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IB Chemistry HL > 10/20 organic chemistry > Flashcards

10/20 organic chemistry Flashcards

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1
Q

empirical formula

A

the formula that gives the simplest whole number ratio of the different types of atom within the compound

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2
Q

molecular formula

A

shows the number of each type of atom present. nothing about bonding

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3
Q

structural formula

A

shows how the surrounding atoms and groups are arranged around successive carbon atoms in the backbone chain of the molecule. other than for cyclic structures, no bonding is shown.

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4
Q

displayed formula

A

shows all of the atoms and the bonds (represented as lines)

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5
Q

skeletal formula

A

most hydrogen atoms are omitted and the line ends or vertices represent carbons. functional groups and atoms other than carbon or hydrogen are still shown. easiest to draw and commonly used.

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6
Q

alkane suffix

A

-ane

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7
Q

alkene suffix

A

-ene

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8
Q

alkene suffix

A

-yne

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9
Q

alcohol suffix

A

-ol

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10
Q

aldehyde suffix

A

-al

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11
Q

ketone suffix

A

-one

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12
Q

carboxylic acid suffix

A

-oic acid

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13
Q

ester suffix

A

-yl -oate

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14
Q

1 prefix

A

meth

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15
Q

2 prefix

A

eth

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16
Q

3 prefix

A

prop

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17
Q

4 prefix

A

but

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18
Q

5 prefix

A

pent

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19
Q

6 prefix

A

hex

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20
Q

7 prefix

A

hept

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21
Q

8 prefix

A

oct

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22
Q

what is the functional group for an alkene

A

a double bond between carbons

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23
Q

what is the functional group of halogenoalkane

A

a single bond to a halogen

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24
Q

alcohol functional group

A

a single bond to an oxygen and then a single bond to a hydrogen

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25
Q

aldehyde functional group

A

a double bond to a oxygen and a single bond to a hydrogen

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26
Q

ketone functional group

A

a double bond to an oxygen from a carbon

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27
Q

carboxylic acid functional group

A

a double bond from a carbon to an oxygen, and also a single bond to an oxygen with another single bond to a hydrogen. it is a ketone and an alcohol

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28
Q

nitrile functional group

A

a triple bond to a nitrogen from a carbon

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29
Q

amine functional group

A

2 single bonds to hydrogens from a nitrogen

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30
Q

acyl chloride functional group

A

a double bond to a oxygen and a single bond to a chlorine all from a carbon. like a ketone and a halogenoalkane

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31
Q

acid anhydride functional group

A

an oxygen is inbetween two carbons. on each of the carbons there is a double bond to an oxygen.

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32
Q

ester functional group

A

a double bond to an oxygen from a carbon which also has a single bond to an oxygen which has a single bond to something else

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33
Q

amide functional group

A

the carbon has a double bond to an oxygen. the nitrogen connected to the carbon by a single bond has 2 hydrogens of single bonds. like a ketone and an amine.

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34
Q

what is organic chemistry

A

the study of carbon compounds

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35
Q

what was vitalism

A

the idea that organic molecules had distincitve chemical properties, making them unique to living organisms.

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36
Q

how was vitalism rebuked

A

german chemist friedrich wohler synthesised urea from inorganic materials, in the absence of any biological tissue. he found that ammonium cynate is urea. he showed organic molecules were not unique to living organisms.

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37
Q

why do alkanes make good fuels

A

they react with oxygen in exothermic reactions to produce carbon dioxide and water.

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38
Q

as molar mass increases, and the strength of the intermolecular forces between the molecules increase, what happens

A

melting and boiling points rise. this explains why the first four members of the alkanes, methane to butane, are gases but pentane and hexane are liquids. from C17H36 onwards, the alkanes are waxy solids

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39
Q

what is a homologous series

A

a homologous series is a group of organic compounds that:

contain the same functional group,

have the same general formula,

differ by a CH2 group,

have similar chemical properties,

show a gradation in physical properties such as boiling point.

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40
Q

how many covalent bonds does carbon form

A

4

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41
Q

why is carbon so special as opposed to silicon

A

although both are in group 14, and so have 4 covalent bonds to make, carbon-hydrogen bonds are stronger than silicon-hydrogen bons

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42
Q

addition reaction

A

reaction where a molecule joins to an unsaturated molecule to produce a saturated molecule

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43
Q

aliphatic

A

organic compounds containing C chains and branches

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44
Q

aromatic

A

organic compounds containing one or more benzene rings

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45
Q

carbocation

A

a positive ion containing one or more benzene rings

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46
Q

cyclic

A

organic compounds containing c rings (not aromatic rings) also called alicyclic

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47
Q

dehydrogenation

A

elimination of hydrogen

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48
Q

electrophile

A

long pair acceptor

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49
Q

elimination reaction

A

reaction where a molecule is lost from a saturated molecule to form an unsaturated molecule

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50
Q

free radical

A

species with an unpaired electron

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51
Q

functional group

A

the atom or group of atoms that is responsible for most of the chemical reactions of a molecule

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52
Q

homologous series

A

a family of compounds with the same general formula and similar chemical properties. in a series, each member differs by the addition of a CH2 group and there is a gradual change in physical properties

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53
Q

hydrogenation

A

addition of hydrogen (over heat and a nickel catalyst)?

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54
Q

hydroloysis

A

a reaction involving the breaking of bonds due to reaction with water

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55
Q

nucleophile

A

lone pair doner

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56
Q

organic chemistry

A

study of compounds containing carbon

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57
Q

saturated

A

molecule containing no double bonds

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58
Q

sterioisomers

A

molecules with the same molecular and structural formulae but with different spatial arrangement of atoms

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59
Q

geometric isomers

A

type of stereoisomerism. molecule which have different arrangements of groups around C=C

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60
Q

optical isomers

A

type of stereoisomerism. molecules which are non-superimposable mirror images.

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61
Q

structural isomers

A

molecules with the same molecular formula but different structures

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62
Q

chain isomers

A

type of stereoisomerism. structural isomers that differ by having a different carbon chain

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63
Q

position isomers

A

type of stereoisomerism. structural isomers that differ by having the functional group in a different position

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64
Q

functional group isomers

A

type of stereoisomerism. structural isomers that differ by having a different functional group.

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65
Q

substitution reaction

A

reaction where an atom/group replaces another atom/group

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66
Q

unsaturataed

A

molecule containing double bonds

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67
Q

isomers have

A

the same molecular formula but different displayed formulas

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68
Q

types of structural isomerism

A

chain isomerism

position isomerism

functional group isomerism

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69
Q

example of a chain isomer

A

pentane and 2-methylbutane

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70
Q

the greater the number of carbon atoms in the molecular formula

A

the greater the number of possible isomers

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71
Q

examples of positional isomers in C4H8

A

but-1-ene

but-2-ene

2-methylpropene

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72
Q

examples of functional group isomerism

A

propanal and propanone

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73
Q

alkyne suffix

A

-yne

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74
Q

alkyne fucntional group

A
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75
Q

ether prefix

A

prefix: alkoxy
e. g. methoxy

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76
Q

ether functional group

A
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77
Q

arene suffix

A

benzene

or prefix: phenyl

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78
Q

arene functional group

A
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79
Q

what can functional groups be classified as

A

acidic or basic

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80
Q

what do compounds containing a carboxyl functional group do to form the carboxylate ion (R-COO(-))

A

donate a proton

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81
Q

how do amines become a base

A

using a lone pair of electrons on the nitrogen atom to accept a proton

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82
Q

chain isomersim is effectively

A

changing the carbon skeletons

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83
Q

posisitional isomerism is effectively

A

the position of the functional group moves but NOT the carbon skeleton

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84
Q

functional group isomerism

A

same carbon skeleton but with completely different functional groups or homogolous series

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85
Q

types of steroisomers

A

geometric

optical

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86
Q

stereoisomers defintion

A

molecules with the same structural formula but a different spatial arrangement of atoms

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87
Q

structural isomes definition

A

molecules with the same molecular formula but a different structure

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88
Q

volatility is

A

The measure of how easily a substance evaporates

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89
Q

Substances that have stronger intermolecular forces are

A

less volatile and consequently have higher boiling points.

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90
Q

how does increasing molar mass increase boiling point

A

As a consequence of the increasing molar mass, there are stronger London dispersion forces between the molecules, which result in an increase in the boiling point. Therefore, the early members of a homologous series such as the alkanes are usually gases or liquids at room temperature, while the later members are usually solids.

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91
Q

how do branched and chain isomers usually have different boiling points

A

The branching of a chain produces a more spherical shape to the molecule. This results in less surface contact between the molecules than with straight-chain isomers. Therefore, branched-chain isomers have weaker intermolecular forces and, consequently, lower boiling points

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92
Q

how does the functional group change the boiling point

A

Polar functional groups result in stronger dipole–dipole interactions between the molecules, and therefore higher boiling points. Compounds with functional groups that contain O-H or N-H bonds are capable of forming hydrogen bonds between their molecules. This is the reason for the difference in volatility between ethers and their isomeric alcohols. The lack of hydrogen bonding between their molecules means that ethers evaporate at lower temperatures than alcohols with similar molar masses.

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93
Q

what should you do when comparing boiling points of various molecules

A

try to keep the molar mass the same

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94
Q

what does solubuility of molecules depend on

A

their ability to form hydrogen bonds with water molecules

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95
Q

increasing size of the carbon chain, increases the hydrophobic character of the molecule,

A

decreasing its solubility in polar solvents like water

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96
Q

hydrophobic

A

the non-polar hydrocarbon chain of a molecule which is insoluble in polar solvents such as water.

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97
Q

increasing strength of intermolecular force

A
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98
Q

carboxylic acids can form what through hydrogen bonds

A

dimers, between the two carboxyl groups

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99
Q

key organic functional groups

A

alkanes

alkenes

alcohols

halogenoalkanes

aromatic compounds like benzene

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100
Q

what happens due to alkanes having low reactivity

A

they undergo free radical substitution reactions

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101
Q

a small proportion of nations have control over the worlds oil resouces. the interdependence of the countries that are net importers and those that are net exporters…

A

is an important factor in shaping global policies and economic developments

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102
Q

how does methane contribute to greenhouse gas emissions

A

through agriculture and landfills

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103
Q

temperature of thermal cracking

A

900 celsius

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104
Q

temperature of catalytic cracking

A

450 celsuius

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105
Q

atm of thermal cracking

A

70

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106
Q

atm of catalytic cracking

A

1-2 atm

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107
Q

what catalysts are used in thermal cracking

A

none

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108
Q

what catalysts are used in catalytic cracking

A

zeolites

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109
Q

what products are made from thermal cracking

A

alkenes

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110
Q

what products are made from catalytic cracking

A

motor fuels

aromatic hydrocarbons

cyclic alkanes

branched alkanes

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111
Q

where are zeolites found

A

they are natural occuring and can be manufactured

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112
Q

what is an octane ratign

A

a standard measure of the fuel used in cars and aircraft

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113
Q

how is carbon dioxide formed

A

complete combustion

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114
Q

potential problems of carbon dioxide

A

greenhouse gas causing global warming

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115
Q

solutions to reduce carbon dioxide

A

burn less fossil fuels

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116
Q

how is carbon monixde formed

A

incomplete combustion

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117
Q

potential problems of carbon monoxide

A

toxix

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118
Q

ways to reduce carbon monoxide

A

ensure a good supply of air and oxygen when burning fuel

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119
Q

how is carbon fomed

A

incomplete combustion

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120
Q

potential problems with carbon

A

blackens buildings

global dimming

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121
Q

ways to reduce carbon

A

ensure good supply of air and oxygen when burning fuels

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122
Q

how is sulfur dioxide formed

A

combustion of sulphur in fuel

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123
Q

potential problems with sulfur dioxide

A

acid rain

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124
Q

how to reduce sulfur dioxide

A

remove sulphur before buring or remove so2 after burning (flue gas desulferization)

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125
Q

how are nitrogen oxides formed

A

reaction of N2 in air with O2 at very high temperatures (often in engines or furnaces)

126
Q

problems of nitrogen oxides

A

acid rain

127
Q

how to reduce nitrogen oxides

A

for engines, use a catalytic converter

128
Q

how are unburned fuels formed

A

not all fuel burns

129
Q

potential problems with unburned fuels

A

wastes fuel, harmful and a greenhouse gas

130
Q

ways to reduce unburned fuel

A

ensure correct fuel:air mixture when fuel is burned

131
Q

what does acid rain do

A

damage vegetation

kill fish

damage e.g. limestone

132
Q

flue gas desulphurisation system

A
133
Q

describe how sun enters and exits the earths atmosphere

A

enters as incoming short wave raditaion

long wave radiation, most escapes to outer space, cooling the earth.

but some is trapped by greenhouse gases, which warms the planet.

134
Q

longer chain lengths…

A

increase boiling point

135
Q

branched isomers…

A

have lower boiling points

136
Q

boiling points of the alkanes

A

-162 (methane) to 36 (pentane)

137
Q

boiling points of methylalkanes

A

-12 (methylpropane) and 28 (methylbutane)

138
Q

why do longer carbon chains have higher boiling points

A

stronger van der Waal’s forces between molecuels (more electrons in the molecules)

139
Q

why do branched isomers have lower boiling points

A

weaker van der Waals forces between molecules (due to moelcules not being able to pack as close together)

140
Q

basic idea of fractional distillation

A

crude oil is vapourized

the vapour is passed into a tower which is hot at the bottom

as the vapour rises it cools

molecules will condense at different heights as they have differetn boiling points

the larger the molecules, the lower down the column it condenses

141
Q

fraction definition

A

a mixture of hydrocarbosn with similar boiling points

142
Q

as carbon chain gets longer, the hydrocarbons:

A

become more viscous

harder to ignite

less volatile

have higher boiling points

143
Q

what is cracking

A

thermal decomposition of alkanes

144
Q

complete combustion equation

A

alkane + oxygen –> carbon dioxide + water

145
Q

incomplete combustion equation

A

alkane + oxygen –> carbon + water

146
Q

how can impurities containing sulfur be removed

A

using afurnace by flue gas desulferisation

147
Q

give the equation for how gases pass through a scrubber containing calcium oxide or calcium carbonate which reacts with the sulfur dioxide

A

CaO + SO2 –> CaSO3
or
CaCO3 + SO2 –> CaSO3 + SO2

148
Q

what is the type of reaction for when gases pass through a scrubber containing calcium oxide or calcium carbonate which reacts with the sulfur dioxide

A

acid base as CaCO3 and CaO are bases and SO2 is an acidic oxide. (non-metal oxide)

CaO + SO2 –> CaSO3
or
CaCO3 + SO2 –> CaSO3 + SO2

149
Q

what do catalytic converters do

A

remove CO, NOx, and unburned hydrocarbons from exhaust gases, making them CO2, N2 and H2O

150
Q

what do catalytic convertes have to make them have a large surface area

A

a ceramic honeycomb coated with a thin layer of catalyst metals (Pt, Pd, Rh)

151
Q

briefly explain global warming

A

the burning of fossil fuels including alkanes releases carbon dioxide into the atmosphere.

carbon dioxide, methane and water vapour are all greenhouse gases. they trap heat in the earths atmosphere.

they absorb IR emitted by the earth due to bond vibrations.

water is the main greenhouse gas, but is natural, followed by carbon dioxide and methane.

152
Q

what are haloalkanes

A

saturated molecueles made of carbon and hydrogen and halogens

153
Q

alkane + hydrogen –>

A

haloalkane + hydrogen halide

154
Q

traces of products from further subsititution in the methane + chlorine –> chloromethane + hydrogen chloride reaction

A

CH2Cl2

CHCl3

CCl4

C2H6

155
Q

stages of free radical substitution

A

inititation

propogation

termination

156
Q

what do arrows show in org chem

A

electrons movement

157
Q

initiation

A
158
Q

propogation

A
159
Q

termination

A
160
Q

what is the first step for propogation

A

beginning reactant + free radical halogen –> halogen halide + beginning reactant free radical (one less hydrogen)

161
Q

what is the second step for propogation

A

the beginning reactant free radical + halogen molecule –> ending product + halogen free radical

162
Q

what is the UV light for

A

to break the single covalent bond of the halogen

163
Q

properties of small alkanes

A

low boiling points

runny

easy to ignite

burns with clean flame

164
Q

properties of big alkanes

A

high boiling points

viscous

hard to ignite

burns with smoky flame

165
Q

what increases from small to big alkanes

A

boiling points

viscosity

flammability

flame gets dirtiers

166
Q

for what fractions is demand higher than supply

A

petrol and disel

NOT kerosene or fuel oil

167
Q

cracking image

A
168
Q

conditions required for crackung

A

aluminium oxide catalyst AND high temperatures of 600-700 celsius

169
Q

test for alkanes/akenes

A

add bromine water.

in cyclohexane it forms an orange layer on top of a slightly yellow layer and does not mix

in cyclohexene it declourises and does not mix.

170
Q

vegetable oils + ??? —> shortening/margarine

A

H2 over heat, nickel catalyst

171
Q

saturated fatty acids have

A

carbon carbons single bonds

172
Q

unsaturated fatty acids have

A

carbon carbond double bond

173
Q

trans fatty acids have

A

hydrogen bonds on opposite sides of the chain of carbon-carbon single bonds

174
Q

what reaction do alkenes undergo

A

addition reactions, small molecules add across the C=C

175
Q

what type of double bond do alkenes contain

A

an electron rich double bond which attracts species (molecules/ions) which are electron poor and seeking a lone pair called electrophiles. also described as lewis acids.

176
Q

what do electrophiles do

A

add across the double bond to form new, saturated products with the pi-bond of the alkene being broken in the process.

177
Q

stages of alkene addition reaction (electrophilic addition)

A

the halogen/interhalogen/hydrogen halides (e.g. Br-Br or or H-Br) is either polar already or experiences an induced dipole due to the four electrons in the C=C.

the pi-bond breaks (first arrow bringing the pair of electrons from the C=C to the top atom of the hal.etc.

the hal.etc. bond breaks

the top atom of the hal.etc. is attracted and the alkene double bond folds out.

the remaining carbon atom has a positive charge as it still requires one more covalent bond.

the remaining hal.etc. is negative. it is attracted to the remaining carbon atom.

178
Q

priamry, secondary, tertiary carbocation

A
179
Q

what is markonikov’s rule

A

in the addition of a compound HX to an unsaturated compound, hydrogen becomes attatched to the unsaturated carbon with the larger number of hydrogen atoms already attatched.

180
Q

what is the least stable carbocation

A

primary carbocation. secondary and tertairy increase alongside stability.

181
Q

carbocation stability increases with the number of attatched…

A

alkyl groups

182
Q

When hydrogen halides undergo reactions with an asymmetric alkene, there are

A

two possible products, depending on which carbon atom in the double bond the hydrogen atom bonds with.

183
Q

polymer def

A

long chain molecule made from lots of small molecules joined together

184
Q

monomer def

A

small molecules that join together to make polymers

185
Q

addition polymerisation def

A

formation of long chain molecules from lots of small molecules joining together with no other products

186
Q

which structure has brackets and an n

A

the polymer structure

NOT the repeating unit

187
Q

low density poly(ethene)

A

molecules loosely packed due to branching

flexible and soft

bags, cling film

188
Q

high density poly(ethene)

A

molecules tightly packed

stiffer and harder

buckets, bottles

189
Q

uses of ethene

A

LPDE
HPDE

190
Q

uses of methylethene

A

plastic bottles

191
Q

uses of phenylethene

A

packaging

crates/ropes

192
Q

uses of chloroethene

A

pipes

window frames

193
Q

uses of tetrafluroethene

A

non stick pans

194
Q

uses of methyl 2-cyanopropenoate

A

adhesives/super glue

195
Q

uses of methyl 2-methyl propenaoate

A

glass substitute windows/rulers

196
Q

common everyday name for methylethene

A

polypropylene

197
Q

common everyday name for phenylethene

A

polystyrene

198
Q

common everyday name for chloroethene

A

PVC

199
Q

common everyday name for tetrafluroethene

A

PTFE/teflon

200
Q

common everyday name for methyl-2-cyanopropenoate

A

super glue

201
Q

common everyday name for methyl-2-methylpropenoate

A

PMMA/perspex

202
Q

what happens when you mix water and ethanol

A

initally, a cloudy mixture is formed. then it becomes clearless because they are miscible liquids

203
Q

what happens when you mix ethanol and a rice grain sized of sodium

A

small bubbles of hydrogen gas

204
Q

what happens when you mix dilute sulphuric acid and potassium dichromate in a test tube, then add some ethanol and warm in a water bath

A

green –> grey. shows oxidation has occured.

205
Q

what happens when you mix dilute sulphuric acid and potassium dichromate in a test tube, then add some propan-2-ol and warm in a water bath

A

green–> grey. this shows oxidation has occured.

206
Q

what happens when you mix dilute sulphuric acid and potassium dichromate in a test tube, then add some methylpropan-2-ol and warm in a water bath

A

nothing. methylpropan-2-ol and other tertiary carbocations cannot oxidise alcohols.

207
Q

what happens in tollens reagent

when silver nitrate and ammonium hydroxide are mixed until silver oxide precipitate just dissolves, and an aldehyde is added.

A

greyish precipitate

208
Q

what happens in tollens reagent

when silver nitrate and ammonium hydroxide are mixed until silver oxide precipitate just dissolves, and a ketone is added.

A

no reaction

209
Q

what happens in fehling’s solution

Fehling’s A and Fehling’s B are mixed with a few drops of aldehyde

A

a deep blue colour with a precipitate ont op

210
Q

what happens in fehling’s solution

Fehling’s A and Fehling’s B are mixed with a few drops of ketone

A

no reaction

211
Q

primary alchols have

A

one R group on the carbon attatched to the OH group

212
Q

secondary alcohols have

A

two R groups on the carbon attatched to the OH group

213
Q

tertiary alcohols have

A

three R group on the carbon attatched to the OH group

214
Q

solubility in water ________ decreases with increasing size of hydrocarbon chain e.g. pentanol and hexanol are not particularly soluble in water.

A

decreases

215
Q

oxidation of alcohols

A

where the alcohol gains oxygen atoms and loses hydrogen atoms. in organic chemistry, an oxidation reaction is usually represented by using the symbol (O) for the oxidising agent.

216
Q

what is the oxidising agent for alcohols

A

heated acidified potassium dichromate

217
Q

what is the colour change of dichromate when heated and acidified

A

orange to green

218
Q

what is the equation for when chromate is heated and acidified

A

Cr2O7^2- –> Cr^3+

219
Q

stages of primary alchols when oxidised

A

alcohol

aldehyde

carboxylic acid

220
Q

stages of secondary alchols when oxidised

A

alcohol

ketone

no reacton

221
Q

stages of tertiary alcohols when oxidised

A
222
Q

what is the colour change for potassium manganate when heated

A

from purple to a very pale pink

223
Q

what do you do if you want to collect the intermediary product (aldehyde) when oxidising a primary alcohol and you dont want the carboxylic acid.

A

use distillation. you can take advantage of different boiling points as the aldehyde is bonded through dipole dipole intermolecular forces, meaning it has a lower boiling point than for the the alcohol or carboxylic acid which both use hydrogen bonding. so you can take it out of the column first.

224
Q

what are esters derived from

A

carboxylic acids

225
Q

applications of esters

A

flavouring agents and medications and solvents and explosives

226
Q

what is esterification

A

a reversible reaction where a carboxylic acid and an alcohol are heated in the presence of a catalyst, normally concentrated sulfuric acid.

227
Q

what are the wavelengths of visible light range

A

400-700 nm

228
Q

carboxylic acids + alcohols (with concentrated H2SO4 catalyst) makes…

A

esters

229
Q

are esterification reacations reversible

A

most are

230
Q

because H2O is formed, what else can esterification reactions be described as

A

condensation

231
Q

what is the reverse reaction of an esterfication called

A

hydrolysis

232
Q

what is the role of suphuric acid in esterifications

A

catalyses the reaction

233
Q

why is the sodium carbonate used to pour the esters into in esterifcations

A

neutralises the sulphuric acid and stops the reaction

234
Q

what pieces of evidence shows the Keuk;e structure was wrong

A

the carbon to carbon bond lengths were all identical (if they are double/single alternating, the bonds should have alternating lengths)

only one isomer exists (there should be two if alternating double/single bonds

enthalpy change of hydrogenation of benzene is too low

235
Q

what reactions does benzene readily undergo

A

combustion
substitution

236
Q

why does benzene undergo electrophilic substitution reactions

A

because electrophiles are attracted to regions of negative charge such as the electron-rich benzene ring.

237
Q

what is an electrophilic reaction

A

replacement of a hydrogen atom with an electrophile.

238
Q

what is the backside attack realted to

A

sn2

239
Q

what is the backside attack

A

a term used to refer to the approach of the nucleophile to the electron-deficient carbon from the opposite side of the leaving group.

240
Q

what occurs at the same time as the attack of the nucelophile

A

the departure of the halide

241
Q

stages of an sn2 reaction

A
242
Q

difference in sn2 and sn1

A

in sn1 the loss of the halide occurs ebfore the addtion fo the nculeophile.

in sn2 they cocur at the same time

243
Q

what does the rate of reaction of the sn2 reaction depend on

A

concentration of both the alkyl halide and the nuclophile

244
Q

stages of the sn1 reaction

A

carbon-halogen bond breaks heterolytically (halogen atom takes both electrons) resulting in a carbocation intermediate. this has the highest activation energy because of the attraction between the positively charged ions. then the nuclophile joins

245
Q

what is steric hindrance

A

the three bulky methyl groups on a sn1 reaction following the loss of the halogen. making it difficult for the incoming nucleophile to attack from the abckside.

246
Q

how is the carbocation stablised in sn1 reactions

A

by each of the buljky methyl froups having an electron donating effect (or psotiive inductive effect)

247
Q

incresing carbocation stability

A

primary

secondary

tertiary

248
Q

protic polar solvents (ethanol, ammonia, water) faavour which type of reaction

A

sn1

249
Q

why do protic polar solvents favour sn1

A

Polar protic solvents have O–H or N–H bonds and are therefore able to form hydrogen bonds. These solvents solvate the carbocation intermediate, through the formation of ion-dipole forces between the positive carbocation and the partial negative charges on the water molecules (Figure 9). This has the effect of stabilising the carbocation intermediate, which favours the SN1 mechanism.

Dictionary

250
Q

aprotic polar solvents (ethoxyethane, propanne) favour

A

sn2

251
Q

why do aprotic polar solvents (ethoxyethane, propanne) favour sn2

A

These solvents lack O–H or N–H bonds and are not able to form hydrogen bonds. Unlike polar protic solvents, polar aprotic solvents cannot form hydrogen bonds with the nucleophile. This maintains the reactivity of the nucleophile, favouring the SN2 mechanism.

252
Q

factors affecting rate of nucleophilic substitution

A

classification of the halogenoalkane

nature of nucleophile

leaving group

253
Q

why does classification of halogenoalkane affect rate of nucleophilic substiution

A

Tertiary halogenoalkanes react faster via the SN1 mechanism than primary halogenoalkanes do via the SN2 mechanism. The order in terms of rate of reaction (fastest first) is:

254
Q

why does nature of nucleophile affect rate of nucleophilic substiution

A

The effectiveness of a nucleophile depends on its electron density; negatively-charged anions tend to be more reactive than neutral species. This explains why the hydroxide ion is a better nucleophile than a water molecule. The hydroxide ion has a negative charge, whereas the water molecule only has a negative dipole.

Dictionary

255
Q

why does the leaving group affect rate of nucleophilic substitution

A

The iodide ion is the best leaving group of the halide ions. This is due to the relative bond enthalpies: the C–I bond (228 kJ mol−1) is weaker than both the C–Br bond (285 kJ mol−1) and the C–Cl bond (324 kJ mol−1). In terms of rates of reaction, iodoalkanes react faster than bromoalkanes, which react faster than chloroalkanes.

256
Q

what do sn1 reactions start, with and produce

A

SN1 reactions begin with a single enantiomer and result in the production of a racemic mixture containing equal amounts of two enantiomers. A racemic mixture is known as being optically inactive.

257
Q

what do sn2 reactions start with and produce

A

SN2 reactions begin with a single enantiomer and produce only one enantiomer which means that the final product is optically active. Note that optical isomerism is covered in more detail in section 20.3.3.

258
Q

waht undergoes electrophilic addition reactions

A

alkenes

259
Q

during an electrophilic addition reaction what happens

A

During an addition reaction, the weaker pi bond is broken and the atoms that make up the electrophile bond with the two carbon atoms of the double bond.

260
Q

carbon carbond ouble bond

A
261
Q

what is an electrophile

A

an electron-deficient species that is able to accept a pair of electrons from a nucleophile (in this case an alkene), also acting as a Lewis acid

262
Q

stages of electrophilic addition

A
  1. halogen approaches double bond.
  2. the electrons in the halogen molecule that are repelled, creating an indued dipole where the closest atom is positive (electrophilic portion) and othe is nergatice.
  3. at the same time, the pair of electrons that makes up the pi bond move towards the halogen molecule and form a single covalent bond with the nearest halogen atom. This results in the formation of a carbocation intermediate, which causes the bond between the two halogenatoms to break heterolytically, forming an ion.
  4. the halogen ion uses a lone pair ofelectros to form a single covalent bond with the carbocation intermediate.
263
Q

describe electrophilic addition with hydrogen halides

A

These molecules have a permanent bond dipole because of the difference in electronegativity between the halogen and the hydrogen atom. The hydrogen atom has a partial positive charge that is attracted to the electron density of the carbon-carbon double bond. The π electrons of the double bond form a single bond with the hydrogen atom of HBr, which results in the heterolytic fission of the H–Br bond and the formation of a bromide ion. The bromide ion then uses a lone pair of electrons to form a single bond with the carbocation, forming the halogenoalkane bromoethane

264
Q

what re interhalogens

A

compunds composed of two or more different halogen atoms

265
Q

how do you predict the major product

A

use markovnikov’s rule: when hydrogen halides add to asymmetric alkenes, the hydrogen atom bonds to the carbon atom that is already bonded to the greatest number of hydrogen atoms.

this is BECAUSE primary carbocation is the least stable.

266
Q

why is benzene susceptible to attack by electrophiles

A

the delocalised pi system with a region of high electron density. therefore it undergoes electrophilic substitution

267
Q

changes in energy durign electropphilic substitution

A

An important point to note is the increase in energy when the delocalised pi (π) system becomes disrupted; also note the decrease in energy when the π system is reformed in the substituted product. The high activation energy required for the reaction to take place is another testament to the stability of the benzene molecule.

268
Q

how does nitorbenzene form

A

benzene plus conc nitric acid and sulfuric acid (nitrating mixture)

the sulfuritc acid is a catalyst but also is in ther eaction

269
Q

what is the electophile in the nitration of benzene

A

nitronium ion (NO2+)

270
Q

describe the nitration of benzene

A

Benzene reacts with a mixture of concentrated nitric acid and sulfuric acid (known as a nitrating mixture) to form nitrobenzene, C6H5NO2. The electrophile in the reaction is the nitronium ion (NO2+). The nitrating mixture is composed of two concentrated strong acids: sulfuric acid and nitric acid (the sulfuric acid acts as a catalyst for the reaction). Sulfuric acid, being the stronger acid of the two, donates a proton to the nitric acid

The H2NO3+ ion then loses a molecule of water to form the nitronium ion (NO2+)

271
Q

nitration of benzene equation

A

2H2SO4 + HNO3 ⇌ NO2+ + 2HSO4− + H3O+

272
Q

mechansimf ro nitration of benzene

A

A pair of electrons moves from the delocalised pi system to the nitronium ion, represented by the curly arrow. This results in the formation of a bond with the nitronium ion, the formation of a carbocation intermediate and the disruption of the delocalised pi system – note the incomplete circle in the middle of the benzene structure. A pair of electrons from the C–H bond then moves to reform the delocalised pi system, resulting in the loss of a hydrogen ion. This hydrogen ion bonds with the base HSO4− to reform the sulfuric acid catalyst.

273
Q

conditions for ntiration of benzene

A

heat under reflux to 50°C; note that the temperature should not be raised higher than 50°C as further nitration to dinitrobenzene will occur.

274
Q

what are carbonyl compounds

A

Compounds such as aldehydes, ketones and carboxylic acids are known as carbonyl compounds because of the presence of a carbonyl group (C=O).

275
Q

why does the carbonyk group have an effect on polarity

A

the differenece in electronegativity between carbon and oxygen

276
Q

how are carbonyl groups converted back to alcohols

A

reduction reactions.

The partial positive charge on the carbon atom makes this group vulnerable to attack from a nucleophile, which is the hydride ion (H−). The sources of the hydride ions are the reducing agents sodium borohydride (NaBH4) and lithium aluminium hydride (LiAlH4).

277
Q

reduction of an aldehyde to primary alcohol

A

The reducing agent is sodium borohydride (lithium aluminium hydride can also be used) followed by the addition of an acidic solution (H+).

278
Q

reduction of ketone to a secondary alcohol.

A

The reducing agent is sodium borohydride followed by the addition of an acidic solution. As with the reduction of aldehydes, it is also possible to use lithium aluminium hydride as the reducing agent.

279
Q

reduction of carboxylic acids to primary alcohol

A

The reduction of carboxylic acids requires the use of the stronger reducing agent, lithium aluminium hydride (LiAlH4), in dry ether. The reduction reaction first involves the formation of an aldehyde, but because lithium aluminium hydride reacts rapidly with aldehydes, it is not possible to stop the reaction at this point. For this reason, the reaction is shown as proceeding directly from the carboxylic acid to the primary alcohol.

280
Q

what happens in the conversion of nitrobenzene into phenylamine

A

Firstly, nitrobenzene, C6H5NO2, is heated under reflux (using a boiling water bath) together with a mixture of tin (Sn) and concentrated hydrochloric acid. The product, the phenylammonium ion, C6H5NH3+, is protonated as the reaction is carried out under strongly acidic conditions. In the second stage, the phenylammonium ion is deprotonated to produce phenylamine by reacting with sodium hydroxide solution.

281
Q

first stage of the reduction of nitrobenzene

A

nitrobenzene is reacted with tin in an acidic solution to form tin(II) ions, the phenylammonium ion and water. The equation for this reaction is:

C6H5NO2 (l) + 3Sn (s) + 7H+ (aq) → C6H5NH3+ (aq) + 3Sn2+ (aq) + 2H2O (l)

282
Q

second stage of reduction fon itrobenzene

A

the phenylammonium ion is reacted with hydroxide ions to form phenylamine (aniline) and water:

C6H5NH3+ (aq) + OH– (aq) → C6H5NH2 (l) + H2O (l)

283
Q

whats retrosynthesis

A

tarting with the desired product (the target molecule) and working backwards

target molecule ⇒ precursors ⇒ starting materials

284
Q

Which of the following is the intermediate formed during the reduction of nitrobenzene to phenylamine by tin and concentrated hydrochloric acid?

A

the phenylammonium ion

285
Q

what are newman projections

A

represent conformers (conformational isomers)

286
Q

stereoisomers can be divided into

A

configurational isomers and conformational isomers

287
Q

conformatipnal isomers are able to interconvert by rotation around

A

a single bond that is composed fo one sigma bond

288
Q

staggered conformation

A

lower energy conformer

the C–H bonds on the near carbon atom are positioned at angles of 60° relative to the C–H bonds on the far carbon atom.

289
Q

eclipsed conformation

A

the higher energy conformer

the hydrogen atoms on the near carbon atom obscure those atoms on the far carbon atom.

290
Q

if there is a low difference in energy between the two conformers what happens

A

they interconvert readily at room temperature

291
Q

what is torsional strain

A

difference in energy between conformers

292
Q

why do confomrational isomers originate

A

due to the free rotation that takes place around a carbon–carbon single bond, which is composed of one sigma (σ) bond.

293
Q

c double bodns

A

one sigma and one pi

294
Q

cis isomers have higher bp because

A

both halogen atoms on the same side makes it polar

295
Q

higherwhy do trans isomers have lower bp

A

a non-polar molecule as the two chlorine atoms are on opposite sides of the C=C double bond; this cancels out the polarities of the C–Cl bonds. Both molecules will have London dispersion forces of the same strength, but the cis-isomer will have stronger dipole–dipole attractions between the molecules, resulting in a higher boiling point.

296
Q

According to the Cahn–Ingold–Prelog (CIP) priority rules,

A

the atom with the highest atomic number on each carbon atom in the double bond is assigned the highest priority.

297
Q

when does optical isomerim occur

A

in chiral molecules that have a chiral, or asymetric, carbona tom (also known as a chiral centre)

298
Q

asymmetric carbon

A

bonded to four different atoms or groups

299
Q

what are enantiomers

A

optical isomer

300
Q

how many optiacl isomers for a particualr molecule

A

depens on the number of chiral centers in the molecule, generally 2^n

301
Q

A chiral molecule contains an

A

asymmetric carbon atom (sometimes called a chiral carbon atom or a chiral center) that is bonded to four different atoms or groups.

302
Q

enantiomers are mirror iamges so are

A

non-superimposable

303
Q

at does optically active mean

A

rotate the plane of plane-polarised light

304
Q

how is plane polarised light produced

A

when unpolarised light is passed through a polariseing filter

305
Q

what properties are the same for enantiomers

A

same physical and chemical properties

306
Q

hwo is the rotation of the plane of plane polarised light byt he two different enantiomers measured

A

using apolarimeter

307
Q

a poalrimeter consists of

A

a light source, two polarising gilters (one fixed and one rotatable) and a tube that contains a solution of the enantiomer

308
Q

operation of apolarimeter

A

Unpolarised light is passed through a polarising filter, which produces plane-polarised light.

The plane-polarised light passes through a solution of the enantiomer.

An analyser is used to determine the angle of rotation of the plane of the plane-polarised light.

309
Q

two enantiomers can be distinguishe dby the fact that they totate the plane of polane polarised light by

A

equal amount but in opposite directions

310
Q

what is a racemic mixture

A

optially inact ive

equal amounts of enantiomer

311
Q

diastereomers

A

do not have opposite configurations at all of the chiral centres and so are not mirror images of each other

they have opposite configurations at only one of the two chiral centers. Diastereomers can have different physical and chemical properties. Some diastereomers are optically active, but some are not.

IB Chemistry HL (12 decks)

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