Functional group chemistry for designer molecules
Involving the examination and enquiry into the configuration, determinants and reactions
of compounds that are comprised of carbon atoms, Organic Chemistry is a branch of
science utilised to analyse the properties of existing substances with two or more
elements chemically joined together.
Correspondingly, functional groups play a consequential role in the characteristics that
the molecules will attain. Identified as specified substituents of atoms present in a
molecule (https://en.wikipedia.org/) functional groups aid in the determination of
predictable reactions that may transpire, as well as the chemical properties of a
particular substance.
Additionally, they can be utilised in the naming of organic compounds via conjoining the
parent alkanes and functional groups to formulate a systemic nomenclature.
Bound together through the means of covalent bonds,
(https://courses.lumenlearning.com/) the:
a. Alpha Carbon – First carbon atom attached to the functional group
b. Beta Carbon – Second carbon atom attached to the functional group
c. Gamma Carbon – Third carbon atom attached to the functional group
The functional groups can be categorised into three groups:
a. Primary
b. Secondary
c. Tertiary
Halogenoalkanes
Recognised as alkenes where the hydrogen atoms in their structure have been replaced
by one or more halogen atoms, Halogenoalkanes can be classified into three fractions:
Primary Halogenoalkane (1oC)
This consists of the carbon joined to a halogen also connected to one alkyl group.
Figure 1 – An Illustration depicting Primary Halogenoalkanes
Bromoethane, 1-chloropropane, 1-iodo-2-methlypropane
Secondary Halogenoalkanes (2oC)
This consists of the halogen attached to the carbon. The halogen will be directly
linked to two alkyl groups.
Figure 2 – An Illustration depicting Secondary Halogenoalkanes
2-bromopropane, 2-chlorobutane
Tertiary Halogenoalkanes (3oC)
This consists of the halogen attached to the carbon being directly linked to three
alkyl groups.
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, Figure 3 – An Illustration depicting Tertiary Halogenoalkanes
2-bromo-2-methylpropane, 2-chloro-2-methlypropane
Halogenoalkanes can be formed through two processes
a. Through a chemical reaction of hydrogen halides and alkenes
b. Through replacing the -OH function group of an alcohol with a halogen atom.
Elimination Reactions of Halogenoalkanes
Recognised as the separation of a small group of atoms from a substantial molecule,
Halogenoalkanes can carry out elimination reactions with the inclusion of potassium and
sodium hydroxide and heat, in the form of refluxing. Refluxing enables the solution to be
heated in a controlled fashion, inhibiting the loss of reactants by collecting the vapours in
a condenser.
Figure 4 – An Illustration depicting Elimination Reaction with 2-bromobutane
Figure 5 – An Illustration depicting Elimination Reaction Mechanism with 2-bromobutane
In this chemical reaction, a halogenoalkane reacts with sodium hydroxide (NaOH). As
displayed in figure 5, a hydrogen ion will be removed from the carbon in 2-bromobutane
by the sodium hydroxide, as it is acting as a base. This enables an electron pair to
compose a double bond between the carbon atoms.
As a result, the Bromide atom (Br) will be removed, remaining as a Br __. The Bromide is
the leaving group. The products formulated will be water, but-1-ene (CH 2=CHCH2CH3),
and bromine.
Nucleophilic Substitution of Halogenoalkanes
Recognised as a reaction between a positively charged electrophile and a nucleophile
resulting in the leaving group being replaced with an electron rich compound, in
nucleophilic substitution, the halogen atom will be replaced with an -OH group forming
an alcohol. This is done through refluxing. Conditions include heat, sodium hydroxide and
an ethanolic solvent
Figure 6 – An Illustration depicting Nucleophilic Reaction with 2-bromobutane to make a alkene-propene
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, Figure 7:8 – An Illustration depicting Nucleophilic Reaction Mechanism with 2-bromobutane
The halogen is electronegative, attracting electrons to its structure giving it a delta
negative charge. As the carbon atom has a delta positive charge it will attract the lone
pair electrons, resulting in the breaking of the halogen-carbon bond causing the
formulation of a Bromide (Br__) ion.
When refluxing the 1-Bromo-1,1-dimethylethane with a solution of ethanol, water and
sodium hydroxide, the -OH replaces the halogen producing an alcohol, tert-butanol.
Properties of Halogenoalkanes
Figure 9 – An Illustration depicting the Boiling Points of Halogenoalkanes
As displayed in figure 9, the boiling points of halogenoalkanes will increase as you go
down the group in correspondence to the lengthening of the chain
(Chloride<Bromides<Iodides). This is because they will have more electrons and
therefore more Vander Waal forces, requiring more (heat) energy to break them apart,
increasing their boiling points.
Halogenoalkanes are slightly soluble in water, as when they dissolve in water the dipole-
dipole and Vander Waal forces are broken in the halogenoalkanes as well as the
hydrogen bonds in the water. Between the molecules of water and halogenoalkanes,
there will only be dipole-dipole and Vander Waal.
Both forces are not as strong as the hydrogen bonds, therefore little energy will be
utilised when separating the water molecules. Therefore, halogenoalkanes will be less
soluble in water.
They are more likely to dissolve in organic solvents as they usually have similar
intermolecular forces of attraction (Vander Waal and dipole-dipole).
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, Tertiary halogenoalkanes are more reactive in water as they have the highest polarity,
while secondary and primary halogenoalkanes are slower.
Figure 10 – An Illustration depicting the Reactivity of Halogenoalkanes
In accordance to the graph shown in figure 10, the least reactive to the most reactive is
fluoroalkanes<chloroalkanes<Bromoalkenes<Iodoalkanes. This is because fluorine has
the highest electronegativity, while the carbon molecule and iodine are equal in their
electronegativity, so there’s no separation in their bond.
Whereas alkyl bromides and iodides tend to be heavier than water, alkyl fluorides and
iodides will be much lighter. The trend noticed is that as the group increases, so does the
density.
Due to their properties, Halogenoalkanes can be used as:
a. Solvents
b. Propellants
c. Refrigerants
d. Flame Retardants
e. Fire Extinguishers
This is mainly because they are non-flammable and not really toxic.
Alcohols
Established as an organic compound, alcohols can be identified by its hydroxyl functional
group (−OH) that is attached to a saturated carbon atom (https://en.wikipedia.org).
Furthermore, utilising positional isomerism, alcohols can be identified depending on the
location of the functional group in the carbon chain. This is also used to organise Alcohols
into three classes:
Primary Alcohols (1oC)
This consists of the carbon that carries atom carrying the -OH functional group
that is attached to an alkyl group.
Figure 11 – An Illustration depicting Primary Alcohols
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