Organic Chemistry

Organic chemistry

The study if carbon compounds like CO2, CO, CO32-, HCO3-

Formulae of organic compounds

Empirical

Empirical formula gives the simplest ratio of the number of atoms of each element present in each compound

Molecular

Molecular formula gives the actual number of atoms of each element present in the compound

Structural

Structural formula shows the order of the atoms joined together in an organic compound. These formulas are usually written in one line

EX: Ethane- CH3CH3

Ethene- CH2=CH2

Ethanoic acid- CH3C00H

Displayed

Displayed formula shows the order of the atoms joined together, as well as the orientation of the atom and bond angles

Skeletal

Skeletal formula shows only the functional groups and the carbon and hydrogen are hidden.

There is a carbon atom at each junction and at the end of the bond, there is no carbon atom at a place occupied by another functional group
There is enough hydrogen atoms bonded to each carbon so that each carbon has only four bonds

Functional groups

Alkene

an alkene is a hydrocarbon that contains a carbon–carbon double bond

Alkyne

an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond

Halogenoalkanes

Halogenoalkanes are alkanes who have had one or more hydrogen atoms replaced by halogens.

Alcohol

Alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a saturated carbon atom

Ether

Ether, any of a class of organic compounds characterized by an oxygen atom bonded to two alkyl or aryl groups

Aldehyde

an aldehyde is a compound containing a functional group with the structure −CHO, consisting of a carbonyl center (a carbon double-bonded to oxygen) with the carbon atom also bonded to hydrogen and to any generic alkyl or side chain R group

Ketone

a ketone is a functional group with the structure R₂C=O, where R can be a variety of carbon-containing substituents

Carboxylic acid

A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group

Ester

An ester is a chemical compound derived from an acid in which at least one –OH hydroxyl group is replaced by an –O– alkyl group

Nitrile

A nitrile is any organic compound that has a −C≡N functional group

Amine

The functional group of this group are amines. At the end of a carbon chain, the carbon atom is bonded to a nitrogen atom, which is bonded to two other hydrogen atoms.

Amide

The functional group of this group are amides. It is similar to an amine, but at the carbon atom at the end where it is bonded with a nitrogen atom, the two other bonds of the carbon atom are used in a double bond with an oxygen atom instead of two hydrogen atoms.

Carbocations

Carbocations are organic compounds that have lost an electron and are grouped into primary, secondary and tertiary carbocations. They consist of a carbon atoms that are bonded to either a hydrogen atom or a alkyl group. Primary carbocations have the 'main' carbon atom bonded to one alkyl group and 2 hydrogen atoms. The remaining bond is for the missing electron. Secondary carbocations have 2 alkyl groups and 1 hydrogen. Tertiary carbocations have 3 alkyl groups.

Alkyl groups have the property of repelling electrons, so as it goes from primary to tertiary carbocations, the electrons get more spread out from the different alkyl groups. The charge density decreases and the molecule becomes more energetically stable.

Names of organic compounds

The front section of the name is decided by the length of the longest carbon chain in the compound. Carbon is used because all organic compounds must have carbon in them, and they usually form chains of carbon with other elements connected to the sides of the carbon chain. Since carbon is the main part of the compound, it is used for the front part of the name

The back section of the name is decided by the functional group of the compound. The functional group is the identifier of what kind of compound it is, so that's why it is used.

Front Section

The total amount of carbon atoms present is not used, so that side branches of carbon are not counted. The list of names is shown below:

1: meth-
2: eth-
3: prop-
4: but-
5: pent-
6: hex-
7: hept
8: oct-
9: non-
10: dec-

Back Section

The list of names for the different functional groups are shown below:

alkane: -ane
alkene: -ene
alcohol: -anol
carboxylic acid: -anoic acid
halogenalkane: chloro / floro / bromo-
aldehyde: -al / -anal
ketone: -one / -anone
ester: -oate / anoate
amide: -amide / -anamide

Branches

If a carbon chain has a side branch, neither the front nor the back part are used to indicate that the compound has a side branch. Instead, it is put in front of the 'main' part of the name. For example, there is an alcohol with four carbon atoms in the main chain. It has a branch with 2 carbon atoms attached to the second carbon atom. Then, it will be named 2 - ethylbutanol. The name of the branch also follows the normal rule for the front part, but the back part of the branch name will be -yl.

Positions

If a compound has a functional group that can be attached to any carbon atom, we can indicate exactly where it is by putting it in the name.

For example, there is an alcohol with four carbon atoms and the -OH is attached to the third carbon from the right. Its name is butanol, but we can indicate where the -OH is by calling it buta-2-nol. Why 2? This is because although it is attached to the 3rd carbon atom from the right, it can be counted as attached to the 2nd carbon atom from the left. It is the same position, but the number is different. When this happens, we can choose the smaller number.

Steps can be called FLOP

F= Functional group

LO= Longest carbon chain

P= Parts and position

Use FLOP to name the system respectively

Organic reactions

Organic reactions are classified by two ways:

by the type of reagent use

-Nucleophilic

-Electrophilic

By what happens during the reaction

-Addition

-Substitution

-Elimination

common reactions:

Free-radical substitution
Electrophilic substitution
Nucleophilic substitution
Electrophilic addition
Nucleophilic addition
oxidation
reduction
hydrolysis

Free-radical substitution

Free-radical substitution consists of 3 phases: Initiation, propagation and termination

During initiation, the molecule that will substitute the hydrogen atoms in the alkane will undergo homolytic fission. For example, a chlorine (Cl₂) atom will be broken down into 2 free radical chlorine ions.

During propagation, one free radical molecule and one molecule will react, and another free radical will form. This will continue until there are no more reactants or the reaction is finished. For example, CH₄ which is normal will react to free radical chlorine Cl⁻ ion, and the products are CH₃⁻ and HCl. Next is CH₃⁻ + Cl₂ -> CH₃Cl + Cl⁻ . Then, CH₃Cl + Cl⁻ -> CH₂Cl⁻ + HCl. And the cycle continues until all the H atoms are replaced, the Cl atoms run out, or the reaction is stopped.

During termination, the free radical molecules will join back with each other again and the molecules will all be normal. No more reactions will proceed. For example, Cl⁻ +Cl⁻ -> Cl₂.

Hydrolysis

Hydrolysis is a chemical process in which a molecule of water is added to a substance and broken down into simpler molecules. The OH ion will replace any an atom that is not C or H . For example, C2H5Br + H2O = C2H5OH + HBr

Oxidation

Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. Oxidation occurs when the oxidation state of a molecule, atom or ion is increased. The opposite process is called reduction, which occurs when there is a gain of electrons or the oxidation state of an atom, molecule, or ion decreases

Alkenes will form different products when oxidized depending on the different compounds bonded to each carbon atom at the double bond, as well as the reaction conditions. It will be different when the oxidizing agent (Potassium(VII) manganate) is cold and dilute, or hot and concentrated.

When the oxidizing agent is cold and dilute, the double bond will simple be broken and an OH ion will be attached to each carbon atom, forming a diol.

When the oxidizing agent is hot and concentrated, it will depend on the different compounds bonded to each carbon atom. When the carbon atom is bonded to 2 hydrogen, it will form carbon dioxide and water. When the carbon atom is bonded to 1 hydrogen and 1 R group, it will form a carboxylic acid. When the carbon atom is bonded to 2 R groups, it will form a ketone. The two carbon atoms from the double bond will form separate products.

Reduction

Reduction involves a half-reaction in which a chemical species decreases its oxidation number, usually by gaining electrons

Elimination

Any of a class of organic chemical reactions in which a pair of atoms or groups of atoms are removed from a molecule, usually through the action of acids, bases, or metals and, in some cases, by heating to a high temperature.

Covalent bond breaking

Heterolytic fission

Heterolytic fission, also known as heterolysis, is a type of bond fission in which a covalent bond between two chemical species is broken in an unequal manner, resulting in the bond pair of electrons being retained by one of the chemical species

A nucleophile is an atom or a molecule that has received the pair of electrons from the heterolytic fission, or from somewhere else. The nucleophile is very reactive as it will try to give away its lone pair of electrons. They are negatively charged and will be attracted to positive charges.

An electrophile is an atom or a molecule that lacks electrons and can accept electrons. The electrophile is very reactive as it will try to receive electrons. It is positively charged and will be attracted to negative charges.

Homolytic fission

Homolytic fission is a type of bond fission that involves the dissociation of a given molecule wherein one electron is retained by each of the original fragments of the molecule.

Isomerism

Isomers are two or more compounds with the same molecular formula but a different arrangement of atoms in space. Organic molecules which exhibits this property show isomerism

This excludes any different arrangements which are simply due to the molecule rotating as a whole, rotating about particular bonds.

Two types of isomerism

Structural

Chain isomerism
Positional isomerism
Functional isomerism

stereoisomerism

Geometrical (cis-trans) isomerism
Optical isomerism

Difference

Structural

Structural isomers have the same molecular formula but different structural formula
Arises from the different ways in which atoms can join together to form molecules
The atoms are linked in different sequences and in different ways

Stereoisomerism,2^n

Stereoisomerism have the same molecular and structural formula but different arrangements of their atoms in space
Arises from the different ways in which the various groups in the molecule can arrange in space
The atoms are linked in the same sequence and in the same way but differ in their arrangement in space

Chain isomerism

Chain isomerism arises due to the different arrangement of carbon atoms in a chain. The carbon atoms may be arranged in a straight chain or branched chain

Positional isomerism

Positional isomerism arises due to different positions of functional group in the carbon chain

Functional isomerism

Functional isomerism arises due to different functional groups

Note: Propanal is an aldehyde while propane is a ketone, they belong to different homologous series

Geometrical(cis-trans) isomerism,

Cis-trans isomerism arises due to the rotation about a bond is restricted. It is common in compounds containing carbon-carbon double bond(C=C) and certain ring systems
A C=C bond cannot be rotated due to the presence of π. A π bond will break if a rotation occurs. Conversely, a carbon-carbon single bond is rotatable.
In ring systems, rotation about a bond is restricted due to the linkage of the ring because the C-C bond is now part of the ring system
Geometrical isomers occur in pairs, differing from each other in the positioning of the two groups across the double bond.

-A cis-isomer has two groups on the same side of the double bond

-A trans-isomer has the two groups on the opposite sides of the double bond

Geometrical isomers cannot exist if either carbon carries identical groups. In short to have geometrical isomers, it is essential to have two different groups on the left and two different groups on the right.
Geometrical isomers have similar chemical properties but different physical properties
Cis-isomer has higher boiling point than trans-isomer because dipoles in cis-isomer do not cancel each other, causing the entire molecule to have a net dipole moment and it is polar. Permanent dipole-dipole forces exist and more energy is required to overcome it
Trans-isomer generally has a higher melting point than cis-isomer This is because in the solid state, trans-isomer pack more efficiently in the crystalline lattice due to its shape

optical isomerism

Optical isomerism arises due to the ability of compounds to rotate the plane of polarisation of a plane - polarised light
For a compound to be optically active:

-It needs to have an asymmetrical carbon with four different groups attached to it so that there is no plane of symmetry. The carbon atoms with four different groups attached to it is called the chiral carbon or chiral centre.

-The isomer must be mirror-images of each other and are non-superimposable. That is, no matter how the molecules are rotated, they never fully resemble each other

How to identify optical isomers

In chain systems, check which carbon has four different groups attached to it
In ring systems, check also which carbon has four different groups attached to it. A different group can be identified by tracking around that ring from a particular carbon atom in either clockwise or anti-clockwise direction. If the pattern along the way is the same, that carbon atom is not chiral, and the converse is also true

Only carbon 9(with two CH3) is not a chiral carbon in this cholesterol molecule

Cycloalkanes

Cycloalkanes are alkanes with carbon atoms attached in the form of a closed ring. functional groups: An atom or groups of atoms that substitute for a hydrogen atom in an organic compound, giving the compound unique chemical properties and determining its reactivity.