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UNIT 14: APPLICATIONS OF ORGANIC CHEMISTRYA. Chemists design designer molecules by using functional groups.
Carbonyl groups are chemically organic functional groups containing a double bond between carbon
atoms and oxygen atoms --> [C=O]. Having an uneven electron distribution makes this double bond
polar. Oxygen has a very electronegative charge, which means that electrons are drawn to it. A
positive charge on carbon attracts nucleophiles, which is why it will attract nucleophiles. It occurs
when there is an electron deficiency in a region. Aldehyde, ketone, carboxylic acid, ester, oxyl
chloride, and amine products are all products of carbonyl reactions. Reactions between carbonyl
groups are more volatile than reactions between non-carbonyl groups. The bond is appealing to
nucleophiles because of the lack of C=O bonds in the compounds. An example would be haloalkanes,
C-X bonds attract nucleophiles due to their electron-deficient carbon atom. By replacing the halogen
with a nucleophile, a nucleophilic substitution reaction is allowed.
Halogenoalkanes:
An alkane containing more than one hydrogen atom is called a halogenoalkane. The halogens are
either fluorine, chlorine, bromine, or iodine atoms or parts thereof.
Halogenoalkanes different types:
As halogens are positioned on carbon chains, they fall into different classes based on the position of
the halogen atom.
Primary halogenoalkanes:
One other alkyl group is attached to carbon carrying the halogen atom. In alkyl group we can find
methyl or ethyl. A branched carbon chain group is one that contains carbon atoms in chains. The
general symbol for alkyl groups is R.
Secondary halogenoalkanes:
There can be two different or the same alkyl groups attached to the carbon with the halogen.
Tertiary halogenoalkanes:
In this arrangement, three alkyl groups, whether the same or different, are attached directly to the
carbon atom holding the halogen.
Properties of Halogenoalkanes:
There are different types of forces that can vary the boiling point of each halogenoalkane.
Van Der Waals dispersion forces:
Molecules with more electrons and longer lengths are more likely to attract each other. Temporary
dipoles are thus set up that are larger because of this. Carbon chains have a higher boiling point
when there are more carbon atoms in them.
,For a given number of carbon atoms, an increase in boiling point is also a result of an increase in
dispersion forces as you move from a chloride to a bromide to an iodide.
Except for the carbon-iodine bond, all carbon-halogen bonds are polar because the electrons are
attracted to the halogen atom closer than to carbon. Since halogens are more electronegative than
carbon (aside from iodine), they are less stable.
Furthermore, the permanent dipoles will be attracted to one another, thus adding to the dispersion
forces. With less polar bonds (like chloride, bromide and then iodide, for example), the size of those
dipole-dipole attractions will decrease. There is much less importance given to the dipole-dipole
attraction between permanent dipoles as opposed to the temporary dipoles that cause dispersion.
It is almost impossible to notice the loss of permanent dipoles in the molecules due to the great
increase in electrons by the time you reach the iodide.
Boiling points of some isomers
Hence, halogenoalkane boiling points decrease from primary to secondary to tertiary as the isomers
become more complicated.
There has been a fall in dispersion force effectiveness, which is the simple cause of this.
Molecular length determines the magnitude of temporary dipoles. Molecules that lie closely
together also have stronger attractions. There will be little contact between tertiary halogenoalkanes
due to their short and fat natures.
Solubility of Halogenoalkanes:
In water:
There is very little water solubility in the halogenoalkanes. The van der Waals dispersion and dipole-
dipole interactions between molecules of halogenoalkanes must be broken to halogenoalkanes to
dissolve in water. Hydrogen bonds between the molecules of water must also be broken for
halogenoalkanes to dissolve in water. As a result of both, energy costs are involved.
Water molecules and halogenoalkanes generate energy when new attraction is formed. Dispersion
forces and dipoles will be the only forces interacting. Due to the weaker bonds than the hydrogen
bonds, there is less energy released than during the separation of water molecules.
Change is sufficiently unprofitable that there is very little dissolution.
Solubility in organic solvents:
Halogenoalkanes tend to dissolve in organic solvents because the intermolecular interactions
between them are strong.
Chemical reactivity of halogenoalkanes:
Each carbon-halogen bond has a different strength pattern.
,When you go from carbon-fluorine to carbon-iodine, bond strength falls, and carbon-fluorine is
much stronger than other bonds.
The bond between carbon and halogen must be broken in order for anything to react with
halogenoalkanes. In that order, fluoride, chloride, bromide, and iodide are more reactive because
they get easier to react with each other. Reactivity is highest for iodoalkanes and lowest for
fluoroalkanes
Bond polarity:
There is a significant electronegative difference between fluorine and iodine among the four
halogens. The electron pair at the halogen end of the carbon-fluorine bond will be dragged most
towards it because of this.
An example of a simple methyl halide:
It is impossible to separate the charge on the bond between carbon and iodine since their
electronegativities are equal.
There are two types of reaction that can happen in halogenoalkanes which are nucleophilic
substitution and elimination reaction where a sodium or potassium hydroxide solution is added to
the halogenoalkane during both reactions.
During nucleophilic substitution, the carbon-halogen bonds are broken to form positive and negative
ions. Positively charged carbon atoms react with fully or slightly negatively charged particles, thereby
pushing off halogen particles when they come in contact with them.
In this example, we can see a nucleophilic substitution reaction using the hydroxide ions present
may result in an alcohol by replacing the halogen atom with the -OH group.
A conversion of 2-bromopropane produces propan-2-ol.
Elimination
, An alkene - propene, has been produced from 2-bromopropane.
An additional carbon atom has been removed with a hydrogen atom along with the bromine from
the middle carbon atom. All simple elimination reactions involve the formation of a double bond
between adjacent carbon atoms.
It depends on the type of alkane,It may also depend on the temperature and it what surface the
reaction will take place as in for example in water what mainly will happen is substitution whereas in
ethanol, elimination reaction will occur.
Regards the temperature, if it is higher then elimination will occur, same as if the concentration of
Sodium or Potassium hydroxide is purer.
Hydroxide ions
Nucleophilic substitution reaction:
A halogenoalkane is substituted with OH- ions when its nucleophiles are hydroxide ions. The slightly
positive carbon can, for instance, be attacked by one of the oxygen's lone pairs. The -OH group
becomes attached in place of the bromine ion because of this process.
Elimination reaction:
A very strong base is the OH- ion, which is formed when hydrogen ions combine with oxygen ions to
form water. By eliminating the hydroxide ion from the CH3 group, a hydrogen atom is removed.
After a cascade of electron pair movements, a double bond between carbon and carbon is formed
and lost as Br-.
Alcohols:
Carbon atoms directly bonded to the hydroxyl group are organic molecules called alcohols. It is
technically called "carbinol" carbon because it is directly attached to the OH.
There is generally one formula for them, which is CnH2n+1OH.
Primary, Secondary or Tertiary Alcohol type:
If the carbon attached to OH is not present in the alcohol, then it cannot be classified as primary,
secondary, or tertiary. If it contains one carbon, then it will be classified as primary, if two carbons
are attached, then it is secondary and so on. Methanol is created by three hydrogen atoms with zero
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