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Alevel CHEM > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

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1
Q

What is structural isomerism

A

Compouds with the same molecular formula but different structural formula

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2
Q

What are the 3 types of structural isomer

A

Chain isomers
Positional isomers
Functional isomers

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3
Q

What is a chain isomer

A

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

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4
Q

Positional isomers?

A

Functional group in different position
Position of carbonate atom
Different chemical and physical properties

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5
Q

Functional isomers

A

The same atoms can be arranged into different unction all groups
VERY different chemical and physical properties

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6
Q

What is bond fission

A

When a reaction ( chemical) takes plac, bonds in the reactants break and the new bonds are formed in the products
COVALENT BOND BREAKS

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7
Q

What is homolyti fission

A

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

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8
Q

What is heteroLYTIC fission

A

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

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9
Q

Types of reaction ?

A

Addition
Substitution
Elimination

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10
Q

Addition reactions

A

2 reactants join to form 1 product

Saturated molecule from an unsaturated one

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11
Q

Substitution reaction

A

An atom or group of atoms is replaced by a. Different atom or group of atoms

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12
Q

Elimination reaction

A

Removal of a small molecule from a larger one

One reactant = 2 products

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13
Q

What are alkanes

A

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

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14
Q

The bonding in alkanes

A

Sigma bond
2 orbitals overlapping
Each overlapping orbital contains 1 electron
One sp3 orbital

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15
Q

Boiling point of alkanes

A

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

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16
Q

Reactivity of alkanes

A

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

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17
Q

Combustion - ALKANES

A

Alkanes react with a plentiful supply of o2 to form co2 and h2o
Gives out heat and alkanes are used as fuels

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18
Q

Compete combustion (alkanes)

A

Happens between gases - liquid alkanes are to be Vapourised first
Larger alkanes release more energy per mole because they have more atoms o react

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19
Q

Incomplete combustion of alkanes

A

If there is a limited supply of oxygen -Carbon monoxide produced and or C ( sooty flame

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20
Q

WHAT ARE THE requirements for a halogen + alkane reaction? And what is made

A

Halo alkane

  • photochemical reaction
  • UV required
  • Hydrogen atom is replaced by chlorine and bromine= free radical substitution
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21
Q

Step 1 of free radical substitution

A

INTIITATION

  • free radicals produced
  • Sunlgiht provides enoug energy to break the halogen bond (photo dissociation)
  • the bond splits equally ( HOMOLYTIC fission)
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22
Q

Step 2 of free radical substitution - making a halo alkane

A

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
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23
Q

Step 3 of free radical substitution of halo alkane production

A

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

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24
Q

Limitations of free radical substitution( halo alkane)

A

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

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25
Q

Alkenes structure

A

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

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26
Q

The double bond in an Alkene

A

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)

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27
Q

Sigma bonds - alkanes

A

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

28
Q

Pie bond

A

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

29
Q

Is rotation possible around every atom like in Alkenes, For alkanes ?

A

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

30
Q

Trigonal planar- Alkenes

A

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

31
Q

What is the double double bond like in an alkene

A
  • 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.
32
Q

Why are alkanes unreactive

A

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

33
Q

why are alkanes less reactive than alkenes?

A

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

34
Q

why are alkenes more reactive than alkanes

A

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

35
Q

what addition reactions do alkenes undergo with ?

A

Hydrogen
Halogens
Halogen Halides
Steam in the presxense of an acid catalyst

36
Q

What is an electrophile

A

A reactant that attacks an area of HIGH electron density where it accepts a pair of electrons to form a new covalent bond

37
Q

electrophiles are often ?

A

Positive ions
A molecule containing an atom with a delta + charge
CAN be non polar too

38
Q

step 1 of electrophilic addition

A
  • 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
39
Q

step 2 of electrophilic addition

A

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

40
Q

neuclophile

A

attack carbon ( delta positive)

usually with a lone pair

41
Q

HYDROGENATION reaction

A

alkene - alkane

42
Q

what happens in a hydrogenation reaction ( alkene - alkane)

A

REACTANT- Hydrogen
CONDITIONS- nickel catalyst and high temps

Type of reaction - addition / reduction

43
Q

Halogenation

A

Alkene - dihaloalkane

44
Q

What is a halogenation reaction ?

A

Reagent - bromine

Conditions - doom
Temp

Mechanism - electrophilic reaction

Bond fission - heterolytic

45
Q

Example of halogenation with ethene and br 2?

A
  • 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
46
Q

How to use bromine water to test for carbon double bonds

A

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

47
Q

Alkene – halo alkane

A

Reagant- hydrogen bromide or hydrogen chloride
Room temperature
ELECTROPHILIC ADDITION

48
Q

Explain what happens to form a halo alkane from an Alkene

Hydrogen bromide and Alkene

A
  1. Bromine is more electronegative than huge on, so hydrogen bromide is polar
  2. The electron pair in the pie bond is attracted to the partially positive hydrogen atoms, causing the double bond to break
  3. The bond rooms between the huge on atom of the H-Br molecule and a carbon atom that was part of the double bond
  4. The H-Br bond breaks by HETEROLYTIC fission
  5. Br- ion and carbocation for med
  6. BR- ion reacts with carbocation to form addition product
49
Q

What happens when you combine an e.g. Hydrogen halide) is added to an unsymmetrical Alkene

A

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

50
Q

What is a primary carbocation

A

1 alkyl group attached to positive charged carbon

51
Q

Secondary carbocation

A

2 alkyl groups attatche to positively charged carbon

52
Q

Tertiary carbocation

A

3 alkyl groups attatched to positively charged carbon

53
Q

What’s more stable- a primary or tertiary carbocation

A

TERTIARY

54
Q

What does major and minor mean ( unstable Alkenes–alkanes)

A

Major = more stable

Doesn’t go back to double bonds

55
Q

What is markowinioffs rule

A

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

56
Q

Reactions with Alkenes + steam

A

= ALCOHOL
Steam( h20)
Steam is adde across the double bond
This affliction reaction is used in industry to produce ethanol from there

57
Q

What is addition polymerisation

A

Something unsaturated Alkene molecules undergo to produce long, saturated chains ( no double bonds )
Each have specific property depending on monomer used

58
Q

What is a repeat unit

A

Specific arrangement of atoms - repeated over and over

59
Q

Why aren’t polymers biodegradable

A

Lack of reactivity

60
Q

LANDFILL

A
  • 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
61
Q

COMBUSTION

A

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

62
Q

RECYCLING

A

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

63
Q

PVC recycling

A

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

64
Q

FEEDSTOCK

A

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

65
Q

Biodegradable polymers

A

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

66
Q

PHOTODEGRADABLE polymers

A

Contain bonds that are weakened by absorbing light
Oil based
Or - add light - absorbing additives

Alevel CHEM (13 decks)

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