Unit 14A
Functional groups are groups of atoms which give molecules similar properties. There are many
di 昀昀 erent functions groups e.g. ester, alcohol, amines, ketones carboxylic acid. Some have more
than one functional group. Halogens are represented by R or X, they are polar because the halogen
is more electronegative, so it pulls the bonding pair closer. They have van der waal meaning that
the melting point increases with size and they have permanent dipole as they are polar molecules.
Physical properties: non-soluble meaning they don’t dissolve in water.
Halogenoalkanes
The haloalkanes, are a group of chemical compounds made of an alkane with one or more
hydrogens replaced by a halogen atom. They are said to be polar because haloalkanes show
reactivity with nucleophiles due to their polar nature. In these molecules, the carbon atom
connected to the halogen carries a slight positive charge, while the halogen itself is slightly
negative. This polarity creates an electron-de 昀椀 cient carbon atom, which acts as an electrophile
and is consequently attractive to nucleophiles. They are soluble in water because of their polarity.
Reactions of Halogenoalkanes
1. Elimination reaction
An elimination reaction is a type of organic reaction in which two substitute states are removed
from a molecule in either one or two step mechanism.
During an elimination reaction, the OH acts like a base and takes away a hydrogen atom from a
halogenoalkane. The hydrogen becomes positively charged because it leaves without its electron
pair. Then, the positively charged hydrogen ion combines with the OH- nucleophile to form water
(H2O). At the same time, the carbon forms a double bond with the adjacent carbon, and the
halogen attached to that carbon takes a pair of electrons with it. This whole process results in the
formation of an alkene and a bromide ion.
In this chemical equation above it shows a reaction between bromopropane and OH to form
propene. The OH acts like a nucleophile and removes a hydrogen from the halogenoalkane. The
hydrogen becomes positively charged because it leaves with its electron pair. The hydrogen and the
OH come together to form a H2O molecule. The carbon the forms a double bond with the carbon
next to it from the lone pair of electrons left behind by the carbon. Because there are too many
bonds attached to the carbon, the bromine attached the the carbon leaves taking the pair of
electrons with it. This process forms the alkene propene.
, 2. Nucleophilic substitution
The substitution reaction is de 昀椀 ned as a reaction in which the functional group of one chemical
compound is substituted by another group or it is a reaction which involves the replacement of one
atom or a molecule of a compound with another atom or molecule.
In the reaction we can see that 2-昀氀 oro butane reacts with OH to form butane-2-ol. We start with 2-
Floro butane. The Florine in the bond leaves with the pair of electrons. A nucleophile (OH) bonds
with the partially positive carbon to form butane-2-ol.
Commercial importantance:
Halogenalkanes are said to be polar because halogens are more electronegative and attracts and
pulls the electron closer, this nature makes them reactive because they are electronegative the
halogen can leave with the bonding pair. Halogenoalkanes are more reactive then alkanes because
of the presents of an electro negative leaving group. This makes the, useful because they can be
changes easily and can be used to make things like alcohols, nitrates and alkanes. Haloalkanes are
widely used commercially. They are used as 昀氀 ame retardants, 昀椀 re extinguishants, refrigerants,
propellants, solvents, and pharmaceuticals. Subsequent to the widespread use in commerce, many
halocarbons have also been shown to be serious pollutants and toxins.
Alcohols
An Alcohol is any of a class of organic compounds characterised by one or more hydroxyl (―OH)
groups attached to a carbon atom of an alkyl group (hydrocarbon chain). They are soluble in water
because alcohols form hydrogen bonds with water.
Primary alcohols are those alcohols where the carbon atom of the hydroxyl group (OH) is attached
to only one single alkyl group.
Secondary alcohols are those where the carbon atom of the hydroxyl group is attached to two alkyl
groups on either side.
,Tertiary alcohols feature a hydroxyl group attached to the carbon atom, which is connected to 3-
alkyl groups.
Alcohols are polar, since they have oxygen-hydrogen bonds. They also have hydrogen bonds
because the molecule has oxygen and hydrogen bonded together. It also has van der waal as all
molecules do, van der waal increases with size therefore as the size of the molecule increases van
der waal increases and so does the boiling point. This makes alcohols have quite a high boiling
point.
Conditions:
- Re 昀氀 uxing
- Oxidising agent
In the equation we can see that primary alcohols go through two rounds of oxidation during the 1st
oxidation of a primary alcohol 2 hydrogen atoms are removed from the ethanol molecule. One of
the hydrogen leaves without the pair of electrons. The carbon now has an extra pair of electrons. It
then uses this to form a double bond with the oxygen on the molecule. This results in ethanal being
formed. During the second round of oxidisation, oxygen is added to the hydrogen attached to the
carbonyl group to make ethanoic acid.
,Conditions:
- Oxidising agent
- Alcohol must be in excess
- Re 昀氀 uxed gently
- Distilled immediately
We can see that secondary alcohols only go through one round of oxidation. This is because there
is not enough hydrogen to form a second round of oxidation. In the reaction we can see that
propan-2-ol goes through the 昀椀 rst oxidation and two hydrogen atoms are removed and combines
with oxygen to form water. Oxidising a secondary alcohol produces a ketone. In the reaction above
propanone is formed.
Tertiary alcohols (R3COH) are resistant to oxidation because the carbon atom that carries the OH
group does not have a hydrogen atom attached but is instead bonded to other carbon atoms. The
oxidation reactions we have described involve the formation of a carbon-to-oxygen double bond.
Commercial importance of alcohols
These substances have a polar nature, making them great at dissolving organic compounds that
don't mix well with water. They're commonly used in perfumes and cosmetics, adding that extra
touch of allure. In industry, they're super helpful for creating aldehydes and carboxylic acids
through some really cool chemical reactions. Ethanol is a star when it comes to being an industrial
solvent, used for paints, lacquers, dyes, varnishes, costumes, and perfumes. They're also used to
make other organic compounds like ether, chloroform, and iodoform. Methanol is a real MVP as a
chemical feedstock, playing a big role in making plastics, paints, explosives, textiles, and cosmetics.
It even works as an antifreeze for car radiators.
Aldehydes
Aldehyde, any of a class of organic compounds in which a carbon atom shares a double bond with
an oxygen atom, a single bond with at least one hydrogen atom, and a single bond with another
atom or group of atoms.
The reason aldehydes have higher boiling points than hydrocarbons and ethers of similar molar
masses is because of the polar carbonyl groups they have. These groups allow for intermolecular
attractions. As for solubility in water, aldehydes with fewer carbon atoms can dissolve due to the
formation of hydrogen bonds with water molecules. However, as the carbon chain length
increases, their solubility in water decreases. The reactivity of aldehydes is also in 昀氀 uenced by the
polar nature of the carbonyl group.
Conditions:
- Heat under re 昀氀 ux
- BH4- ion
,In this equation the aldehyde becomes reduced and becomes an alcohol. It becomes reduced
because two hydrogens were added. The oxygen has a double bond which is used for one of the
hydrogens to bond to the central carbon. The other hydrogen bond to the oxygen to make a
primary alcohol. This forms propan-1-ol.
When we talk about aldehydes, like RCHO, they can undergo oxidation to form carboxylic acids,
which are represented as RCO2H. However, ketones are not oxidised under these conditions
because they don't have the necessary hydrogen (H) for the elimination process to happen. The key
player in this oxidation reaction is the hydrate that forms when the aldehyde reacts with water.
Conditions:
- Warm the aldehyde with acidi 昀椀 ed dichromate (VI)
In the reaction we can see that propanol gets oxidised. An oxygen atom gets added to the end
chain hydrogen to make propanoic acid.
This special reaction is a nucleophilic addition, where the nucleophilic CN- attacks the electrophilic
carbonyl carbon on the aldehyde, following a protonation by HCN, thereby the cyanide anion being
regenerated. This reaction is also reversible. The CN group in this case is a nucleophile because it
has a pair of electrons and is attracted to the positive end of the aldehyde. When CN approaches
the carbon atom in ethanal, the pair of electrons between carbon and oxygen shifts to oxygen,
giving it a negative charge. Then, when a is added, a positive hydrogen ion is formed. The oxygen,
with its extra electrons, donates a lone pair to the hydrogen ion, resulting in the formation of
2-hydroxypropanenitrile.
Conditions:
- KCN
- H2SO4
- 20°
Commercial importance
,Smaller aldehydes are polar molecules and can form dipole-dipole forces in addition to dispersion
forces. Unlike alcohols, aldehydes and ketones generally have weaker intermolecular forces because
they can't make hydrogen bonds like alcohol molecules can. Benzaldehyde, which is an aldehyde, is
a key ingredient in making perfumes, cosmetics, and dyes. It's also used to give a delicious almond
昀氀 avor to various food products and even acts as a bee repellant.
Ketones
A ketone is a type of organic compound that has a special group called a carbonyl group. This
group consists of a carbon atom bonded to an oxygen atom. So, ketones can form weak hydrogen
bonds with water through the oxygen atom in the carbonyl group. When the carbon chain in a
ketone is shorter (3 carbons or fewer), it is soluble in water. But as the carbon chain gets longer,
its solubility in water decreases. Ketones can also form hydrogen bonds with other ketone
molecules, which
a 昀 昀 ects their boiling points. Unlike alkanes, aldehydes and ketones are polar because of the
oxygen atom. This makes the dipole-dipole interactions stronger than the dispersion forces in
alkanes. As a result, the boiling points of ketones are in between those of alkanes and alcohols.
An electron transfer between two species is involved in a chemical reaction called a redox reaction.
In an addition-reduction reaction, the oxidation number of a molecule, atom, or ion change as it
gains or loses an electron. Reduction of a ketone leads to a secondary alcohol. A secondary alcohol
is one which has two alkyl groups attached to the carbon with the -OH group on it. We can see in
the reaction that 2 hydrogens are added onto butan-2-ol. The double bond with oxygen and carbon
becomes a single bond and the other bond is used to bond a hydrogen to the same carbon. The
other hydrogen bonds to the oxygen to make the -OH group which makes this an alcohol.
Conditions:
, - NaBH4 in water with methanol
A nucleophilic addition reaction is basically when a nucleophile, which is a molecule with a pair of
electrons to share, forms a strong bond with a molecule that is lacking electrons. These reactions
are super important in organic chemistry because they allow us to transform carbonyl groups into
di 昀昀 erent functional groups. It's like a cool way to change one type of molecule into something
completely new and useful.
When a nucleophile comes into contact with the carbonyl carbon of an aldehyde or ketone, there
isn't a leaving group involved. Instead, the nucleophile "pushes" the electrons in the pi bond up
towards the oxygen. Once the carbonyl has reacted with the nucleophile, the oxygen, which now
carries a negative charge, can also act as a nucleophile itself. It's like a chain reaction where one
molecule sets o 昀昀 a series of reactions.
in this case, CN acts as a nucleophile because it has a pair of electrons and is attracted to the
positive end of the ketone. When CN approaches the carbon atom in butanone, the pair of
electrons between carbon and oxygen shifts to oxygen, giving it a negative charge. Then, when an
acid is added, a positive hydrogen ion is formed. The oxygen, with its extra electrons, donates a
lone pair to the hydrogen ion, resulting in the formation of 2-hydroxy propanenitrile.
Conditions:
- KCN
- H2SO4
- 20°C
Commercial importance:
Smaller ketones are polar molecules and can form dipole-dipole forces in addition to dispersion
forces. Unlike alcohols, aldehydes and ketones generally have weaker intermolecular forces
because they can't make hydrogen bonds like alcohol molecules can. They are most widely used as
solvents, especially in industries manufacturing explosives, lacquers, paints, and textiles. Ketones
are also used in tanning, as preservatives, and in hydraulic 昀氀 uids.
Carboxylic Acids
Carboxylic acid, any of a class of organic compound in which a carbon atom is bonded to an oxygen
atom by a double bond and to a hydroxyl group(―OH) by a single bond. A fourth bond links the
carbon atom to a hydrogen atom or to some other univalent combining group.
The solubility of compounds containing the carboxyl functional group in water depends on the size
of the compound because carboxylic acids have van der waal, permanent dipole and hydrogen
, bonds the hydrogen bonds and permanent dipole are the reason carboxylic acid is soluble in water
because water also has the same intermolecular forces. The smaller the compound (the shorter
the R group), the higher the solubility. The boiling point of a carboxylic acid is generally higher
than that of water. When carboxylic acids react with metals that are more reactive, they produce
a salt and hydrogen gas. The reactions are similar to what happens with acids like hydrochloric
acid, but they usually happen at a slower pace. For instance, when we have dilute ethanoic acid
and magnesium, they can react together.
In this reaction propanoic acid reacting with a metal (sodium). We can see that the hydrogen
bonded the oxygen in the propanoic acid leaves the bond leaving a space for the sodium to bond
with the oxygen to form sodium oxide. This makes sodium propanate and hydrogen.
When acids react with carbonates like calcium carbonate found in chalk, limestone, and marble,
they produce a salt, water, and carbon dioxide. The carbon dioxide creates bubbles during the
reaction, which we can see as 昀椀 zzing. When carboxylic acids react with metal carbonates, they
create a metal salt, carbon dioxide gas, and water. However, compared to stronger acids like
hydrochloric or sulphuric acid, this reaction tends to be a bit slower.
In the chemical equation propanoic acid reacts with sodium carbonate and gives us the product of
sodium propanate, water and carbon dioxide. We can see that the hydrogen bonded the oxygen
in the propanoic acid leaves the bond leaving a space for the sodium to bond with the oxygen to
form sodium oxide. This makes sodium propanate, water and carbon dioxide.
Commercial importance:
In a pure carboxylic acid, hydrogen bonding can occur between two molecules of acid to produce a
dimer. This immediately doubles the size of the molecule and so increases the van der Waals
dispersion forces between one of these dimers and its neighbors - resulting in a high boiling point.
They re useful s we can make many di 昀昀 erent things from them eg Esters. Carboxylic acids and
their derivatives are used in the production of polymers, biopolymers, coatings, adhesives, and
pharmaceutical drugs. They also can be used as solvents, food additives, antimicrobials, and
昀氀 avorings.
Esters
In chemistry an ester is a compound derived from an acid in which the hydrogen atom of at least
one acidic hydroxyl group (−OH) of that acid is replaced by an organyl group (−R).
They have a pleasant smell. Esters with higher acids are colourless solid compounds. Esters are
soluble in water in normal conditions. Esters are highly volatile and are highly 昀氀 ammable.
