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Doc Brown's
Advanced Chemistry: Part 14.7:
Isomers
and extra notes on their properties and uses
Selected
constitutional structural
isomers, carbon chain, positional, functional group and stereoisomers of molecular formula
C4H8O2
[Author
©
Dr
Phil Brown PhD:
Doc Brown's advanced level organic chemistry exam revision notes
suitable for students of UK advanced level chemistry courses & US K12 grade
11, grade 12 and AP honors chemistry courses: Molecular
spectroscopy and analysing the isomers of C4H8O2
[page updated
RE-EDIT]
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
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and disclaimer]
Sub-index for
this page on the many isomers of molecular formula C4H8O2
(a) to (k)
are open chain aliphatic compounds
(a)
Introduction to this page on the isomers of C4H8O2
(development, chemical composition and important links)
(b)
Introduction to the
isomerism and selected isomers of molecular formula C4H8O2
(c)
There are 2 carboxylic acids
of molecular formula C4H8O2
(molecules 1-2)
(d)
There
are
4 esters
of molecular formula
C4H8O2
(molecules 4-6)
(e-g)
Lots
of hydroxy-aldehydes, hydroxy-ketones & carbonyl-ethers C4H8O2
(e)
5 hydroxy-aldehyde
isomers of C4H8O2
(molecules 7-11)
(f)
3 hydroxy-ketone isomers of C4H8O2
(molecules 12-14)
(g)
4 Ether-carbonyl compounds, methoxy-aldehydes/ketones and
an ethoxy aldehyde (molecules 33-36)
(h)
18 Ene-diols
(18 unsaturated diols)
with molecular formula
C4H8O2
(molecules 15-32)
(i)
8 Ether-alkene-alcohol (alkoxy unsaturated alcohols) isomers of C4H8O2
(molecules 37-44)
(j)
Unsaturated ethers
(k)
Unsaturated hydroperoxides and unsaturated peroxides
(l) to (p)
There also
have many cyclic compounds with molecular formula
C4H8O2
(l)
Cyclic aliphatic compounds
(alicyclic compounds) based on cyclobutane
(m)
Cyclic aliphatic compounds
(alicyclic compounds) based on cyclopropane
(n)
Heterocyclic compounds based on 5 to 6 membered rings of
carbon and oxygen atoms
(o)
Heterocyclic compounds based on a 4 membered rings of
carbon and oxygen atoms
(p)
Heterocyclic compounds based on a 3 membered ring of two
carbon and one oxygen atoms
(q) to (s)
just provide extra information about the isomers of
C4H8O2
(q)
Comparison of
diagnostic prominent infrared wavenumber absorptions for selected groups of
isomers
(r)
Isomerism summary guide and exam tips
(s)
Selected comparisons of physical properties, chemical
properties and uses of isomers of C4H8O2
(t)
Practise exam questions based on the isomers of molecular
formula
C4H8O2
including: You are given
the infrared spectrum, mass spectrum, 1H NMR spectrum and 13C NMR
spectrum for an unknown molecule and one additional clue deduce the identity
and molecular structure of the molecule
Question 01 Four spectra of molecule 01, empirical
formula C2H4O *
ANSWER
(a) Introduction to this page on the isomers of C4H8O2
(and important links)
A selection of constitutional structural isomers
and stereoisomers of molecular formula
C4H8O2
So far I've identified
and described at 102 examples of constitutional isomers and at least
54 of them exhibit stereoisomerism, so there must be at least 156
distinct isomers of
C4H8O2
I'm doing
lots of new images of skeletal formulae, all numbered to match the
text.
For stereoisomers, the (CIP) abbreviation means the IUPAC Cahn-Ingold-Prelog priority
order rule for assigning E/Z (geometrical) and R/S (optical) stereoisomers.
The higher the atomic number Z, the higher the
priority e.g. 8O >
6C8O > 6C6C >
6C1H > 1H
Sections (c)
carboxylic acids and (d) esters are
typical examples of what pre-university students will encounter, but
they should be able to recognise the functional groups in many other of
the isomers.
If you think I've made an ERROR, please let me know by
EMAIL, this is a very complex case of isomerism.
Chemical composition of
C4H8O2
Percent composition by mass based on
the relative atomic masses
C= 12.01 H =
1.01 O = 16.00 and Mr(C4H8O2)
= 88.12
Element composition (to two dp): carbon = 54.52%
hydrogen = 9.17% oxygen = 36.31%
Empirical formula =
C2H4O
for molecular formula =
C4H8O2
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[privacy policy, cookies
and disclaimer]
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 isomers of formula C4H8O2
(b) Introduction to the
isomerism and selected isomers of molecular formula C4H8O2
Please
note there are a large number of isomers of molecular formula C4H8O2
and this page presents a huge selection of them and where appropriate
indicates the type of isomerism involved.
I've identified at least 102 constitutional isomers, and at least 54 pairs of
stereoisomers, therefore there are at least 156 distinct
isomers (actual or theoretical).
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, but such students should be able to recognise other
functional groups in less familiar molecules.
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 chain variation is between e.g. C-C-C-C-O and
C-O-C-C-C as well as carbon chain branching.
(b) There is positional variation e.g. the hydroxy
substituent in the aldehydes.
(c) There are lots of examples of functional group
isomerism e.g. carboxylic acids, esters, hydroxy-aldehydes,
hydroxy-ketones, alkene-alcohols (unsaturated 'enols')
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.
For stereoisomers, the (CIP) abbreviation means the
IUPAC Cahn-Ingold-Prelog priority
order rule for assigning E/Z (geometrical) and R/S (optical) stereoisomers.
There are lots of examples of
E/Z and R/S stereoisomerism
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.
There are many cases of E/Z isomerism e.g. some of the alkene-alcohols (enols) exhibit E/Z
geometrical isomerism, but there are many others in the ring
compounds.
For the pairs of E/Z isomers, the left image will be E ('trans')
and the right image Z ('cis')
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 are
many cases of R/S stereoisomerism e.g. some of the hydroxy-aldehydes can exhibit R/S
optical isomerism.
There are
complex cases where there is an overlap of E/Z and R/S isomerism for the
same constitutional isomer molecule - this is beyond the level of study
pre-university.
All the following
sections from (c) onwards deal with
detailed
descriptions of selected
constitutional structural isomers
and stereoisomers of molecular formula
C4H8O2
If you think I've made an ERROR, please let me know by
EMAIL, this is a very complex case of isomerism.
Sub-index for isomers of formula C4H8O2
(c) There are two isomeric carboxylic acids (1) to (2)
of molecular formula C4H8O2
Note that COOH is shorthand for the
carboxylic acid functional group
O=C-O-H
(1)
butanoic acid
(butyric acid),
 ,
 ,
Number of low resolution
NMR
chemical shift
δ
signal peaks: 4 1H and
4 13C
(email
if disagree?)
1H NMR ratio of peaks: 3 : 2 : 2
: 1 (for equivalent protons)
(2)
2-methylpropanoic acid (isobutyric acid),
 ,
 ,
Number of low resolution
NMR
chemical shift
δ
signal peaks: 3 1H and
3 13C
(email
if disagree?)
1H NMR ratio of peaks: 6
(3+3) : 1 : 1 (for equivalent protons)
Apart from methanoic acid (HCOOH), all other
carboxylic acids have ester functional group isomers.
Sub-index for isomers of formula C4H8O2
(d) There
are
four isomeric esters (3) to (6)
of molecular formula
C4H8O2
Note that COOC is shorthand for the ester
linkage functional group
O=C-O-C
(3)
methyl propanoate
(methyl propionate),
 ,
 ,
An ester prepared from propanoic acid and methanol.
Number of low resolution
NMR
chemical shift
δ
signal peaks: 3
1H and
4 13C
(email
if disagree?)
1H NMR ratio of peaks: 3 : 2 : 3 (for equivalent protons)
(4)
ethyl ethanoate
(ethyl acetate),
 ,
 ,
 ,
An ester prepared from ethanoic acid and ethanol.
Number of low resolution
NMR
chemical shift
δ
signal peaks: 3
1H and
4 13C
(email
if disagree?)
1H NMR ratio of peaks: 3 : 2 : 3 (for equivalent protons)
(5)
propyl methanoate (propyl formate), abbreviated structural formulae
structural formula
 ,
skeletal formula
An ester prepared from methanoic acid and
propan-1-ol.
Number of low resolution
NMR
chemical shift
δ
signal peaks: 4
1H and
4 13C
(email
if disagree?)
1H NMR ratio of peaks: 1 : 2 : 2 : 3 (for equivalent protons)
(6) 1-methylethyl methanoate
(isopropyl formate, isopropyl methanoate)
HCOOCH(CH3)2
An ester prepared from methanoic acid
formic acid) and propan-2-ol (isopropyl alcohol).
Number of low resolution
NMR
chemical shift
δ
signal peaks: 3
1H and
3 13C
(email
if disagree?)
1H NMR ratio of peaks: 1 : 1 : 6
(3+3) (for equivalent protons)
Esters are functional group isomers of carboxylic
acids.
Sub-index for isomers of formula C4H8O2
Spectra links for isomers (1) to (6)
which can be used to identify a specific isomer
The infrared spectrum of butanoic acid
(butyric acid)
The infrared spectrum of 2-methylpropanic
acid (isobutyric acid)
The infrared spectrum of methyl
propanoate (methyl propionate)
The infrared spectrum
of Ethyl ethanoate (ethyl acetate)
The infrared spectrum of propyl
methanoate (propyl formate)
The infrared spectrum of 1-methylethyl
methanoate, (propan-2-yl methanoate) (isopropyl
formate)
The mass spectrum of butanoic acid
(butyric acid)
The mass spectrum of 2-methylpropanic
acid (isobutyric acid)
The mass spectrum of methyl propanoate
(methyl propionate)
The mass spectrum of Ethyl ethanoate (ethyl
acetate)
The mass spectrum of propyl methanoate
(propyl formate)
The mass spectrum of 1-methylethyl
methanoate, (propan-2-yl methanoate) (isopropyl
formate)
The H-1
NMR spectrum of butanoic acid (butyric acid)
The H-1
NMR spectrum of 2-methylpropanic acid (isobutyric acid)
The H-1
NMR spectrum of methyl propanoate (methyl propionate)
The H-1 NMR spectrum of Ethyl ethanoate (ethyl
acetate)
The H-1
NMR spectrum of propyl methanoate (propyl formate)
The H-1
NMR spectrum of 1-methylethyl methanoate, (propan-2-yl methanoate)
(isopropyl formate)
C-13
NMR spectrum of butanoic acid (butyric acid)
The C-13
NMR spectrum of 2-methylpropanic acid (isobutyric acid)
The C-13
NMR spectrum of methyl propanoate (methyl propionate)
The C-13 NMR
spectrum of Ethyl ethanoate (ethyl
acetate)
The C-13 NMR spectrum of propyl methanoate
(propyl formate)
C-13
NMR spectrum of 1-methylethyl methanoate, (propan-2-yl methanoate)
(isopropyl formate)
Sub-index for isomers of formula C4H8O2
(e-g) For
examples (e) 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.
There are also lots
of hydroxy-aldehydes and hydroxy-ketones with a C4H8O2
molecular formula
Many
exist, others are too unstable, i.e. quoted as 'theoretical'
structures
In these abbreviated structural formulae (which you
MUST be able to interpret)
R2CO
have the >C=O carbonyl group of ketones (suffix named
-one)
and RCHO has the
H-C=O aldehyde group (suffix named
-al).
The aldehyde and ketone
functional groups have a higher ranking than the alcohol group, so the
prefix hydroxy applies
to the IUPAC names of these carbonyl molecules.
A molecule with a chiral carbon, a carbon attached to
four different groups or atoms, will exhibit R/S
stereoisomerism, exhibiting R/S isomers, optical isomers -
non-superimposable mirror image forms known as enantiomers.
Sub-index for isomers of formula C4H8O
(e) The
5 hydroxy-aldehyde isomers of molecular formula
C4H8O2
These have two functional groups: aldehyde
(R-CHO) and
alcohol-hydroxy (C-OH)
(7) CH3CH2CH(OH)CHO,
2-hydroxybutanal
(8) CH3CH(OH)CH2CHO,
3-hydroxybutanal, R/S isomers, C3 is chiral
(9) HOCH2CH2CH2CHO,
4-hydroxybutanal, does NOT exhibit R/S isomerism
(10)
(CH3)2C(OH)CHO,
2-hydroxy-2-methylpropanal, does NOT exhibit R/S isomerism
(11) HOCH2CH(CH3)CHO,
3-hydroxy-2-methylpropanal, R/S isomers, C2 is chiral
All five hydroxy-aldehydes are illustrated
with names and skeletal (below), just skeletal formula (above)
The skeletal formula of 2-hydroxybutanal, 3-hydroxybutanal,
4-hydroxybutanal, 2-hydroxy-2-methylpropanal, 3-hydroxy-2-methylpropanal,
indicating R/S isomers (optical isomerism) deduced from the molecular
structure.
Sub-index for isomers of formula C4H8O2
(f) The 3 hydroxy-ketone isomers of molecular formula C4H8O2
The ketone group takes priority over the alcohol group in
naming these hydroxy-ketones (IUPAC nomenclature rule)
These have two functional groups: ketone
(O=CR2, R
not H) and alcohol-hydroxy (C-OH)
(12)
CH3CH2COCH2OH, 1-hydroxybutan-2-one (1-hydroxy-2-butanone,
1-hydroxybutanone)
(13)
CH3CH(OH)COCH3,
3-hydroxybutan-2-one (3-hydroxy-2-butanone, 3-hydroxybutanone),
(13) exhibits R/S isomers,
C3 is chiral, ketone is higher ranking than alcohol.
(14)
HOCH2CH2COCH3,
4-hydroxybutan-2-one (4-hydroxy-2-butanone, 4-hydroxybutanone)
All three hydroxy-ketones are
also illustrated below with names.
The skeletal formula of 1-hydroxybutan-2-one (1-hydroxy-2-butanone,
2-hydroxybutanone), 3-hydroxybutan-2-one (3-hydroxy-2-butanone,
3-hydroxybutanone), 4-hydroxybutan-2-one, indicating R/S isomers (optical
isomerism) deduced from the molecular structure.
Sub-index for isomers of formula C4H8O2
(g)
3 Ether-carbonyl compounds - methoxy-aldehydes/ketones and
an ethoxy aldehyde
These have two functional groups: aldehyde
(O=C-H, CHO) and ether
linkage (C-O-C, COC)
(33) 2-ethoxyethanal,
CH3CH2OCH2CHO
(34) 2-methoxypropanal,
CH3OCH(CH3)CHO,
R/S isomers, C2 is chiral
(35) 3-methoxypropanal,
CH3OCH2CH2CHO
(36) 1-methoxypropan-2-one,
CH3COCH2OCH3, (1-methoxy-2-propanone,
1-methoxypropanone)
Sub-index for isomers of formula C4H8O2
(h) 18 E ne-diols
(18 unsaturated diols)
with molecular formula
C4H8O2
e.g. examples of molecules with two hydroxy groups (diol) and an
alkene group.
In the following examples note that the OH (hydroxy, ol)
group is a higher ranking group than the >C=C< 'ene' group, so diol is
the suffix in the name.
The isomers here are due changing the position of the OH
(hydroxy) and C=C (ene) in a linear for carbon chain.
Some of these unsaturated
diols will be very unstable and might not exist at all.
The E/Z (geometrical) isomers
arise from the restricted rotation of the >C=C< double bond.
There are probably many
examples of keto-enol isomerisation (tautomerism) via
-C(OH)=C<
-CO-CH< (an unsaturated
alcohol forming an aldehyde or ketone)
Examples based on but-1-ene (but not the priority in the IUPAC compound name)
These all have two functional groups: an alkene (>C=C<)
and two alcohol groups (2 x hydroxy
-OH, diol)
(15)
(HO)2C=CHCH2CH3
but-1-ene-1,1-diol (1-butene-1,1-diol), not E/Z isomerism
Theoretical highly unstable, two OH groups attached
to same carbon atom.
(16)
HOCH=C(OH)CH2CH3
but-1-ene-1,2-diol (1-butene-1,2-diol), E/Z isomerism
CIP assignment priority rule for E/Z isomers:
8O >
6C > 1H (about
the >C=C< double bond)
(17)
HOCH=CHCH(OH)CH3
but-1-ene-1,3-diol (1-butene-1,3-diol)
Complex stereoisomerism, an overlap of E/Z and
R/S isomerism, C3 is chiral.
CIP assignment priority rule for E/Z isomers:
8O >
6C > 1H (about
the >C=C< double bond)
Likely to undergo keto-enol isomerisation
(tautomerism) to give 3-hydroxybutanal
HOCH=CHCH(OH)CH3
OHCCH2CH(OH)CH3
(18)
HOCH=CHCH2CH2OH
but-1-ene-1,4-diol (1-butene-1,3-diol), E/Z isomerism
As for (17) above, might well tautomerise to
4-hydroxybutanal.
CIP assignment priority rule for E/Z isomers:
8O >
6C > 1H (about
the >C=C< double bond)
(19)
CH2=C(OH)CH(OH)CH3
but-1-ene-2,3-diol (1-butene-2,3-diol),
R/S isomers (BUT not E/Z isomerism),
C3 is chiral
Again this might undergo keto-enol isomerisation to
3-hydroxybutanone
CH2=C(OH)CH(OH)CH3
CH3COCH(OH)CH3
(20)
CH2=C(OH)CH2CH2OH
but-3-ene-1,3-diol (3-butene-1,3-diol),
R/S isomers (BUT not E/Z isomerism),
C3 is chiral
Does NOT exhibit R/S
isomerism or E/Z isomerism
Again this might undergo keto-enol isomerisation to
4-hydroxybutan-2-one
CH2=C(OH)CH2CH2OH
CH3COCH2CH2OH
(21)
CH2=CHCH(OH)CH2OH
but-3-ene-1,2-diol (3-butene-1,2-diol)
R/S isomers (BUT not E/Z isomerism),
C2 is chiral
(22)
CH2=CHC(OH)2CH3
but-3-ene-2,2-diol (3-butene-2,2-diol), no E/Z or R/S isomerism.
(23)
CH2=CHCH2CH(OH)2
but-3-ene-1,1-diol (3-butene-1,1-diol), no E/Z or R/S isomerism
Theoretical highly unstable, two OH groups attached
to the same end carbon atom.
Some of these alkene-diols are
also illustrated below as their skeletal formula, note the E/Z isomerism
Skeletal formula of but-1-ene-1,2-diol (1-butene-1,2-diol),
but-1-ene-1,3-diol (1-butene-1,3-diol), but-1-ene-1,4-diol
(1-butene-1,3-diol), but-3-ene-1,2-diol
(3-butene-1,2-diol), but-3-ene-1,3-diol (3-butene-1,3-diol), R/S isomers,
E/Z isomers, some exhibit keto-enol tautomerism R/S isomerism or E/Z
isomerism deduced from the molecular structure.
Sub-index for isomers of formula C4H8O2
Examples based on but-2-ene (but not the priority in the
IUPAC compound name)
These all have two functional groups: an alkene (>C=C<)
and two alcohol groups (2 x hydroxy
-OH, diol)
(24)
CH3CH=CHCH(OH)2
but-2-ene-1,1-diol (2-butene-1,1-diol),
E/Z isomerism
CIP assignment priority rule for E/Z isomers:
6C > 1H
(about the >C=C< double bond)
(25)
HOCH2C(OH)=CHCH3
but-2-ene-1,2-diol (2-butene-1,2-diol), E/Z isomerism
CIP assignment priority rule for E/Z isomers:
8O >
6C > 1H (about
the >C=C< double bond)
May exhibit
keto-enol
tautomerism, likely to isomerise to 1-hydroxybutan-2-one)
(26)
HOCH2CH=C(OH)CH3
but-2-ene-1,3-diol (2-butene-1,3-diol), E/Z isomerism
CIP assignment priority rule for E/Z isomers:
8O >
6C > 1H (about
the >C=C< double bond)
(27)
HOCH2CH=CHCH2OH
but-2-ene-1,4-diol (2-butene-1,4-diol), E/Z isomerism
CIP assignment priority rule for E/Z isomers:
6C > 1H
(about the >C=C< double bond)
(28)
CH3C(OH)=C(OH)CH3
but-2-ene-2,3-diol (2-butene-2,3-diol), E/Z isomers (exhibits
keto-enol
tautomerism)
CIP assignment priority rule for E/Z isomers:
8O >
6C (about the >C=C< double bond)
May exhibit
keto-enol isomerisation and form 3-hydroxybutan-2-one
Their skeletal formula are
shown below with names.
The skeletal formula of but-2-ene-1,2-diol
(2-butene-1,2-diol), E/Z isomerism, but-2-ene-1,3-diol (2-butene-1,3-diol), but-2-ene-1,4-diol (2-butene-1,4-diol)
and but-2-ene-2,3-diol and examples of E/Z isomerism and keto - enol
tautomerism deduced from the molecular structure.
Sub-index for isomers of formula C4H8O2
Examples based on
2-methylpropene
(again, the IUPAC priority group name is the diol)
These all have two functional groups: an alkene (>C=C<)
and two alcohol groups (2 x hydroxy
-OH, diol)
(29) (HO)2C=C(CH3)2
2-methylprop-1-en-1,1-diol, highly unstable, unlikely to exist
(30)
HOCH=C(CH3)CH2OH
2-methylprop-1-en-1,3-diol,
exhibits E/Z isomerism
CIP assignment priority rule for E/Z isomers:
8O >
6C > 1H (about
the >C=C< double bond)
It may undergo keto-enol isomerisation to give
the more stable 3-hydroxy-2-methylpropanal
(31)
H2C=C(CH3)CH(OH)2
2-methylprop-2-en-1,1-diol,
highly unstable, unlikely to exist
(32)
H2C=C(CH2OH)2
2-(hydroxymethyl)prop-2-en-1-ol
You can't have
2-methylprop-1-ene-1,2-diol, can you see why?
Their theoretical skeletal formulae are shown below (I don't
think they are stable enough to exist?
The skeletal formulae of 2-methylprop-1-ene-1,1-diol
(NO E/Z isomers) and
2-methylprop-1-ene-1,3-diol (will theoretically exhibit E/Z isomerism).
Sub-index for isomers of formula C4H8O2
(i)
Ether-alkene-alcohols (alkoxy unsaturated alcohols) (37-44) e.g.
These have three functional groups:
alkene (>C=C<),
alcohol group (hydroxy
-OH)
and ether linkage (C-O-C)
(37) 1-methoxyprop-1-en-1-ol,
CH3CH=C(OH)OCH3
or
CH3CH=C(OCH3)OH,
E/Z
isomers, From the CIP assignment priority rule for E/Z isomers:
8O >
6C > 1H
(for atoms
and groups about the >C=C< double bond)
(38) 2-methoxyprop-1-en-1-ol,
CH3OC(CH3)=CHOH or CH3C(OCH3)=CHOH,
E/Z isomers, From the CIP assignment priority rule for
E/Z isomers:
8O >
6C > 1H
(for atoms and groups about the >C=C< double
bond)
Might undergo keto-enol isomerisation to form
2-methoxypropanal.
(39) 3-methoxyprop-1-en-1-ol,
CH3OCH2CH=CHOH,
E/Z geometrical isomers
From the CIP assignment priority rule for
E/Z isomers:
8O6C >
8O1H > 6C >
1H
(for atoms and groups about the >C=C< double
bond)
Might undergo keto-enol isomerisation to form
3-methoxypropanal.
(40) 1-methoxy-prop-1-en-2-ol,
HOC(CH3)=CHOCH3,
E/Z isomers, From the CIP assignment priority rule for
E/Z isomers:
8O >
6C > 1H
(for atoms and groups about the >C=C< double
bond)
(41) 2-methoxyprop-1-en-2-ol,
CH3OCH2C(OH)=CH2
Might undergo keto-enol isomerisation to form
1-methoxypropanone
(42)
1-methoxyprop-2-en-2-ol,
HOCH(OCH3)CH=CH2,
R/S isomers
(enantiomers), C2 is chiral
(43) 2-methoxyprop-2-en-1-ol,
HOCH(OCH3)CH=CH2
(44) 3-methoxyprop-2-en-1-ol,
HOCH2CH=CHOCH3
E/Z isomers, From the CIP assignment priority rule for
E/Z isomers:
8O >
6C > 1H
(for atoms and groups about the >C=C< double
bond)
Sub-index for isomers of formula C4H8O2
(j) Unsaturated ethers
('di-ethers')
One functional group: a double ether linkage (-C-O-C-
x 2)
For the pairs of E/Z isomers, the left image is E ('trans')
and the right image Z ('cis')
Both of these are known to exist.
(45) 1,1-dimethoxyethene,
CH2=C(OCH3)2
(46) 1,2-dimethoxyethene,
CH3OCH=CHOCH3
CIP assignment priority rule for E/Z isomers:
8O > 1H
(for atoms and groups about the >C=C< double bond)
Sub-index for isomers of formula C4H8O2
(k)
Organic unsaturated
hydroperoxides and unsaturated peroxides
I've no idea which of them exist?
From the CIP assignment priority rule for the E/Z
isomers below:
8O >
6C8O > 6C6C >
6C1H > 1H
(for atoms and groups about the >C=C< double bond)
For the pairs of E/Z isomers, the left image is E ('trans')
and the right image Z ('cis')
(47) to (54) are organic unsaturated hydroperoxides, I
don't know if any exist?
(47) CH3CH2CH=CHOOH,
but-1-en-1-yl hydroperoxide ?, E/Z 'geometrical' isomers
(48) CH3CH2C(OOH)=CH2,
name ?
(49) CH3CH(OOH)CH=CH2,
but-1-en-2-yl hydroperoxide, R/S 'optical' isomers (enantiomers),
(50) HOOCH2CH2CH=CH2,
3-butenyl hydroperoxide ?
(51) CH3CH=CHCH2OOH,
but-2-en-1-yl
hydroperoxide ?, E/Z isomers
(52) CH3CH=C(OOH)CH3,
but-2-en-2-yl
hydroperoxide ?, E/Z isomers
(53)
(CH3)2C=CHOOH,
2-methyl-1-propen-1-yl hydroperoxide, (2-methyl-1-propen-1-yl
hydroperoxide),
(54) HOOCH(CH3)CH=CH2,
name ?
(55) to (56) are organic unsaturated peroxides, I don't
know if any exist?
(55) CH3CH2OOCH=CH2,
name ?
(56) CH3OOCH2CH=CH2,
name ?
(57) CH3OOCH=CHCH3,
name ?, E/Z isomers
Sub-index for isomers of formula C4H8O2
(l) to (p) There also many cyclic compounds with molecular formula
C4H8O2
(l) Cyclic aliphatic compounds
(alicyclic compounds) based on cyclobutane
(58) cyclobutane-1,1-diol,
probably very unstable, no stereoisomers, has plane of symmetry.
(59)
cyclobutane-1,2-diol,
stable, both E/Z (geometrical) isomers and R/S (optical) isomers,
both C1 and C2 are chiral, but they also form the
stereocentre for E/Z isomerism.
The E 'trans' isomer can form a pair of enantiomers, and
the Z 'cis' isomer is an achiral ('meso') isomer and optically inactive
due to having a plane of symmetry.
(60) cyclobutane-1,3-diol,
stable, Overlap of E/Z and R/S stereoisomers (complex stereoisomerism!).
(61) cyclobutyl
hydroperoxide, cyclobutane hydroperoxide, highly unstable, highly
reactive compound.
The skeletal formula of cyclobutane-1,2-diol (Z,
cis isomer) and
cyclobutane-1,3-diol (E, trans isomer),
both are derived from two hydroxyl OH substituents in the cyclobutane molecule and
both theoretically exhibit E/Z and R/S isomerism (but complicated),
this diagram indicates the more correct 3D shape - maximising the C-C-C and
H-C-C bond angles.
Sub-index for isomers of formula C4H8O2
(m) Cyclic aliphatic compounds
(alicyclic compounds) based on cyclopropane
(62) 2-methylcyclopropane-1,1-diol,
R/S isomers, bottom right carbon of
Δ
(C2) is chiral.
(63) 1-methylcyclopropane-1,2-diol,
complex isomerism, overlap of E/Z and R/S isomerism.
(64) 3-methylcyclopropane-1,2-diol,
complex isomerism, overlap of E/Z and R/S isomerism.
(65) name ?, R/S optical isomers, bottom right carbon of
Δ
(C1) is chiral.
(66) name ?, complex isomerism, overlap of E/Z and R/S
isomerism.
(67) name ?
(68) 1-methoxycyclopropan-1-ol,
ether linkage (C-O-C)
and alcohol (C-OH)
functional groups
(69)
2-methoxycyclopropanol,
ether linkage (C-O-C)
and alcohol (C-OH)
functional groups
Complex isomerism, overlap of E/Z and R/S isomerism.
(70) an organic hydroperoxide, name ?
(71) an organic hydroperoxide, name ?
(72) an organic hydroperoxide, name ?
(73) an organic peroxide, name ?
(74) name ?, ether linkage (C-O-C)
and alcohol (C-OH)
functional groups
Sub-index for isomers of formula C4H8O2
(n)
Heterocyclic compounds based on 5 to 6 membered rings of carbon and oxygen atoms
e.g.
where the C and O atoms form a hexagonal or pentagonal ring.
(75)
1,2-dioxane (cyclic organic peroxide)
(76)
1,3-dioxane
(cyclic ether)
(77)
1,4-dioxane
(cyclic ether)
(78)
3-methyl-1,2-dioxolane,
R/S optical isomers, bottom right carbon is chiral
(79)
4-methyl-1,2-dioxolane
(80)
2-methyl-1,3-dioxolane
(81)
4-methyl-1,3-dioxolane,
R/S optical isomers, bottom left carbon is chiral
(82)
oxolan-2-ol,
R/S optical isomers, top right carbon is chiral
(83)
oxolan-3-ol,
R/S optical
isomers, bottom right carbon is chiral
Sub-index for isomers of formula C4H8O2
(o)
Heterocyclic compounds based on a 4 membered rings of carbon and oxygen atoms
(84) 3,3-dimethyl-1,2-dioxitane, name ?
(85)
3,4-dimethyl-1,2-dioxitane, name ?,
complex stereoisomerism, overlap of E/Z and R/S isomers.
(86)
2,2-dimethyl-1,3-dioxitane,
name ?
(87)
2,4-dimethyl-1,3-dioxitane,
name ?, E/Z geometrical isomers (R/S isomers ?)
(88)
name ?, R/S optical isomers, bottom right carbon of
□
is chiral.
(89)
2-methyloxetan-3-ol,
name ?, complex stereoisomerism, overlap of E/Z and R/S isomers.
(90)
4-methyloxetan-2-ol,
name ? complex
stereoisomerism, overlap of E/Z and R/S isomers.
(91)
[oxetan-2-yl]methanol,
R/S isomers, bottom right carbon
of □
is chiral,
(92) 3-methyloxetan-2-ol,
name ?, complex stereoisomerism, overlap of E/Z and R/S isomers.
(93)
3-methyloxetan-3-ol,
name ?
(94)
[oxetan-3-yl]methanol,
name ?
Sub-index for isomers of formula C4H8O2
(p) Heterocyclic compounds based on a 3
membered ring of two carbon and one oxygen atoms
(95)
1-ethyloxiranol,
name ?, R/S optical isomers, bottom right C of
Δ
is chiral.
(96)
2-ethyloxiranol,
name ?, complex isomerism, overlap of E/Z and R/S isomers,
both
carbon atoms of the
Δ
are chiral
(97)
2-(oxiran-2-yl)ethan-1-ol
(98)
name ?
(99)
[2-methyloxiran-2-yl]methanol
(100)
(3-methyloxiran-2-yl)methanol, complex isomerism, overlap of E/Z and R/S
isomers,
both carbon atoms of the
Δ
are chiral
(101)
1,2-dimethyloxiranol,
name ?, , complex isomerism, overlap of E/Z and R/S isomers,
both carbon atoms of the
Δ
are chiral
(102)
2,2-dimethyloxiranol,
name ?, R/S optical isomers, bottom left C of
Δ
is chiral.
Sub-index for isomers of formula C4H8O2
(q) Comparison of
diagnostic prominent infrared wavenumber absorptions for selected groups of isomers of C4H8O2
Infrared spectra: Adding alkene-diols to the mix makes this a
beautifully rich IR comparison.
These compounds introduce C=C stretches and –OH groups,
often with subtle shifts due to conjugation or intramolecular hydrogen
bonding.
Most of this extra information is aimed at carboxylic acids,
esters, aldehydes, ketones and unsaturated diols.
Prominent IR Absorptions of C4H8O2 Isomers
|
Isomer Type |
Example Structure |
Key Functional Groups |
Diagnostic IR Peaks (cm⁻¹) |
Notes & Tips |
|
Carboxylic Acid |
Butanoic acid |
–COOH |
- Broad O–H stretch: 2500–3300
(very broad)
- C=O stretch: 1700–1725 |
Acid O–H is ragged and extends lower than
alcohols due to strong H-bonding |
|
Ester |
Methyl propanoate |
–COOR |
- C=O stretch: 1735–1750
(sharp)
- C–O stretch: 1050–1300 |
C=O is higher than acids; C–O often shows two
bands, useful for confirmation |
|
Hydroxyketone
and hydroxyaldehydes |
3-Hydroxybutanone |
–OH and C=O |
- O–H stretch: 3200–3600
(broad)
- C=O stretch: 1715–1725 |
Can resemble acid spectra; look for absence of
low-end O–H tail |
|
Alkene-Diol |
But-2-ene-1,4-diol |
C=C and –OH ×2 |
- C=C stretch: 1600–1680
(medium)
- O–H stretch: 3200–3600
- C–O: 1000–1200 |
C=C often weak; conjugation or H-bonding can
shift O–H and C=C slightly |
Common Misconceptions
about the infrared spectra of isomers of
C4H8O2
(see also below)
-
Missing weak C=C stretches: Alkenes often
show weak or absent C=C peaks, especially if symmetrical.
-
Confusing alkene-diols with hydroxycarbonyls:
Lack of C=O is the giveaway.
-
Assuming all broad O–H stretches are acids:
Diols and alkene-diols also show broad O–H, but without the low-end tail.
-
Overlooking conjugation effects: C=C and
C=O stretches can shift if conjugated with –OH or other groups.
Exam Tips for questions
that may involve the
infrared spectra of isomers of C4H8O2
(see also above)
-
Check for C=O first: Its presence or
absence narrows down possibilities dramatically.
-
Use C=C stretch cautiously: It’s often weak
and easily missed; confirm with structure or other data.
-
Broad O–H: overlaps with C-H vibrations.
-
C–O stretches are underrated: Especially in
esters, diols, and alkene-diols - they help distinguish between similar
spectra.
-
Sketch and annotate: Especially useful when
comparing alkene-diols versus hydroxycarbonyls.
Sub-index for isomers of formula C4H8O2
(r) Summary Guide to
C4H8O2
Isomerism and Exam Preparation
This guide covers all isomerism types for
C4H8O2, compares their
physical and chemical behaviour, outlines relative reactivity, details
real‐world applications, highlights common student misconceptions, and provides
tailored revision tips for AQA, Edexcel, OCR, WJEC, CCEA, CIE, and IB exams.
I've sometimes added comment about molecules
unlikely to encounter in pre-university courses.
1.
Types of Isomerism in
C4H8O2
1.1 Structural (Constitutional)
Isomerism
-
Chain isomerism: different carbon skeletons (straight versus
branched) – butanoic acid versus 2-methylpropanoic acid.
-
Functional-group isomerism: carboxylic acids versus esters
(–COOH versus –COOR).
-
Positional isomerism (esters only): e.g. methyl propanoate
versus propyl formate – same functional group but R and acyl fragments swap
positions.
1.2 Stereoisomerism
Quite a few examples of E/Z (geometrical) isomerism e.g.
unsaturated diols, and 'scattered' examples of R/S (optical) isomerism.
1.3 Ring–Chain Isomerism
Lots of examples, both alicyclic and heterocyclic (quite a
range of 3-6 membered ring compounds), but less likely to be encountered
pre-university.
Sub-index for isomers of formula C4H8O2
(s) 2.
Physical Property Comparisons
of selected isomers of
C4H8O2
| Property |
Carboxylic Acids |
Esters |
| Boiling point |
High (e.g. butanoic acid 163.5
°C) |
Significantly lower (e.g.
ethyl acetate ≈ 77 °C) |
| Hydrogen bonding |
Strong (dimer formation) |
None (no –OH) |
| Solubility in water |
Miscible at low mol %
(H-bonding) |
Limited (dipole only) |
| Odour |
Pungent, rancid-butter like |
Fruity, pleasant |
3.
Chemical Reaction Differences
of selected isomers of
C4H8O2
-
Carboxylic acids
-
Acid–base: neutralise with alkali to give carboxylate
salts (e.g. RCOOH + NaOH → RCOO-Na+ + H2O
-
Esterification: react with alcohols under acid catalysis
to form esters.
-
Conversion to acyl chlorides, anhydrides.
-
Esters
-
Acid- and base-catalysed hydrolysis (saponification)
back to acids and alcohols.
-
Transesterification: exchange of R group under
catalysis.
-
Reduction to primary alcohols (LiAlH4).
4.
Relative Reactivity Trends
|
Functional
Group |
Reactivity in
Acyl Substitution |
|
Acid chloride >
Anhydride |
> Ester >
Carboxylic acid |
|
Leaving-group
ability |
Cl⁻ > RCOO⁻ >
RCOOH |
In practice, carboxylic acids and esters are far less reactive than acid
chlorides.
5.
Uses and Applications
of selected isomers of
C4H8O2
-
Butanoic Acid (n-butyric acid)
-
Food flavouring (buttery notes) and fragrance
intermediate.
-
Pharmaceutical precursor (analgesics, antiseptics).
-
Perfumery, animal-feed additive, industrial solvent, and
potential biofuel feedstock.
-
2-Methylpropanoic Acid (isobutyric acid)
-
Esters (general C4H8O2 family)
-
Methyl propanoate and ethyl ethanoate: common solvents in
paints, coatings, decaffeination, and chromatography.
-
Propyl methanoate and isopropyl methanoate: flavour and
fragrance agents in food and cosmetic products.
6.
Common Student Misconceptions
about isomers of
C4H8O2
-
Confusing chain versus functional-group isomers - always check
connectivity, not just formula.
-
Believing all C4H8O2 isomers are liquids with similar
bps - remember H-bonding in acids elevates boiling points.
-
Overlooking ester hydrolysis conditions versus acid–base
neutralisation.
-
Assuming optical or geometric isomerism exists - verify
presence of C=C or chiral centres.
7.
Exam Revision Tips for questions that
may involve
the isomers of
C4H8O2
-
Tabulate boiling points, solubilities, and IR peaks (–OH
versus C=O versus C–O–C).
-
Practice naming all six carboxylic acid and ester isomers by IUPAC.
-
Use NMR predictions to distinguish acid versus ester
(exchangeable OH versus quartet/triplet patterns).
-
Memorise fingerprint IR region: carboxylic acids (broad
2500–3300 cm⁻¹), esters (~1735 cm⁻¹ sharp).
Sub-index for isomers of formula C4H8O2
Learning objectives - questions to be answered?
You should be able to
fully analyses and name the carboxylic acids and esters of molecular
formula C4H8O2
However, you should be able to
recognise in most of the structures displayed above, the functional groups
carboxylic acids, esters, aldehydes, ketones, alcohols, alkenes and ethers of
molecular formula C4H8O2
BUT, bear in mind, many of the isomers have two of the above
functional groups.
How do you work out the structure
of the isomers of molecular formula C4H8O2?
How do you draw the structural
formula and skeletal formula of the isomers of molecular formula
C4H8O2?
How do you name the isomers of molecular formula
C4H8O2?
How many aliphatic structural
isomers are there of molecular formula C4H8O2?
How many aliphatic carbon chain
isomers are there of molecular formula C4H8O2?
How many positional isomers are
there of molecular formula C4H8O2?
Are there any
aliphatic open chain alkene isomers of molecular formula C4H8O2?
Are there any carboxylic acid isomers of
molecular formula C4H8O2?
Are there any ester
isomers of molecular formula C4H8O2?
Are there any
alkene-alcohol enol isomers of molecular formula C4H8O2?
Are there any alkene isomers of molecular formula
C4H8O2?
Are there any alcohol isomers of molecular formula
C4H8O2?
Are there any aldehyde isomers of molecular formula
C4H8O2?
Are there any ketone isomers of molecular formula
C4H8O2?
Are there any functional group
isomers with a molecular formula C4H8O2?
Does C4H8O2 have any stereoisomers?
Are there any E/Z (geometrical)
isomers with a molecular formula C4H8O2?
Are there any R/S (optical) isomers
(enantiomers) with a molecular formula C4H8O2?
How many E/Z (geometrical) isomers
are there of molecular formula C4H8O2?
How many R/S (optical) isomers
(enantiomers) of molecular formula C4H8O2?
This page will answer these questions
for molecular formula C4H8O2
Sub-index for isomers of formula C4H8O2
|
QUESTIONS
(t)
Practise exam questions based on the isomers of molecular
formula C6H14
I don't mind if students/teachers do a selected printout of
these questions and answers.
The questions are designed for UK advanced A-level chemistry
students (US grades 11-12).
Jot down your responses and check out the
ANSWERS with explanation.
If you think there is an error, please email me asap at
chem55555@hotmail.com
Given the structural formulae of six of the isomers of molecular
formula C4H16 for each question
answer provide brief reasoning.
|
(A)
CH3CH(OH)CH2CHO |
(B)
HOCH=C(CH3)CH2OH |
(C)
CH3OCH2CH2CHO |
|
(D) (CH3)2CHCOOH |
(E)
HOCH2CH2COCH3 |
(F) CH3CH2COOCH3 |
For
each question answer provide brief reasoning.
Q1 Which isomer(s) of C4H8O2
is/are alcohols? Classification?
Q2 Which isomer(s) of C4H8O2
can exhibit E/Z (geometrical) isomerism
Q3 Which isomer(s) of C4H8O2
is/are ketones?
Q4 Which isomer(s) of C4H8O2
is/are esters?
Q5 Which isomer(s) of C4H8O2
can be 'mildly' oxidised to a ketone?
Q6 Which isomer(s) of C4H8O2
can only exhibit three 1H and three 13C
NMR principal chemical shift signals?
Q7 Which isomer(s) of C4H8O2
is/are carboxylic acid
Q8 Which isomer(s) of C4H8O2
can be 'mildly' oxidised to an aldehyde?
Q9 Which isomer(s) of C4H8O2
can exhibit R/S (optical) isomerism
Q10 Give the IUPAC
name for A to F.
Q11 You are given
the infrared spectrum, mass spectrum, 1H NMR spectrum and 13C NMR
spectrum for an unknown molecule and one additional clue deduce the identity
and molecular structure of the molecule
Question 01 Four spectra of molecule 01, empirical
formula C2H4O *
ANSWER
Jot down your responses and check out the
ANSWERS with explanation.
If you think there is an error, please email me asap at
chem55555@hotmail.com
|
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
Sub-index for isomers of formula C4H8O2
Index of my advanced
(pre-college/university) organic
chemistry revision notes
The
main index for all my spectroscopy pages
The
main index for 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
|
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The isomerism of molecular formula C4H8O2.
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chemistry students taking the WJEC advanced A level chemistry, CCEA
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Keywords or phrases: how many isomers are
there of molecular formula C4H8O2? how do you name the isomers of
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isomers of C4H8O2, what type of isomerism is exhibited by molecules
of formula C4H8O2, how do you work out the isomers of molecular
formula C4H8O2, what are the structural isomers of C4H8O2, the carbon chain
isomers of C4H8O2 in the homologous series of alkanes, comparing
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isomerism of C4H8O2 molecules, isomerism in
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the isomers of C4H8O2
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skeletal formula of isomers of C4H8O2, how to name the isomers
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isomers of C4H8O2 of molecular mass 88 carboxylic acid molecules isomeric of molecular formula C4H8O2, ester molecules isomeric with molecular formula C4H8O2, ketones hydroxyketones isomeric with molecular formula C4H8O2, aldehydes hydroxyaldehydes isomeric with molecular formula C4H8O2, alkenediols isomeric with molecular formula C4H8O2, structural isomers of molecular formula C4H8O2, optical isomers R/S enantiomers isomeric with molecular formula C4H8O2, positional isomers isomeric with molecular formula C4H8O2, which types of isomerism are exhibited by molecules isomeric with molecular formula C4H8O2
Diagrams of
the structure
of the isomers of C4H8O2, Drawings the structural
formula and skeletal formula of the isomers of C4H8O2, names of the isomers of
C4H8O2, structural isomers are of C4H8O2, the number of carboxylic acid isomers of
C4H8O2, number of ester
isomers of C4H8O2, the alkene-alcohol enol isomers of C4H8O2, the alkene isomers of
C4H8O2, alcohol isomers of C4H8O2? the aldehyde isomers of
C4H8O2, the ketone isomers of C4H8O2, the any functional group
isomers with a C4H8O2 the stereoisomers of C4H8O2,
the E/Z geometrical
isomers of C4H8O2, the
R/S optical isomers (enantiomers) of C4H8O2
Sub-index for isomers of formula C4H8O2
|
ANSWERS
I don't mind if students/teachers do a selected printout of
these questions and answers.
Practise exam questions based on the isomers of molecular
formula C6H14
The questions are designed for UK advanced A-level chemistry
students (US grades 11-12).
If you think there is an error, please email me asap at
chem55555@hotmail.com
Given the structural formulae of six of the isomers of molecular
formula C4H16 for each question
answer provide brief reasoning.
|
(A)
CH3CH(OH)CH2CHO |
(B)
HOCH=C(CH3)CH2OH |
(C)
CH3OCH2CH2CHO |
|
(D) (CH3)2CHCOOH |
(E)
HOCH2CH2COCH3 |
(F) CH3CH2COOCH3 |
For
each question answer provide brief reasoning.
Q1 Which isomer(s) of C4H8O2
is/are alcohols? Classification?
ANSWER:
A (secondary),
B (primary, C3)
and E (primary)
Q2 Which isomer(s) of C4H8O2
can exhibit E/Z (geometrical) isomerism
ANSWER:
B, 2 different groups bonded to each carbon of a >C=C< alkene bond
system
Q3 Which isomer(s) of C4H8O2
is/are ketones?
ANSWER:
E C-C(=O)-C, C-CO-C
grouping
Q4 Which isomer(s) of C4H8O2
is/are esters?
ANSWER:
F -COOC- linkage
Q5 Which isomer(s) of C4H8O2
can be 'mildly' oxidised to a ketone?
ANSWER:
A, secondary alcohol
Q6 Which isomer(s) of C4H8O2
can only exhibit three 1H and three 13C
NMR principal chemical shift signals?
ANSWER:
D, all the others have at least one quartet of 1H or
13C NMR signals
Q7 Which isomer(s) of C4H8O2
is/are carboxylic acid
ANSWER:
D, -COOH group
Q8 Which isomer(s) of C4H8O2
can be 'mildly' oxidised to an aldehyde?
ANSWER:
B (C1) and E
(C4), oxidation of primary alcohol groups to aldehyde.
Q9 Which isomer(s) of C4H8O2
can exhibit R/S (optical) isomerism
ANSWER:
A, the only molecule with an asymmetric chiral carbon atom (C3)
with four different groups attached to the same carbon atom.
Q10 Give the IUPAC
name for A to F.
(A) 3-hydroxybutanal, (B)
2-methylprop-1-en-1,3-diol (university level), (C)
3-methoxypropanal
(D) 2-methylpropanoic acid, (E)
4-hydroxybutan-2-one, (F)
methyl propanoate
Q11 You are given
the infrared spectrum, mass spectrum, 1H NMR spectrum and 13C NMR
spectrum for an unknown molecule and one additional clue deduce the identity
and molecular structure of the molecule
Question 01 Four spectra of molecule 01, empirical
formula C2H4O *
ANSWER
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Sub-index for isomers of formula C4H8O2
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