- Created by: larissa67
- Created on: 26-08-18 06:52
- Within a group of compounds, they all have the same atom or groups of atoms, known as a functional group.
- The functional group in a group of compounds characterises how they behave chemically.
- Alchohol functional group = O-H
- Alkene functional group = C=C double bond
- Alkane functional group = C-C single bond
- Carboxylic acid functional group = -COOH
- Ester functional group = -O- (alkyl group)
1 of 22
Bonding in organic molecules
- There are 2 types of bonding in organic molecules
- 1. Sigma bonding
- 2. Pi bonding
2 of 22
- Single covalent bonds in a compound are known as sigma bonds.
- The pair of electrons in a sigma bond is found between the nuclei of 2 atoms that are sharing the electrons.
- Electrostatic attraction between negative electrons + positive nuclei bonds atoms to eachother.
- Each carbon can form 4 pi bonds in a compound.
- The 4 bonding pairs of electrons around each carbon atom repel eachother.
3 of 22
- The pi bond is made up of double carbon bonds, such as the one in alkenes.
- The carbon atoms involved in a pi bond each form 3 sigma bonds, leaving one carbon atom with a spare outer electron in a 2p orbital.
- When 2 of these 2p orbitals overlap, it forms a pi bond.
- The pi bonds are made up of 2 lobes that lie above and below a plane.
4 of 22
- Structual isomers are compounds with the same molecular formula, but a different structural formulae
- There are 3 types of structural isomerism
- 1. Positional isomerism
- 2. Functional group isomerism
- 3. Chain isomerism
5 of 22
Structural isomerism; position
- In postional isomerism, it is the position of the functional group that changes place in each isomer
- There is free rotation around single C-C bonds, but NOT in double C=C bonds.
6 of 22
Structural isomerism; functional group
- In functional group isomerism, it is the functional group that changes in each isomer.
- For example, for a compound such as C2H8O, we can draw both an alcohol and an ether.
- The two isomers that can be drawn have different functional groups, so therfore have different chemical properties & chemically behave differently.
7 of 22
Structural isomerism; chain
- In chain isomerism, isomers differ in terms of their carbon skeleton and how it is arranged.
8 of 22
- Stereoisomerism is when we have compounds that have the same molecules bonded to eachother but have different arrangements in space.
- There are 2 types of stereoisomerism;
- Cis-trans isomerism
- Optical isomerism
9 of 22
- Arrangements can result in cis-trans isomerism because there is restricted rotation about the double C=C bond
- Cis isomerism means that both of the SAME type of atom are arranged on the same side of the molecule, imagine "cis" = "sis", and sisters stay together
- Trans isomerism means that the same molecules are arranaged so that they are across from eachother, going in a diagonal line, imagine "trans" = "across", so they are diagonal
- Whenever we have compounds with a double C=C bond, they can display cis-trans isomerism
10 of 22
- If a molecule contains a carbon atom that is bonded to 4 different atoms/groups, it can form 2 optical isomers
- The 2 different molecules are mirror images of eachother
- The carbon atom with 4 different groups attached is called the chiral centre of the molecule
- A pair of optical isomers will rotate the plane of polarised light by equal amounts, but in different directions
11 of 22
Organic reactions & mechanisms
- There are 2 ways in which a covelant bond can be broken;
- 1. Homolytic fission
- 2. Heterolytic fission
12 of 22
- Type of bond breaking
- This type of bond breaking is when an electron is taken by each of the atoms from the covalent bond
- The species porduced when a bond breaks homolytically is called a free radical
- All free radicals have an upaired electron and are very reactive
13 of 22
- This type of bond breaking involves the "uneven" breaking of the covalent bond between atoms
- In heterolytic fission, the more electronegative atom takes both of the electrons
14 of 22
- Carbocations are formed when a carbon atom has 3 bonds and one positive charge
- They are an alkyl atoms
- There are 3 types of carbocations
- 1. Primary carbocations (least stable)
- 2. Secondary carboctions
- 3. Tertiary carbocations (most stable)
- The carbocations become more stable when they have more alkyl groups
- Alkyl groups, eg. CH3, C2H5 tend to push electrons away from themselves
- This is called the positive inductive effect of alkyl groups
- This means that the more alkyl groups in a carbocation, the more spread out the chrage density is on the carbocation, so they are more stable
15 of 22
Electrophile & Nucleophiles
- An electrophile is an acceptor of electrons
- A nucleophile is a donator of a pair of electrons
16 of 22
Types of organic reaction
- Addition = involves the formation of a single product from 2 reactanct molecules
- Eg. C2H4 + Br2 = C2H4Br2
- Elimination = the removing of a small molecule from a larger one
- Eg. C2H5OH = C2H4 + H2O
- Substitution = the replacement of one atom by another
- Eg. CH4 + Cl2 = CH3Cl + HCl
- Hydrolysis = breakdown of a molecule using water
- Eg. C2H5Br + H2O = C2H5OH + NaBr
- Oxidation = loss of electrons from a species
- Reduction = gain of electrons from a species
17 of 22
Reactions of the alkanes; combustion
- If an alkane is burnt in an excess of oxygen, it undergoes complete combustion
- The carbon - gets fully oxidised to carbon dioxide
- The hydrogen - gets fully oxidised to water
- Alkane + oxygen = carbon dioxide + water
18 of 22
Reactions of the alkanes; substitution
- Alkanes undergo substitution reactions with halogen in sunlight, but will not take place in darkness (it is explained why later)
- A hydrogen in the alkane molecule gets replaced by a halogen molecule
- Eg. CH4 + Cl2 = CH3Cl + HCl
- There are 3 steps to substitution reactions
19 of 22
- The first step is called the initiation step.
- The bond between the two halogen atoms (we will use chlorine in this example) is broken by UV light from the sun
- Cl2 = 2Cl*
- Here is an example of homolytic fission, both of the chlorine atoms takes an electron from the covalent bond to form a free radical
20 of 22
- Free radicals are very reactive, and will attck the alkanes.
- CH4 + Cl* = CH3 + HCL
- Here, a methyl free radical is produced
- CH4 + Cl* = CH3 + HCL
- This can then attack a chlorine molecule
- *CH3 + Cl2 = CH3Cl + Cl
21 of 22
- When 2 free radicals meet, they will react with eachother
- They only produce 1 single product
- As no more free radicals are made, the chain reaction stops
- CH3 + Cl = CH3Cl
22 of 22