Mohammed Salam Unit 14: LA C
Designing molecules
What is structural isomerism?
The following section examines some of the ways structural isomers can form, and it shows that the
atoms in structural isomerism are arranged completely differently. In drawing isomers, it is
important to be familiar with the various forms of structural isomerism.
Chain:
These isomers are possible due to carbon chains' capability of branching, for instance, butane has
two isomers, C4H10, in which one of the chains is straight and the other is branched.
These two images are a type of chain isomers. The first one is pentane which is a straight chain
isomer since its carbons are going in straight whereas the second image this is a 2,2 – dimethyl
propane which is a branched chain since two carbons are attached one carbon is situated above and
one is located at the bottom of the second carbon. In total, both images show that they have five
carbons.
Difference in properties:
There are few differences of properties in pentane and 2,2 – dimethyl propane like the boiling point
of pentane is 36 degrees whereas the 2,2 – dimethyl propane the boiling point 9 degrees. Pentane
boiling point is much more higher than 2,2 – dimethyl propane because pentane molecule features
stronger force of attraction than 2,2 – dimethyl propane and therefore more energy is required to
overcome. 2,2 dimethyl propane is insoluble to water but soluble to alcohol whereas the pentane is
soluble in water. The intermolecular force is greater in pentane because it is a straight chain alkane
so it will also have more surface area than 2,2 dimethyl propane.
Positional:
In position isomerism, the underlying carbon skeleton remains unchanged, but essential groups are
moved. The chemical formula C3H7Br, for instance, has two structural isomers. On one of them, the
bromine atom resides at the end, and on the other, it is positioned in the middle.
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,Mohammed Salam Unit 14: LA C
These images that are shown are positional isomers like the first one, the chlorine is located with the
first carbon whereas the second picture shows that the chlorine is located in between the first and
second carbon. These images show that they have the same molecular formula but the atoms in
arrangement of space are structured differently.
Difference in properties:
1 – chlorobutane has a boiling point of 80 degrees and the melting point of -139 degrees. Whereas
the 2 – chlorobutane has boiling point of 69 degrees and a melting point of -123 degrees this shows
that 1 – chlorobutane has a high boiling point and melting point than 2 – chlorobutane because the
intermolecular force is much greater than 2 – chlorobutane so therefore more energy is required to
overcome to break the bonds. 1 – chlorobutane is soluble in water but it is soluble in alcohol and
ether whereas 2 – chlorobutane is slightly soluble to water. Both isomers are clear and colourless
liquid, both isomers are flammable and when it is heated up it can produce toxic fumes. 1 –
chlorobutane has slightly different density than 2 – chlorobutane with the density of 0.886g/cm and
2 – chlorobutane has the density of 0.873g/cm.
Functional group:
It is known that structural isomers belong to separate chemical families (different homologous
series) due to the different functional groups in their structures. An aldehyde or ketone can be
represented by the molecular formula C3H6O.
The first image is propanone, and the second image is propanal. They both have a functional group
like the oxygen and hydrogen. The first image shows that the functional group is located in between
the first and second carbon whereas the second image show that the functional group is located
next to the first carbon. They both have the same chemical formula but the arrangement of atoms
like the functional group are placed different which gives them different chemical and physical
properties.
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,Mohammed Salam Unit 14: LA C
Difference in properties:
Both propanone and propanal are colourless liquid with a pungent, fruity odour and sweetish taste.
The melting point of propanone is -94.9 degrees and boiling point of propanone is 56.08 degrees
whereas propanal is -81 degrees for melting point and 47.9 degrees, propanone has a higher boiling
point than propanal because the intermolecular force is greater than propanal so therefore more
energy is required to break the bonds of propanone. Propanal density is slightly more than
propanone with the density of 0.7970 g/cm3 whereas propanone has the density of 0.7845g/cm3.
Propanone has a higher solubility of water than propanal.
What is stereoisomerism?
The relationship between two or more isomers with the same structure (the same atom linkages)
but different configurations (spatial arrangements), as opposed to constitutional isomerism, in which
the isomers have different structures. Enantiomers, which have molecules that are mirror images of
each other, and diastereoisomers, which do not, are the two types of stereoisomers. There are two
distinct types of stereoisomers that exists in chemistry which are geometric and optical.
Geometric:
Stereoisomerism manifests itself as geometric isomerism, also known as cis-trans isomerism or E-Z
isomerism.
These are E-Z isomers they both have the same chemical formula but the atoms in the arrangement
of space are different which gives them different physical and chemical properties. The first one is E
– 1- 2 Dichloroethane and the second one is Z – 1 – 2 Dichloroethane. The two chlorine from the
second picture faces each other whereas the first image shows that the two chlorine atoms are
facing away from each other.
Difference in properties:
E – 1-2 dichloroethane has a melting point of – 80.0 degrees and boiling point of 60.2 degrees
whereas the Z – 1-2 dichloroethane has a melting point of -49.8 degrees and boiling point of 47.2
degrees, E – 1-2 dichloroethane has a higher boiling point than Z – 1-2 dichloroethane because the
force of attraction is greater than z – 1-2 dichloroethane so therefore more energy is required to
overcome the bonds.
Oleic acid:
(Wikipedia Contributors, 2019)
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, Mohammed Salam Unit 14: LA C
An oleic acid is an omega-9 monounsaturated fatty acid that can be found in many fruits, vegetables,
meats, and oils. Oils with oleic acid can be used as excipients in medications and as emulsifying
components for aerosols. In nature, triglycerides, phospholipids, cholesterol esters, and wax esters
are all found in oleic acids. About 70% of olive oil contains triglycerides and oleic acid. Oleic acid
offers a wide range of applications and advantages. It is most typically used to reduce cholesterol
and prevent heart disease. Additional applications of oleic acid include lowering blood pressure,
increasing fat burning, preventing type 2 diabetes, improving brain function, and slowing cancer
progression.
Elaidic acid:
(Tuscany Diet, n.d)
Elaidic acid has a chemical formula of C18H3402 it is a fatty acid and has a double bond between the
9th carbon and 10th carbon. Elaidic acid is the trans isomer of oleic acid, which means that it is an
unsaturated trans fatty acid. Other processed foods, such as hydrogenated vegetable oils,
margarine, partially hydrogenated soybean oil, and hydrogenated vegetable oils contain trace levels
of this compound.
Difference in properties:
Both have the same chemical formula but the arrangement of atoms in space are structured
differently. The primary distinction between oleic acid and elaidic acid is that oleic acid is a liquid,
whereas elaidic acid is a solid. Additionally, oleic acid is the cis isomer of elaidic acid. Elaidates are
salts and esters of elaidic acid, while olates are salts and esters of oleic acid. Fewer interactions and
lower melting point occurs in oleic acid because of the bend hydrocarbon chain which prevents its
carbon chains from packing tight as together. In comparison with oleic acid, eladic acid has a higher
melting point because its carbon chains provide almost as dense a packing as those found in
saturated stearic acid. The oleic acid has positive effects in the body like it lowers the cholesterol
levels in the body and it improves the heart function whereas the elaidic acid provides negative
effects in the body like it increases in the cholesterol levels in the body and it is responsible for
causing heart problems.
Optical:
Optical isomerism occurs when two substances have the same structural and molecular formulae
but cannot be overlaid on one another. Simply defined, they are mirror images of one another.
These chemicals are known as chiral molecules. The varied forms are referred to as enantiomers.
(Chemagic, 2019)
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