Organic Chemistry Flashcards
What is structural isomerism
Compouds with the same molecular formula but different structural formula
What are the 3 types of structural isomer
Chain isomers
Positional isomers
Functional isomers
What is a chain isomer
Different length chain
The carbon skeleton can be arranged differently - e.g. Straight or branched chain
Similar chemical properties, but their physical properties e.g. Oiling point differ due to shape changes
Positional isomers?
Functional group in different position
Position of carbonate atom
Different chemical and physical properties
Functional isomers
The same atoms can be arranged into different unction all groups
VERY different chemical and physical properties
What is bond fission
When a reaction ( chemical) takes plac, bonds in the reactants break and the new bonds are formed in the products
COVALENT BOND BREAKS
What is homolyti fission
Each of the bonded atoms takes one of the shared pars of electrons from the bond
Each atom is called a radical and has 1 unpaired electron REACTIVE
Half headed curly arrow shows movement of single electrons
What is heteroLYTIC fission
ONe of the bonded atoms takes BOTH of the shared electrons
Atom takes both is called an anion and carries a lone pair
Double headed Curly arrow shows the movement of an electron pair
Types of reaction ?
Addition
Substitution
Elimination
Addition reactions
2 reactants join to form 1 product
Saturated molecule from an unsaturated one
Substitution reaction
An atom or group of atoms is replaced by a. Different atom or group of atoms
Elimination reaction
Removal of a small molecule from a larger one
One reactant = 2 products
What are alkanes
Saturated hydrocarbons
Only carbon and hydrogen, joined by covalent bonds
Cn H2n+2
Each carbon has 4 pairs of bonding electrons around it and they all repel one another equally = tetrahedral= 109.5
The bonding in alkanes
Sigma bond
2 orbitals overlapping
Each overlapping orbital contains 1 electron
One sp3 orbital
Boiling point of alkanes
Smaller alkanes have lower boiling points
Alkanes have COVALNET bonds inside the molecules - London forces hold the molecule together
The longer the carbon chain, the stronger the induced DD interaction- this is because there’s more surface area/ con at and more elecron pyrosis to interact
A branched chain has a LOWER boilin point than its straight chain isomer - can’t pack as closely tougher, have maker meocluelar surface areas
Reactivity of alkanes
Don’t react with most common reagents
C_C and C-H sigma bond is strong
C-C bond are NON polar
The electronegativity of C and h is so similar it can be considered non polar
Combustion - ALKANES
Alkanes react with a plentiful supply of o2 to form co2 and h2o
Gives out heat and alkanes are used as fuels
Compete combustion (alkanes)
Happens between gases - liquid alkanes are to be Vapourised first
Larger alkanes release more energy per mole because they have more atoms o react
Incomplete combustion of alkanes
If there is a limited supply of oxygen -Carbon monoxide produced and or C ( sooty flame
WHAT ARE THE requirements for a halogen + alkane reaction? And what is made
Halo alkane
- photochemical reaction
- UV required
- Hydrogen atom is replaced by chlorine and bromine= free radical substitution
Step 1 of free radical substitution
INTIITATION
- free radicals produced
- Sunlgiht provides enoug energy to break the halogen bond (photo dissociation)
- the bond splits equally ( HOMOLYTIC fission)
Step 2 of free radical substitution - making a halo alkane
Propagation
Free radicals used up and created in a chain reaction
- halogen ion attacks the alkane molecule
- New alkane (ion now) can attack other alkane molecules and so all the halogen or alkane molecules are used up
Step 3 of free radical substitution of halo alkane production
Termination
Free radicals mopped up
- if 2 free radicals join, they make a stable molecule
- Many possible termination reactions because there are lots of different radicals
Limitations of free radical substitution( halo alkane)
Lots of products can be formed( multiple substitution)
Free radical substitution can take place at any point along the carbon chain so a MIXTURE of isomers can be formed
Alkenes structure
UNSATURATED hydrocarbons
1 carbon to carbon double bond
Aliphatic Alkenes tat contain 1 double bond have the general forums Cn H 2n
Can be branched, contain more than 1 double bond or be cyclic
The double bond in an Alkene
Each carbon atom has 4 electrons in its outer shell and can use these electons to from bonds
For eac carbon atom of the double bond- 3 of 4 electons are used in 3 sigma bonds , one to the other arson atom of the double bond and the other 2 electrons to 2 other atoms( carbon or hydrogen)
Sigma bonds - alkanes
When 2 ‘s’ orbitals overlap in a straight line- this gives the HIGHEST POSSIBLE electron density between the 2 nuclei- this is a single COVALNET bond
The high electron density between the nuclei and the shared pair of electrons. This means that sigma bonds have a high bond enthalpy- strongest type of covalent bond
Pie bond
This leaves 1 electron on each carbon atom of the double bond not involved in sigma bond
This electron is in a P orbital
A pie bond is formed by the sideways overlap of 2 p orbitals, one from each carbon of the double bond
Each carbon atom contributes 1 electron to the electron pair in the pie bond and the pie electron density is concentrated above and below the line joining the nuclei of the bonding atom
Is rotation possible around every atom like in Alkenes, For alkanes ?
The pie bond locks the 2 carbon above in position and prevents them rotating around the double bond
This makes the GEOMETRY of Alkenes different from that of the alkanes where rotation is possible around every bond
Trigonal planar- Alkenes
There are 3 regions of electron density around each of the carbon atoms
The 3 regions repel each other as far apart as possible so the bond angle around each carbon atom is 120 degrees
All of the atoms are in the same place
What is the double double bond like in an alkene
- The C=C double bond is made of a sigma bond and a pie bond, the pie electron density is concentrated above and below the plane of the pie bond.
Why are alkanes unreactive
Contain C-C and C-H sigma bonds, which have a high bond enthalpy and so are difficult to break
The bonds are also NON POLAR so they don’t attract neucleophiles and electrophiles
why are alkanes less reactive than alkenes?
Alkanes only contain C-C and C-H which have a HIGH bond enthalpy and so are difficult to break
The bonds are also non polar so they don’t attract neucleophils and electrophils
Alkenes are more reactive than ALKANES because the C=C bond contains both a sigma and pi bond
why are alkenes more reactive than alkanes
the C=C double bond contains 4 electrons so it has a HIGH electron density and the pie bond also sticks out ABOVE and BELOW the rest of the molecule
this means pie bond is likely to be attacked by electrophiles - the low bond enthalpy of the pie bond also contributes to alkene reactivity
what addition reactions do alkenes undergo with ?
Hydrogen
Halogens
Halogen Halides
Steam in the presxense of an acid catalyst
What is an electrophile
A reactant that attacks an area of HIGH electron density where it accepts a pair of electrons to form a new covalent bond
electrophiles are often ?
Positive ions
A molecule containing an atom with a delta + charge
CAN be non polar too
step 1 of electrophilic addition
- The positive charge on the electrophile is attracted to the electron density in the double bond
- As the electrophile approaches the double bond, electrons in the A-B bond are repelled towards B - INDUCING A DIPOLE
- The pi bond breaks and A bonds to the carbon, forming a carbocation - an ion with a positively charged carbon atom
- The 2 electrons in the AB bond move to B forming a B- ion
step 2 of electrophilic addition
B - ion acts as a nucleophile ( nuc) attack’s the carbonation - the lone pair in the B- ion are attracted towards the positive charged carbon in the carbonation , causing B to bond to it
neuclophile
attack carbon ( delta positive)
usually with a lone pair
HYDROGENATION reaction
alkene - alkane
what happens in a hydrogenation reaction ( alkene - alkane)
REACTANT- Hydrogen
CONDITIONS- nickel catalyst and high temps
Type of reaction - addition / reduction
Halogenation
Alkene - dihaloalkane
What is a halogenation reaction ?
Reagent - bromine
Conditions - doom
Temp
Mechanism - electrophilic reaction
Bond fission - heterolytic
Example of halogenation with ethene and br 2?
- Double bond repels the electrons in Br2, polarising BR-BR induced dipole
- Heterolytic( unequal) fission of Br2. The closer Br gives up the bonding electrons to the other Br + bonds to the carbon atoms
- You get a positively charged carbocation immediate Br- now zooms over
- Bonds to other C atom, forming 1,2 dibromoethane
How to use bromine water to test for carbon double bonds
Shake an alkene with orange bromine water, the solution quickly decolourises
this is because bromine is added across the double bond to form a colourless dibromoalkane
Alkene – halo alkane
Reagant- hydrogen bromide or hydrogen chloride
Room temperature
ELECTROPHILIC ADDITION
Explain what happens to form a halo alkane from an Alkene
Hydrogen bromide and Alkene
- Bromine is more electronegative than huge on, so hydrogen bromide is polar
- The electron pair in the pie bond is attracted to the partially positive hydrogen atoms, causing the double bond to break
- The bond rooms between the huge on atom of the H-Br molecule and a carbon atom that was part of the double bond
- The H-Br bond breaks by HETEROLYTIC fission
- Br- ion and carbocation for med
- BR- ion reacts with carbocation to form addition product
What happens when you combine an e.g. Hydrogen halide) is added to an unsymmetrical Alkene
2 possible products can be formed
The amount of each product depends on how stable the carbocation formed in the middle of the reaction is
Carbocations with more ALKYL groups are more stable because the alkyl groups feed electrons towards the positive charge
The more stable a carbocation the more libel it is to form
What is a primary carbocation
1 alkyl group attached to positive charged carbon
Secondary carbocation
2 alkyl groups attatche to positively charged carbon
Tertiary carbocation
3 alkyl groups attatched to positively charged carbon
What’s more stable- a primary or tertiary carbocation
TERTIARY
What does major and minor mean ( unstable Alkenes–alkanes)
Major = more stable
Doesn’t go back to double bonds
What is markowinioffs rule
The major product from addition of a halogen halide to an unsymmetrical Alkene is one where hydrogen affairs to the carbon with the most hydrogens already attached
Reactions with Alkenes + steam
= ALCOHOL
Steam( h20)
Steam is adde across the double bond
This affliction reaction is used in industry to produce ethanol from there
What is addition polymerisation
Something unsaturated Alkene molecules undergo to produce long, saturated chains ( no double bonds )
Each have specific property depending on monomer used
What is a repeat unit
Specific arrangement of atoms - repeated over and over
Why aren’t polymers biodegradable
Lack of reactivity
LANDFILL
- Way to deal with waste plastics
- Used when the plastic is…
= difficult to separate from other waste
= not in sufficient quantities to make separation financially worthwhile
= too difficult technically to recycle - After rubbish is buried in lined holes - so contamination of water table doesn’t occur- DOESNT DECOMPOSE due to anerobic conditions
COMBUSTION
Organic compounds in polymers and other waste can be burnt to product energy
Large quantities of co2 produced and toxic gases such as HCl( if polymer is chlorinated)
Some companies use bases( BAWS) e.g. Ca0 to neutralise
RECYCLING
Reduces their environmental impact by conserving finite fossil fuels and decreasing amounts going to landfill)
SORTED, chopped, washed and melted- cut into pellets and reused
PVC recycling
HAZARDOUS disposal and recycling
Dumping PVC In landfill - not sustainable
It is buried however it releases HCL and other pollutants
New technology- solvents dissolve PVC, it’s then recorded by precipitation form solvent and solvents reused
FEEDSTOCK
CHEMICAL and thermal processes that cna reclaim monomers, gases, or oil from waste polymers
The pod cut form feedstock recycling resemble these produced from crude oil in refineries
These materials can be used as RAW materials for production of new polymer
Biodegradable polymers
Broken down by microorganisms into water, co2, or biological compounds
Made from starch, cellulose , oil factors or contain additives that alter the structure of traditional polymers - so they can be broken down
Need the right conditions to decompose- compost
Compost able polymers degrade and leave no toxic residue( polylatic acid)
Supermarket bays made from plant starch -used as bin liners for food waste( water and bag can oth be composed)
Compostable plates and cups from sugar cane fibres
PHOTODEGRADABLE polymers
Contain bonds that are weakened by absorbing light
Oil based
Or - add light - absorbing additives
