10/20 organic chemistry Flashcards
1
Q
empirical formula
A
the formula that gives the simplest whole number ratio of the different types of atom within the compound
2
Q
molecular formula
A
shows the number of each type of atom present. nothing about bonding
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.
4
Q
displayed formula
A
shows all of the atoms and the bonds (represented as lines)
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.
6
Q
alkane suffix
A
-ane
7
Q
alkene suffix
A
-ene
8
Q
alkene suffix
A
-yne
9
Q
alcohol suffix
A
-ol
10
Q
aldehyde suffix
A
-al
11
Q
ketone suffix
A
-one
12
Q
carboxylic acid suffix
A
-oic acid
13
Q
ester suffix
A
-yl -oate
14
Q
1 prefix
A
meth
15
Q
2 prefix
A
eth
16
Q
3 prefix
A
prop
17
Q
4 prefix
A
but
18
Q
5 prefix
A
pent
19
Q
6 prefix
A
hex
20
Q
7 prefix
A
hept
21
Q
8 prefix
A
oct
22
Q
what is the functional group for an alkene
A
a double bond between carbons
23
Q
what is the functional group of halogenoalkane
A
a single bond to a halogen
24
Q
alcohol functional group
A
a single bond to an oxygen and then a single bond to a hydrogen
25
aldehyde functional group
a double bond to a oxygen and a single bond to a hydrogen
26
ketone functional group
a double bond to an oxygen from a carbon
27
carboxylic acid functional group
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
28
nitrile functional group
a triple bond to a nitrogen from a carbon
29
amine functional group
2 single bonds to hydrogens from a nitrogen
30
acyl chloride functional group
a double bond to a oxygen and a single bond to a chlorine all from a carbon. like a ketone and a halogenoalkane
31
acid anhydride functional group
an oxygen is inbetween two carbons. on each of the carbons there is a double bond to an oxygen.
32
ester functional group
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
33
amide functional group
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.
34
what is organic chemistry
the study of carbon compounds
35
what was vitalism
the idea that organic molecules had distincitve chemical properties, making them unique to living organisms.
36
how was vitalism rebuked
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.
37
why do alkanes make good fuels
they react with oxygen in exothermic reactions to produce carbon dioxide and water.
38
as molar mass increases, and the strength of the intermolecular forces between the molecules increase, what happens
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
39
what is a homologous series
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.
40
how many covalent bonds does carbon form
4
41
why is carbon so special as opposed to silicon
although both are in group 14, and so have 4 covalent bonds to make, carbon-hydrogen bonds are stronger than silicon-hydrogen bons
42
addition reaction
reaction where a molecule joins to an unsaturated molecule to produce a saturated molecule
43
aliphatic
organic compounds containing C chains and branches
44
aromatic
organic compounds containing one or more benzene rings
45
carbocation
a positive ion containing one or more benzene rings
46
cyclic
organic compounds containing c rings (not aromatic rings) also called alicyclic
47
dehydrogenation
elimination of hydrogen
48
electrophile
long pair acceptor
49
elimination reaction
reaction where a molecule is lost from a saturated molecule to form an unsaturated molecule
50
free radical
species with an unpaired electron
51
functional group
the atom or group of atoms that is responsible for most of the chemical reactions of a molecule
52
homologous series
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
53
hydrogenation
addition of hydrogen (over heat and a nickel catalyst)?
54
hydroloysis
a reaction involving the breaking of bonds due to reaction with water
55
nucleophile
lone pair doner
56
organic chemistry
study of compounds containing carbon
57
saturated
molecule containing no double bonds
58
sterioisomers
molecules with the same molecular and structural formulae but with different spatial arrangement of atoms
59
geometric isomers
type of stereoisomerism. molecule which have different arrangements of groups around C=C
60
optical isomers
type of stereoisomerism. molecules which are non-superimposable mirror images.
61
structural isomers
molecules with the same molecular formula but different structures
62
chain isomers
type of stereoisomerism. structural isomers that differ by having a different carbon chain
63
position isomers
type of stereoisomerism. structural isomers that differ by having the functional group in a different position
64
functional group isomers
type of stereoisomerism. structural isomers that differ by having a different functional group.
65
substitution reaction
reaction where an atom/group replaces another atom/group
66
unsaturataed
molecule containing double bonds
67
isomers have
the same molecular formula but different displayed formulas
68
types of structural isomerism
chain isomerism
position isomerism
functional group isomerism
69
example of a chain isomer
pentane and 2-methylbutane
70
the greater the number of carbon atoms in the molecular formula
the greater the number of possible isomers
71
examples of positional isomers in C4H8
but-1-ene
but-2-ene
2-methylpropene
72
examples of functional group isomerism
propanal and propanone
73
alkyne suffix
-yne
74
alkyne fucntional group
75
ether prefix
prefix: alkoxy
e. g. methoxy
76
ether functional group
77
arene suffix
benzene
or prefix: phenyl
78
arene functional group
79
what can functional groups be classified as
acidic or basic
80
what do compounds containing a carboxyl functional group do to form the carboxylate ion (R-COO(-))
donate a proton
81
how do amines become a base
using a lone pair of electrons on the nitrogen atom to accept a proton
82
chain isomersim is effectively
changing the carbon skeletons
83
posisitional isomerism is effectively
the position of the functional group moves but NOT the carbon skeleton
84
functional group isomerism
same carbon skeleton but with completely different functional groups or homogolous series
85
types of steroisomers
geometric
optical
86
stereoisomers defintion
molecules with the same structural formula but a different spatial arrangement of atoms
87
structural isomes definition
molecules with the same molecular formula but a different structure
88
volatility is
The measure of how easily a substance evaporates
89
Substances that have stronger intermolecular forces are
less volatile and consequently have higher boiling points.
90
how does increasing molar mass increase boiling point
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.
91
how do branched and chain isomers usually have different boiling points
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
92
how does the functional group change the boiling point
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.
93
what should you do when comparing boiling points of various molecules
try to keep the molar mass the same
94
what does solubuility of molecules depend on
their ability to form hydrogen bonds with water molecules
95
increasing size of the carbon chain, increases the hydrophobic character of the molecule,
decreasing its solubility in polar solvents like water
96
hydrophobic
the non-polar hydrocarbon chain of a molecule which is insoluble in polar solvents such as water.
97
increasing strength of intermolecular force
98
carboxylic acids can form what through hydrogen bonds
dimers, between the two carboxyl groups
99
key organic functional groups
alkanes
alkenes
alcohols
halogenoalkanes
aromatic compounds like benzene
100
what happens due to alkanes having low reactivity
they undergo free radical substitution reactions
101
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...
is an important factor in shaping global policies and economic developments
102
how does methane contribute to greenhouse gas emissions
through agriculture and landfills
103
temperature of thermal cracking
900 celsius
104
temperature of catalytic cracking
450 celsuius
105
atm of thermal cracking
70
106
atm of catalytic cracking
1-2 atm
107
what catalysts are used in thermal cracking
none
108
what catalysts are used in catalytic cracking
zeolites
109
what products are made from thermal cracking
alkenes
110
what products are made from catalytic cracking
motor fuels
aromatic hydrocarbons
cyclic alkanes
branched alkanes
111
where are zeolites found
they are natural occuring and can be manufactured
112
what is an octane ratign
a standard measure of the fuel used in cars and aircraft
113
how is carbon dioxide formed
complete combustion
114
potential problems of carbon dioxide
greenhouse gas causing global warming
115
solutions to reduce carbon dioxide
burn less fossil fuels
116
how is carbon monixde formed
incomplete combustion
117
potential problems of carbon monoxide
toxix
118
ways to reduce carbon monoxide
ensure a good supply of air and oxygen when burning fuel
119
how is carbon fomed
incomplete combustion
120
potential problems with carbon
blackens buildings
global dimming
121
ways to reduce carbon
ensure good supply of air and oxygen when burning fuels
122
how is sulfur dioxide formed
combustion of sulphur in fuel
123
potential problems with sulfur dioxide
acid rain
124
how to reduce sulfur dioxide
remove sulphur before buring or remove so2 after burning (flue gas desulferization)
125
how are nitrogen oxides formed
reaction of N2 in air with O2 at very high temperatures (often in engines or furnaces)
126
problems of nitrogen oxides
acid rain
127
how to reduce nitrogen oxides
for engines, use a catalytic converter
128
how are unburned fuels formed
not all fuel burns
129
potential problems with unburned fuels
wastes fuel, harmful and a greenhouse gas
130
ways to reduce unburned fuel
ensure correct fuel:air mixture when fuel is burned
131
what does acid rain do
damage vegetation
kill fish
damage e.g. limestone
132
flue gas desulphurisation system
133
describe how sun enters and exits the earths atmosphere
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
longer chain lengths...
increase boiling point
135
branched isomers...
have lower boiling points
136
boiling points of the alkanes
-162 (methane) to 36 (pentane)
137
boiling points of methylalkanes
-12 (methylpropane) and 28 (methylbutane)
138
why do longer carbon chains have higher boiling points
stronger van der Waal's forces between molecuels (more electrons in the molecules)
139
why do branched isomers have lower boiling points
weaker van der Waals forces between molecules (due to moelcules not being able to pack as close together)
140
basic idea of fractional distillation
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
fraction definition
a mixture of hydrocarbosn with similar boiling points
142
as carbon chain gets longer, the hydrocarbons:
become more viscous
harder to ignite
less volatile
have higher boiling points
143
what is cracking
thermal decomposition of alkanes
144
complete combustion equation
alkane + oxygen --\> carbon dioxide + water
145
incomplete combustion equation
alkane + oxygen --\> carbon + water
146
how can impurities containing sulfur be removed
using afurnace by flue gas desulferisation
147
give the equation for how gases pass through a scrubber containing calcium oxide or calcium carbonate which reacts with the sulfur dioxide
CaO + SO2 --\> CaSO3
or
CaCO3 + SO2 --\> CaSO3 + SO2
148
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
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
what do catalytic converters do
remove CO, NOx, and unburned hydrocarbons from exhaust gases, making them CO2, N2 and H2O
150
what do catalytic convertes have to make them have a large surface area
a ceramic honeycomb coated with a thin layer of catalyst metals (Pt, Pd, Rh)
151
briefly explain global warming
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
what are haloalkanes
saturated molecueles made of carbon and hydrogen and halogens
153
alkane + hydrogen --\>
haloalkane + hydrogen halide
154
traces of products from further subsititution in the methane + chlorine --\> chloromethane + hydrogen chloride reaction
CH2Cl2
CHCl3
CCl4
C2H6
155
stages of free radical substitution
inititation
propogation
termination
156
what do arrows show in org chem
electrons movement
157
initiation
158
propogation
159
termination
160
what is the first step for propogation
beginning reactant + free radical halogen --\> halogen halide + beginning reactant free radical (one less hydrogen)
161
what is the second step for propogation
the beginning reactant free radical + halogen molecule --\> ending product + halogen free radical
162
what is the UV light for
to break the single covalent bond of the halogen
163
properties of small alkanes
low boiling points
runny
easy to ignite
burns with clean flame
164
properties of big alkanes
high boiling points
viscous
hard to ignite
burns with smoky flame
165
what increases from small to big alkanes
boiling points
viscosity
flammability
flame gets dirtiers
166
for what fractions is demand higher than supply
petrol and disel
NOT kerosene or fuel oil
167
cracking image
168
conditions required for crackung
aluminium oxide catalyst AND high temperatures of 600-700 celsius
169
test for alkanes/akenes
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
vegetable oils + ??? ---\> shortening/margarine
H2 over heat, nickel catalyst
171
saturated fatty acids have
carbon carbons single bonds
172
unsaturated fatty acids have
carbon carbond double bond
173
trans fatty acids have
hydrogen bonds on opposite sides of the chain of carbon-carbon single bonds
174
what reaction do alkenes undergo
addition reactions, small molecules add across the C=C
175
what type of double bond do alkenes contain
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
what do electrophiles do
add across the double bond to form new, saturated products with the pi-bond of the alkene being broken in the process.
177
stages of alkene addition reaction (electrophilic addition)
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
priamry, secondary, tertiary carbocation
179
what is markonikov's rule
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
what is the least stable carbocation
primary carbocation. secondary and tertairy increase alongside stability.
181
carbocation stability increases with the number of attatched...
alkyl groups
182
When hydrogen halides undergo reactions with an asymmetric alkene, there are
two possible products, depending on which carbon atom in the double bond the hydrogen atom bonds with.
183
polymer def
long chain molecule made from lots of small molecules joined together
184
monomer def
small molecules that join together to make polymers
185
addition polymerisation def
formation of long chain molecules from lots of small molecules joining together with no other products
186
which structure has brackets and an n
the polymer structure
NOT the repeating unit
187
low density poly(ethene)
molecules loosely packed due to branching
flexible and soft
bags, cling film
188
high density poly(ethene)
molecules tightly packed
stiffer and harder
buckets, bottles
189
uses of ethene
LPDE
HPDE
190
uses of methylethene
plastic bottles
191
uses of phenylethene
packaging
crates/ropes
192
uses of chloroethene
pipes
window frames
193
uses of tetrafluroethene
non stick pans
194
uses of methyl 2-cyanopropenoate
adhesives/super glue
195
uses of methyl 2-methyl propenaoate
glass substitute windows/rulers
196
common everyday name for methylethene
polypropylene
197
common everyday name for phenylethene
polystyrene
198
common everyday name for chloroethene
PVC
199
common everyday name for tetrafluroethene
PTFE/teflon
200
common everyday name for methyl-2-cyanopropenoate
super glue
201
common everyday name for methyl-2-methylpropenoate
PMMA/perspex
202
what happens when you mix water and ethanol
initally, a cloudy mixture is formed. then it becomes clearless because they are miscible liquids
203
what happens when you mix ethanol and a rice grain sized of sodium
small bubbles of hydrogen gas
204
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
green --\> grey. shows oxidation has occured.
205
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
green--\> grey. this shows oxidation has occured.
206
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
nothing. methylpropan-2-ol and other tertiary carbocations cannot oxidise alcohols.
207
what happens in tollens reagent
when silver nitrate and ammonium hydroxide are mixed until silver oxide precipitate just dissolves, and an aldehyde is added.
greyish precipitate
208
what happens in tollens reagent
when silver nitrate and ammonium hydroxide are mixed until silver oxide precipitate just dissolves, and a ketone is added.
no reaction
209
what happens in fehling's solution
Fehling's A and Fehling's B are mixed with a few drops of aldehyde
a deep blue colour with a precipitate ont op
210
what happens in fehling's solution
Fehling's A and Fehling's B are mixed with a few drops of ketone
no reaction
211
primary alchols have
one R group on the carbon attatched to the OH group
212
secondary alcohols have
two R groups on the carbon attatched to the OH group
213
tertiary alcohols have
three R group on the carbon attatched to the OH group
214
solubility in water ________ decreases with increasing size of hydrocarbon chain e.g. pentanol and hexanol are not particularly soluble in water.
decreases
215
oxidation of alcohols
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
what is the oxidising agent for alcohols
heated acidified potassium dichromate
217
what is the colour change of dichromate when heated and acidified
orange to green
218
what is the equation for when chromate is heated and acidified
Cr2O7^2- --\> Cr^3+
219
stages of primary alchols when oxidised
alcohol
aldehyde
carboxylic acid
220
stages of secondary alchols when oxidised
alcohol
ketone
no reacton
221
stages of tertiary alcohols when oxidised
222
what is the colour change for potassium manganate when heated
from purple to a very pale pink
223
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.
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
what are esters derived from
carboxylic acids
225
applications of esters
flavouring agents and medications and solvents and explosives
226
what is esterification
a reversible reaction where a carboxylic acid and an alcohol are heated in the presence of a catalyst, normally concentrated sulfuric acid.
227
what are the wavelengths of visible light range
400-700 nm
228
carboxylic acids + alcohols (with concentrated H2SO4 catalyst) makes...
esters
229
are esterification reacations reversible
most are
230
because H2O is formed, what else can esterification reactions be described as
condensation
231
what is the reverse reaction of an esterfication called
hydrolysis
232
what is the role of suphuric acid in esterifications
catalyses the reaction
233
why is the sodium carbonate used to pour the esters into in esterifcations
neutralises the sulphuric acid and stops the reaction
234
what pieces of evidence shows the Keuk;e structure was wrong
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
what reactions does benzene readily undergo
combustion
substitution
236
why does benzene undergo electrophilic substitution reactions
because electrophiles are attracted to regions of negative charge such as the electron-rich benzene ring.
237
what is an electrophilic reaction
replacement of a hydrogen atom with an electrophile.
238
what is the backside attack realted to
sn2
239
what is the backside attack
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
what occurs at the same time as the attack of the nucelophile
the departure of the halide
241
stages of an sn2 reaction
242
difference in sn2 and sn1
in sn1 the loss of the halide occurs ebfore the addtion fo the nculeophile.
in sn2 they cocur at the same time
243
what does the rate of reaction of the sn2 reaction depend on
concentration of both the alkyl halide and the nuclophile
244
stages of the sn1 reaction
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
what is steric hindrance
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
how is the carbocation stablised in sn1 reactions
by each of the buljky methyl froups having an electron donating effect (or psotiive inductive effect)
247
incresing carbocation stability
primary
secondary
tertiary
248
protic polar solvents (ethanol, ammonia, water) faavour which type of reaction
sn1
249
why do protic polar solvents favour sn1
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
aprotic polar solvents (ethoxyethane, propanne) favour
sn2
251
why do aprotic polar solvents (ethoxyethane, propanne) favour sn2
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
factors affecting rate of nucleophilic substitution
classification of the halogenoalkane
nature of nucleophile
leaving group
253
why does classification of halogenoalkane affect rate of nucleophilic substiution
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
why does nature of nucleophile affect rate of nucleophilic substiution
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
why does the leaving group affect rate of nucleophilic substitution
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
what do sn1 reactions start, with and produce
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
what do sn2 reactions start with and produce
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_](https://app.kognity.com/study/app/u6ib4-chemistry/sid-48-cid-139981/book/optical-isomerism-id-7066/).
258
waht undergoes electrophilic addition reactions
alkenes
259
during an electrophilic addition reaction what happens
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
carbon carbond ouble bond
261
what is an electrophile
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
stages of electrophilic addition
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
describe electrophilic addition with hydrogen halides
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
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what re interhalogens
compunds composed of two or more different halogen atoms
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how do you predict the major product
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.
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why is benzene susceptible to attack by electrophiles
the delocalised pi system with a region of high electron density. therefore it undergoes electrophilic substitution
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changes in energy durign electropphilic substitution
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.
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how does nitorbenzene form
benzene plus conc nitric acid and sulfuric acid (nitrating mixture)
the sulfuritc acid is a catalyst but also is in ther eaction
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what is the electophile in the nitration of benzene
nitronium ion (NO2+)
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describe the nitration of benzene
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+)
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nitration of benzene equation
2H2SO4 + HNO3 ⇌ NO2+ + 2HSO4− + H3O+
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mechansimf ro nitration of benzene
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.
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conditions for ntiration of benzene
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.
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what are carbonyl compounds
Compounds such as aldehydes, ketones and carboxylic acids are known as **carbonyl compounds** because of the presence of a carbonyl group (C=O).
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why does the carbonyk group have an effect on polarity
the differenece in electronegativity between carbon and oxygen
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how are carbonyl groups converted back to alcohols
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).
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reduction of an aldehyde to primary alcohol
The reducing agent is sodium borohydride (lithium aluminium hydride can also be used) followed by the addition of an acidic solution (H+).
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reduction of ketone to a secondary alcohol.
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.
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reduction of carboxylic acids to primary alcohol
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.
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what happens in the conversion of nitrobenzene into phenylamine
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.
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first stage of the reduction of nitrobenzene
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)
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second stage of reduction fon itrobenzene
the phenylammonium ion is reacted with hydroxide ions to form phenylamine (aniline) and water:
C6H5NH3+ (aq) + OH– (aq) → C6H5NH2 (l) + H2O (l)
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whats retrosynthesis
tarting with the desired product (the **target molecule**) and working backwards
target molecule ⇒ precursors ⇒ starting materials
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Which of the following is the intermediate formed during the reduction of nitrobenzene to phenylamine by tin and concentrated hydrochloric acid?
the phenylammonium ion
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what are newman projections
represent conformers (conformational isomers)
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stereoisomers can be divided into
configurational isomers and conformational isomers
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conformatipnal isomers are able to interconvert by rotation around
a single bond that is composed fo one sigma bond
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staggered conformation
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.
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eclipsed conformation
the higher energy conformer
the hydrogen atoms on the near carbon atom obscure those atoms on the far carbon atom.
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if there is a low difference in energy between the two conformers what happens
they interconvert readily at room temperature
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what is torsional strain
difference in energy between conformers
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why do confomrational isomers originate
due to the free rotation that takes place around a carbon–carbon single bond, which is composed of one sigma (σ) bond.
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c double bodns
one sigma and one pi
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cis isomers have higher bp because
both halogen atoms on the same side makes it polar
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higherwhy do trans isomers have lower bp
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.
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According to the Cahn–Ingold–Prelog (CIP) priority rules,
the atom with the highest atomic number on each carbon atom in the double bond is assigned the highest priority.
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when does optical isomerim occur
in chiral molecules that have a chiral, or asymetric, carbona tom (also known as a chiral centre)
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asymmetric carbon
bonded to four different atoms or groups
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what are enantiomers
optical isomer
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how many optiacl isomers for a particualr molecule
depens on the number of chiral centers in the molecule, generally 2^n
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A chiral molecule contains an
asymmetric carbon atom (sometimes called a chiral carbon atom or a chiral center) that is bonded to four different atoms or groups.
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enantiomers are mirror iamges so are
non-superimposable
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at does optically active mean
rotate the plane of plane-polarised light
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how is plane polarised light produced
when unpolarised light is passed through a polariseing filter
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what properties are the same for enantiomers
same physical and chemical properties
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hwo is the rotation of the plane of plane polarised light byt he two different enantiomers measured
using apolarimeter
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a poalrimeter consists of
a light source, two polarising gilters (one fixed and one rotatable) and a tube that contains a solution of the enantiomer
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operation of apolarimeter
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.
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two enantiomers can be distinguishe dby the fact that they totate the plane of polane polarised light by
equal amount but in opposite directions
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what is a racemic mixture
optially inact ive
equal amounts of enantiomer
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diastereomers
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.
