author
©
Dr
WP Brown 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 C5H10O2
[spectra page updated Feb 23rd 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
Sub-index for this
page on the isomers of
C5H10O2
Introduction to isomerism for
molecular formula
C5H10O2
(a)
4 carboxylic acid isomers of formula
C5H10O2
(b)
9 ester isomers of
formula C5H10O2
(c)
Selected methoxy or hydroxy-aldehydes and
methoxy or hydroxy-ketones of formula C5H10O2
(d)
Selected ene-diols
with molecular formula
C5H10O2
(e)
Selected alicyclic isomers of
formula C5H10O2
(f)
Selected heterocyclic isomers of
formula C5H10O2
(g) A few
extra comments on the spectra of selected isomers of
C5H10O2
Introduction to the
isomerism, selected constitutional isomers and stereoisomers of molecular formula C5H10O2
Composition of
C5H10O2
Percent composition based on atomic masses C= 12.01 H =
1.01 O = 16.00 and Mr(C5H10O2)
= 102.15
Element composition (to two dp): carbon = 58.79%
hydrogen = 9.89% oxygen = 31.33%
Empirical formula = molecular formula =
C5H10O2
Please
note there are a very large number of isomers of molecular formula C5H10O2
and this page presents a selection of them and where appropriate
indicates the type of isomerism involved.
Structural isomerism
- isomers of the same specific molecular formula, based on different connectivity's of the constituent atoms
(the constitutional isomers), so
they cannot be spatially identical (but sometimes 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 e.g.
In terms of isomers of
C5H10O2
there are
(a) chain variations based on the C or O atoms, open chain aliphatic linear, branched and cyclic (alicyclic)
and heterocyclic structures,
(b) positional isomers e.g. hydroxy group in
the aldehydes and ketones, substituent positions in the cyclic
compounds.
(c) They are all functional group isomers of
each other
e.g. in terms e.g. carboxylic acids, esters, hydroxy-aldehydes, hydroxy-ketones,
alkene-alcohols (unsaturated 'enols'), saturated substituted cycloalkane
based molecules.
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)
This is where
molecules have the same basic constitutional structural formula, but
isomers differ in the 2D/3D arrangement of the atoms.
For stereoisomers, the (CIP) abbreviation
means the
IUPAC Cahn-Ingold-Prelog priority order rule for assigning
E/Z (geometrical) and R/S (optical)
stereoisomers.
E/Z stereoisomerism
was called 'geometrical isomerism' e.g.
cis (= Z) and
trans (= E) isomers of alkenes
or disubstituted cyclic alkanes where there are 2D/3D spatial variations
that are not mirror images and not super imposable.
There are
many examples of E/Z geometrical isomers
in open chain compounds via the C=C restricted rotation or two
substituents in a ring where both can be above the 'plane' of a ring or one above and one below the plane of the ring
- can be complicated with overlapping R/S optical isomerism for the
same molecule as in the case 1,2-dimethylpropane.
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 (enantiomers).
The molecule must have a chiral centre
(a stereocentre), that is an asymmetric carbon atom with four different
atoms/groups attached to it.
There many examples of R/S optical isomers,
but, as already mentioned, it can be complicated with overlapping E/Z
geometric isomers for the same molecule and some molecules,
particularly the 'cyclic' ring containing molecules may have two or
three chiral centres (asymmetric carbon atoms).
NOTE
Initially I have chosen examples of isomers
that pre-university students are most likely to come across, and that is usually
carboxylic acids and esters.
There are huge number of constitutional isomers (I've
identified at least ~50, theoretical or actual) and many stereoisomers (at
least~29 pairs) of formula C5H10O2 and
there are many more.
NEXT (a-e) Details of selected constitutional isomers
and stereoisomers of
C5H10O2
below.
(a)
and (b) Examples of aliphatic
carboxylic acid and ester structural isomers of molecular formula
C5H10O2
(a) There are four constitutional isomeric carboxylic acids (1) to (4)
of molecular formula
C5H10O2
Note that COOH is shorthand for the
4 carboxylic acid's functional group
O=C-O-H
(1)
pentanoic acid ,
 ,
 ,
Number of low resolution
NMR
chemical shift
δ
signal peaks:
5
1H and
5
13C
(email
if disagree?)
1H NMR ratio of peaks: 3 : 2 : 2
: 2 : 1 (for equivalent protons)
(2)
2-methylbutanoic acid ,
CH3CH2CH(CH3)COOH,
 ,
This molecule has a chiral carbon (the C of
the CH group), so this molecule will exhibit R/S
stereoisomerism, optical isomers - non-superimposable
mirror image forms known as enantiomers.
Number of low resolution
NMR
chemical shift
δ
signal peaks:
5
1H and
5
13C
(email
if disagree?)
1H NMR ratio of peaks: 3 : 2 : 1
: 3 : 1 (for equivalent protons)
(3)
3-methylbutanoic acid ,
(CH3)2CHCH2COOH,
 ,
Number of low resolution
NMR
chemical shift
δ
signal peaks:
4
1H and
4
13C
(email
if disagree?)
1H NMR ratio of peaks: 6
(3+3) : 1 : 1 (for equivalent protons)
(4)
2,2-dimethylpropanoic acid ,
(CH3)3CCOOH
,
,
Number of low resolution
NMR
chemical shift
δ
signal peaks:
2
1H and
3
13C
(email
if disagree?)
1H NMR ratio of peaks: 9
(3x3) : 1 (for equivalent protons)
(b) There are nine
constitutional isomeric esters e.g (5) to (13)
of molecular formula
C5H10O2
Note that COOC shorthand for the ester
linkage functional group
O=C-O-C
The 9
esters illustrated below.
(5)
methyl butanoate
(methyl butyrate),
 ,
An ester made
from butanoic acid and methanol.
(6)
ethyl propanoate,
 ,
An ester made
from propanoic acid and ethanol.
(7)
propyl ethanoate ,
,
An ester made
from ethanoic acid and propan-1-ol.
Brief
notes on the IR, mass, 1H NMR & 13C NMR spectrums of
propyl ethanoate
(8) butyl methanoate,
HCOOCH2CH2CH2CH3 ,
,
An ester made
from methanoic acid and butan-1-ol.
(9) 1-methylethyl ethanoate, CH3COOCH(CH3)2 ,
,
An ester made
from ethanoic acid and propan-2-ol. (isopropyl acetate)
(10) methyl 2-methylpropanoate,
(CH3)2CHCOOCH3 ,
,
An ester made
from 2-methylpropanoic acid and methanol.
(11) 1-methypropyl methanoate,
HCOOCH(CH3)CH2CH3 ,
 ,
An ester made from methanoic acid and butan-2-ol, R/S
isomers
(12) 2-methylpropyl methanoate,
HCOOCH2CH(CH3)2 ,
 ,
An ester made from methanoic acid and 2-methylpropan-1-ol
(13) 1,1-dimethylethyl methanoate,
HCOOC(CH3)3 ,
 ,
An ester made from methanoic acid and 2-methylpropan-2-ol
For
examples (c) onwards, you are more likely to come across them at university
level, but the odd structure may crop up in advanced pre-university chemistry
courses.
(c)
There are also lots
of methoxy- or hydroxy-aldehydes and methoxy- or
hydroxy-ketones with a C5H10O2
molecular formula
For the functional groups
in abbreviated structural formulae, note ...
CO is the >C=O carbonyl group of ketones (named
...one),
and CHO is the
H-C=O aldehyde group (named ...al),
plus some have an ether
C-O-C group linkages (instead of an OH hydroxy group) e.g.
via the methoxy group OCH3
A molecule with a chiral carbon (often the C of a CH group), will exhibit R/S
stereoisomerism, exhibiting R/S isomers, optical isomers -
non-superimposable mirror image forms known as enantiomers.
Note that IUPAC nomenclature rules state that the aldehyde
or ketone group takes precedence over the ether methoxy or hydroxy alcohol groups, the
compounds are named with the ...al or ...one suffix and the
alcohol named as the hydroxy substituent prefix. Take care with the prefix
number too!
Some of the hydroxy-aldehyde
or methoxy-aldehyde
isomers of molecular formula
C5H10O2
Isomers with a linear carbon chain
with an aldehyde and alcohol functional groups
CH3CH2CH2CH(OH)CHO
2-hydroxypentanal, R/S isomers, C2 chiral
CH3CH2CH(OH)CH2CHO
3-hydroxypentanal, R/S isomers
C3 chiral
CH3CH(OH)CH2CH2CHO
4-hydroxypentanal, R/S isomers
C4 chiral
HOCH2CH2CH2CH2CHO
5-hydroxypentanal
and two
methoxy-aldehydes (ether-aldehydes)
CH3OCH2CH2CH2CHO
4-methoxybutanal
CH3CH(OCH3)CH2CHO
3-methoxybutanal, R/S isomers
C3 chiral
Isomers with a branched carbon chain
(CH3)2CHCH(OH)CHO
2-hydroxy-3-methylbutanal, R/S isomers
C2 chiral
(CH3)2C(OH)CH2CHO
3-hydroxy-3-methylbutanal
HOCH2CH(CH3)CH2CHO
4-hydroxy-3-methylbutanal, R/S isomers
C3 chiral
Some of the hydroxy-ketone
or methoxy-ketone isomers of molecular formula C5H10O2
Isomers with a linear carbon chain
with a ketone and alcohol functional group
CH3CH2CH2COCH2OH
1-hydroxypentan-2-one (1-hydroxy-2-pentanone)
CH3CH2CH(OH)COCH3
3-hydroxypentan-2-one (3-hydroxy-2-pentanone), R/S isomers,
C3 chiral
CH3CH(OH)CH2COCH3
4-hydroxypentan-2-one (4-hydroxy-2-pentanone), R/S isomers,
C4 chiral
HOCH2CH2CH2COCH3
5-hydroxypentan-2-one (5-hydroxy-2-pentanone)
HOCH2CH2COCH2CH3
1-hydroxypentan-3-one (1-hydroxy-3-pentanone)
CH3CH(OH)COCH2CH3
2-hydroxypentan-3-one (2-hydroxy-3-pentanone), R/S isomers,
C3 chiral
and two methoxy-ketones
(ether-ketones)
CH3OCH2COCH2CH3
1-methoxybutan-2-one (1-methoxy-2-buttanone)
CH3CH(OCH3)COCH3
3-methoxybutan-2-one (3-methoxy-2-butanone), R/S isomers,
C4 chiral
Isomers with a branched carbon chain
HOCH2COCH(CH3)2
1-hydroxy-3-methylbutan-2-one
CH3COC(OH)(CH3)2
3-hydroxy-3-methylbutan-2-one
CH3COCH(CH3)CH2OH
4-hydroxy-3-methylbutan-2-one, R/S isomers,
C3 chiral
(d)
Selected examples of ene-diols
with molecular formula
C5H10O2
e.g. some examples based on pentenes
with an alkene group and two alcohol (diol) functional groups
CH2=CHCH(OH)CH(OH)CH3
pent-4-ene-2,3-diol, R/S isomers,
C3 chiral, NOT E/Z isomerism
CH2=CHCH2CH(OH)CH2OH
pent-4-ene-2,3-diol, R/S isomers,
C2 chiral, NOT E/Z isomerism
CH3CH=CHCH(OH)CH2OH
pent-3-ene-2,3-diol R/S isomers (C2 chiral) and E/Z isomerism, complex
overlapping stereoisomerism)
The
first two are based on pent-1-ene, but named on the IUPAC higher priority
'ol' group.
The
third is based on pent-2-ene, but again, named on the IUPAC higher
priority 'ol' group.
So, there are lots more ene-diols based on pentenes and
methylbutenes.
You can also have lots of alkoxy enols i.e. molecules with
an alkene, alcohol and ether linkage functional groups e.g
CH2=CHCH(OCH3)CH2OH,
2-methoxypent-3-ene-1-ol, R/S isomers, because C2 is chiral.
(e)-(f) There are also
many cyclic compounds
of molecular formula
C5H10O2
(e)
Selected examples of alicyclic
compounds of
C5H10O2
Saturated
cyclic compounds with a ring of 3, 4 or 5 carbon atoms
e.g.
cyclopentane diols
and
cyclopentane-1,2-diol and
cyclopentane-1,3-diol and these two diols exhibit
E/Z geometrical (cis/trans) overlapping with R/S optical isomerism,
2 chiral centres, so a complicated stereoisomerism situation!
Five more are illustrated
below involving cyclopentane, cyclobutane and cyclopropane rings.
(1) There is also theoretically
cyclopentane-1,1-diol, which does NOT exhibit either E/Z or
R/S isomerism. (Note there is no cyclic 1,4 diol until cyclohexane diols)
(2)
3-methylcyclobutane-1,2-diol, two secondary alcohol
groups, can exhibit complex
'overlapping' E/Z and R/S isomerism, 3 chiral centres, C1, C2
and C3.
(3)
2-methoxycyclobutan-1-ol,
secondary alcohol and ether functional groups, can exhibit complex 'overlapping' E/Z and R/S isomerism,
two
chiral centres, C1 and C2.
(4)
3,3-dimethylcyclopropane-1,2-diol,
two secondary alcohol
groups, can exhibit complex
'overlapping' E/Z and R/S isomerism, two
chiral centres, C1 and C2.
(5)
2-ethoxycyclopropan-1-ol,
secondary alcohol and ether functional groups, can exhibit complex 'overlapping' E/Z and R/S isomerism, 2
chiral centres, C1 and C2.
There are dozens
of other possibilities where the substituent alkyl, hydroxyl
(alcohol) or alkoxy (ether) groups can go.
(f)
Selected examples of alicyclic compounds
S aturated
cyclic compounds, which, theoretically, can have a ring of 3 to 7
carbon or oxygen atoms.
Six examples are
illustrated below involving six different heterocyclic ring systems
(not named).
(1) Based on a 1,4-epoxybutane ring and secondary
alcohol group
complex
'overlap' of E/Z and R/S isomerism, two
chiral centres (C3 and C4).
(2) Based on a 1,2-dioxolane ring,
complex
'overlap' of E/Z and R/S isomerism, two
chiral centres (C2 and C3).
(3)
Based on a 1,3-dioxolane ring,
complex 'overlap' of E/Z and R/S
isomerism, two
chiral centres (C2 and C4).
(4) Based on an oxetane ring and secondary alcohol
group,
complex
'overlap' of E/Z and R/S isomerism, two
chiral centres (C2 and C3).
(5) Based on a 1,3-dioxetane ring,
complex
'overlap' of E/Z and R/S isomerism, two
chiral centres (C2 and C4).
(6) Based on a 1,2-epoxy ring and a primary alcohol
group,
complex
'overlap' of E/Z and R/S isomerism, two
chiral centres (C1 and C2 of the ring).
Like the alicyclic
examples above, there are dozens of other possibilities where the
substituent alkyl, hydroxyl (alcohol) or alkoxy (ether) groups can
go and .even more possibilities involving carbon and oxygen ring
systems.
Over 100 isomers of C5H10O2
isomers commercially available via
https://www.molport.com/shop/molecular-formula/C5H10O2
(g)
A few extra spectra comments of selected isomers of
C5H10O2
Constitutional isomers of
C5H10O2
show distinct infrared (IR) spectra due to differences in functional groups
and molecular connectivity. Key spectral differences arise from the presence
of carboxylic acid, ester aldehydes, ketone, alcohol and ether groups.
Overview:
C5H10O2
Constitutional Isomers
This molecular formula allows for several isomers including:
Each has different functional group environments, which affect
their IR spectra.
Key IR Spectral Features by Isomer Type of formula
C5H10O2
| Example in isomer |
Key IR Peaks (cm⁻¹) |
| hydroxyl group C-O-H |
Broad O–H stretch ~3200–3600; C–O
~1050–1150 |
Student Exam Tips for Spectral
Interpretation
-
Broad O–H peaks suggest hydrogen bonding
(diols).
-
Sharp C–O–C peaks indicate ether linkages.
-
Presence of carbonyl peaks suggests
aldehydes, ketones or carboxylic acids.
-
Presence of C=C suggests unsaturation e.g. alkene
Learning objectives - questions to be answered?
How do you work out the structure
of the isomers of molecular formula C5H10O2?
How do you draw the structural
formula and skeletal formula of the isomers of molecular formula
C5H10O2?
How do you name the isomers of molecular formula
C5H10O2?
How many aliphatic structural
isomers are there of molecular formula C5H10O2?
How many aliphatic carbon chain
isomers are there of molecular formula C5H10O2?
How many positional isomers are
there of molecular formula C5H10O2?
Are there any
aliphatic open chain alkene isomers of molecular formula C5H10O2?
Are there any carboxylic acid isomers of
molecular formula C5H10O2?
Are there any ester
isomers of molecular formula C5H10O2?
Are there any
alkene-alcohol enol isomers of molecular formula C5H10O2?
Are there any alkene isomers of molecular formula
C5H10O2?
Are there any alcohol isomers of molecular formula
C5H10O2?
Are there any aldehyde isomers of molecular formula
C5H10O2?
Are there any ketone isomers of molecular formula
C5H10O2?
Are there any functional group
isomers with a molecular formula C5H10O2?
Does C5H10O2 have any stereoisomers?
Are there any E/Z (geometrical)
isomers with a molecular formula C5H10O2?
Are there any R/S (optical) isomers
(enantiomers) with a molecular formula C5H10O2?
How many E/Z (geometrical) isomers
are there of molecular formula C5H10O2?
How many R/S (optical) isomers
(enantiomers) of molecular formula C5H10O2?
This page will answer these questions
for molecular formula C5H10O2
Associated organic chemistry links
Advanced Level pre-university
organic chemistry notes
IR, mass and H-1 & C-13 NMR
spectra of organic compounds
Examples of the effects of isomerism on the similarity or difference
in the physical and chemical properties of structural isomers
Index of sets of isomers for a given
molecular formula
The molecular structure and naming of CARBOXYLIC ACIDS and DERIVATIVES,
including isomers
INDEX of ALL revision notes on the
chemistry of CARBOXYLIC ACIDS and DERIVATIVES 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
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The isomerism of molecular formula C5H10O2.
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C5H10O2
R/S optical isomers enantiomers of C5H12O2,
isomers of C5H10O2 of molecular mass 102 carboxylic acid molecules isomeric of molecular formula C5H10O2, ester molecules isomeric with molecular formula C5H10O2, ketones hydroxyketones isomeric with molecular formula C5H10O2, aldehydes hydroxyaldehydes isomeric with molecular formula C5H10O2, alkenediols isomeric with molecular formula C5H10O2, structural isomers of molecular formula C5H10O2, optical isomers R/S enantiomers isomeric with molecular formula C5H10O2, positional isomers isomeric with molecular formula C5H10O2, which types of isomerism are exhibited by molecules isomeric with molecular formula C5H10O2
Diagrams of the structure
of the isomers of C5H10O2,
Drawings the structural
formula and skeletal formula of the isomers of C5H10O2, names of the isomers of
C5H10O2, structural isomers are of C5H10O2, the number of carboxylic acid isomers of
C5H10O2, number of ester
isomers of C5H10O2, the alkene-alcohol enol isomers of C5H10O2, the alkene isomers of
C5H10O2, alcohol isomers of C5H10O2? the aldehyde isomers of
C5H10O2, the ketone isomers of C5H10O2, the any functional group
isomers with a C5H10O2 the
stereoisomers of C5H10O2,
the E/Z geometrical isomers of C5H10O2, the R/S optical
isomers (enantiomers) of C5H10O2
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