Organic Flashcards
(110 cards)
1
Q
Why does Br2 react more readily with alkenes than benzene?
A
-pi bond in alkane has localised e‐ above and below plane of the C=C
- increases e- density and induces dipole in Br2 to act as electrophile
- benzene has delocalise e- above and below C ring and e- density is less that C=C
- not enough density to polarise the bromine to act as an electrophile
2
Q
What is benzene’s bond angle and the bond lengths compared to a single and double covalent bond?
A
-benzene is planar with bond abgle of 120⁰
-all bond lengths are equal
- bond lengths are smaller than single C-C bonds but longer than C=C bonds
3
Q
What are the reagents for reducing nitrobenzene to aminobenzene?
A
- Sn and conc. HCl under reflux forms a phenyl ammonium ion
-add NaOH
4
Q
What forms when an acyl chloride reacts with water?
A
- a carboxylic acid + HCl
- vigorous reaction and white misty fumes of HCl gas produced
5
Q
What does the Bromination of benzene require?
A
A halogen carrier (AlBr3)
6
Q
Why does cyclohexene not require a halogen carrier when undergoing bromination?
A
-in alkenes the pi electrons are concentrated between the two carbons
- electronic density is high enough for electrophiles to be attracted to alkenes
7
Q
Describe the formation of 2-nitrophenol
A
Phenol + dilute nitric acid at RTP
8
Q
Why does phenol act as a weak acid?
A
-When phenol dissociates, a phenoxide ion forms and H+ forms
- due to the high electronegativity of the oxygen on the phenoxide, demoralised electrons are drawn towards it
- causes a high charge around the oxygen and attracts H+ back again
- equilibrium is to the LEFT
9
Q
How do you reduce aldehydes and ketones to alcohols
A
Aqueous Sodium borahydride (NaBH4) and H+
10
Q
Why might you expect compounds with similar Mr values to have similar boiling points?
A
They will have a similar amount of London forces between molecules
11
Q
What is the colour change when KMnO4 is added to an aldehyde?
A
Purple to colourless
12
Q
Why is HCN not used to provide the CN- nucleophile?
A
- HCN is a highly toxic gas and difficult to store
-KCN is a white solid= dissolve in water with small vol. of sulfuric acid to form CN-
13
Q
In terms of rates of reaction, why is KCN a better reagent than HCN when lengthening a carbon chain?
A
- HCN is a weak acid so does not fully dissociate into H+ and CN- ions
- rate pf reaction is slower with HCN as KCN fully dissociates
14
Q
Why does optical isomerism occur in the products formed when reacting aldehydes with CN-?
A
- the C=O bond is planar so the CN- can attack from either side
- this causes the optical isomers
15
Q
What is needed in excess to form a secondary amine and why?
A
- excess primary amine with RX
- ensures there is sufficient primary amine to attack the remaining haloalkanes
-ensures no further substitution takes place
16
Q
Why can amines act as Bronsted Lowry Bases?
A
- there is a lone pair on the N atom
- it can accept a proton
- forms a dative bond
17
Q
Why are polyesters more reactive than addition polymers?
A
-Molecules in addition polymers are fully saturated so they are non-polar (the molecules are chemically inert)
-Polyesters contain polar bonds so are able to react with more (acids/ alkalis/ nucleophiles)
18
Q
How does the reactivity of polymers affect their biodegradability?
A
-polyalkenes are non-biodegradable because they are fully saturated / they are chemically inert
-polyamides and polyesters have polar bonds so are able to react with nucleophiles etc
19
Q
Define molecular formula
A
The actual number of atoms in a molecule or element
20
Q
Define structural formula
A
arrangement of atoms in a molecule without showing all the bonds
20
Q
Define empirical formula
A
Simplest whole number ratio of atoms in a compound
21
Q
Define skeletal formula
A
Show the bonds of the carbon skeleton only (H and C atoms not shown but functional groups are)
22
Q
Define displayed formula
A
Show the arrangement of atoms showing all bonds and atoms in the molecule
23
Q
Define a homologous series
A
- a group of compounds that contain the same functional groups and have the same general formula
- successive members in same homologous series differe by CH2
24
What are aromatic compounds?
Compounds that contain a benzene ring which may have different functional/alkyl groups coming from this
25
What are alicyclic compounds?
Rings that aren't aromatic (have same general formula as alkenes)
26
What are aliphatic compounds?
Straight, branched or non aromatic chains
27
What are the 2 types of bond fission?
1. heterolytic fission= bond breaks and electrons are distributed unequally to form 2 different ions **double headed arrow shows movement of a pair of electrons**
2. homolytic fission= bond breaks and pair of electrons shared equally to form 2 uncharged radicals
**dot shows unpaired electron on atom**
28
Define structural isomerism
the isomers have same molecular formula but different structural formulae
29
What are the 3 types of structural isomerism?
1. chain isomerism= same molecular formula but _different arangement of carbon skeleton_
2. positional isomerism= same molecular formula but _different position of functional group on carbon skeleton_
3. functional group isomerism= same molecular formula but _different fuctional group_
30
Describe the shape of alkane molecules
- always from tetrahedral shape around carbon atom (angle around each bond is 109.5)
- bonds repel eachother equally as bonds contain electrons so will want to be as far apart as possible
31
How does branching and length of chain affect bp?
- no branching means molecules can pack together closely = _more surface contact_ = higher bp ac induced dipole-dipoles between molecules are stronger
- longer, straight chained hydrocarbons have more London forces so more energy needed to over come forces= bp increases
- branched hydrocarbons can't pack together as closely which weakens London forces
**Bigger molecules or atoms have more London forces due to larger electron clouds**
32
Describe free radical substitution reactions
1. Initiation= radicals produced by visible light/UV light and bond breaks via homolytic fission (2 radicals)
2. Propogation= radical reacts with non-radical and new radicals are created which can also react with non-radical molecules **chain reaction**
3. Termination= when 2 radicals react and form a non-radical molecule which ends chain reaction
33
Describe the chlorination of methane to form chloromethane
1. Initiation= sunlight (UV) breaks Cl-Cl bond by _photodissociation_ and bond breakes homolytically and produces 2 highly reactive Cl*
2. Propogation= Cl* reacts with methane to form CH3* + HCl
- CH3* then reacts with Cl2 to form chloromethane and Cl*
- the Cl* can react with more methane
3. Termination= Cl* can react with CH3* to form chloromethane and other radicals react with eachother etc.
34
Why is it difficult to produce just chloromethane during free radical substitution?
1. excess Chlorine:
- we will get di, tri and tetra haloalkane which all ahve to be separated
2. excess methane:
- we will reduce amount of multiple substitutions as there is a greater chance for chlorine reacting with methane
- **isomers also form because free radical substituion can occur anywhere on a hydrocarbon**
35
Describe sigma bonds
1. sigma bonds form when 2 s orbitals overlap and align horizontally to give a siongle convalent bond
2. strong electrostatic attraction between nuclei and shared pair of electrons due to _high electron density between nuclei_= high bond enthalpy and strongest type of bond
36
Describe pi bonds
- parallel overlap of 2 p-orbitals which have a dumbell shape= when they merge they form oblong shapes (one above and below bond)
- pi bonds weaker than sigma bonds as electron density spread out above and below nuclei (lower bond enthalpy due to decreased electrostatic attraction)
37
What does a double bond contain and why does it make alkenes so reactive?
- a sigma and pi bond
- high electron density as four electrons are shared in double bond (very reactive)
- open to attack from electrophiles = _pi bond sticks out and whole double bond has high electron density_
- pi bond has low bond enthalpy so alkenes are reactive
38
Define steroisomerism
- same structural formula but different arrangement of atoms in space
- e.g E/Z isomerism
39
Define electrophiles and nucleophiles
- electrophile= electron pair acceptor as they are electron deficient
- nucleophile= electron donator as they are negatively charged species
40
Why are alkanes not as reactive as alkenes?
- alkanes only have sigma bonds and they are not polar so are not as reactive as alkenes which have both sigma and pi bonds
41
What determines the amount of products that will form from unsymmetrical alkenes when reacting with HX?
- determined by stability of carbocation intermediate
- more alkyl groups bonded to carbocation, the more stable it is
- this is because alkyl groups push electrons twoard positive carbocation and stabilise it
PRIMARY= 1 R group
SECONDARY= 2 R groups
TERTIARY=3 R groups (major)
42
Describe Markownikoff's rule
- the major prodcut when we add a hydrogen halide to an unsymmetrical alkene is where the H adds to carbon with most number of hydrogens already
43
What are the benefits and disadvantages of landfills to dispose of poymers (plastics)?
_:)_
- useful for plastics that are difficult to recycle
- too difficult to separate from other materials
_:(_
- landfill is not very sustainable as large amounts of land is needed (deforestation)
- increasingly expensive to use land for waste disposal
44
Whys recycling plastics good?
- most plastics made from non-renewable crude oil so recycling reduces dependency on crude oil
- other plastics can be cracked into monomers which can be used as an _organic feedstock_ for plastics
45
What are the advantages and disadvantages of buring plastic waste?
- incineration can be used on plastics that can't be recycled and the buring can generate electricity
- burning plastic can release toxic fumes which need to be monitored (especially chlorine based PVC which can produce HCl)
46
Describe biodegradable polymers
- polymers that decompose under certain conditions (supply of O2 and moisture) by microorganisms
- made from both oil fractions and renewable resources (starch) **:( more expensive tho**
- photodegradable polymers degrade when exposed to light
**good because lowers the need to use finite resources and less need to use landfill etc.**
47
Describe the solubility of alcohols
- the OH bond is polar so electrons are drawn to the more electronegative O in the covalent bond
- this means alcohols form H bonds with water as the delta+ of the H on water are attracted to the O (dissolve)
- **doesn't apply to longer chained alcohols because longer = more insoluble as the carbon chain is non-polar so reduces the interactions water can amke with the alcohol**
48
Why are alcohols less volatile than alkanes?
- can H bond to eachother and H bonds are strongest intermolecular force (alcohols have higher boiling points as have H bonds AND London forces)
49
What happens when non-primary alcohols are dehydrated?
- can get different positional isomers of alkenes and may also get E/Z isomers
- **3 different alkenes may form**
50
Describe halogen reactivity
- become more reactive down group and hydrolyse fastes
- bond strength/enthalpy determines reactivity of haloalkanes NOT POLARITY
-
51
What are CFCs?
- ChloroFluoroCarbons
- break down ozone (O3) in atmosphere
- stable molecules that break down by UV radiation and radicals catalyse the break down of ozone
- C-Cl bonds broken easiest by UV as have lowest bond enthalpy
52
Describe the action of CFCs
1. initiation= sunlight breaks C-Cl bond and produces 2 radicals (FCl2C* + Cl*
2. propogation= Cl* reacts with O3 to form ClO* and O2
- ClO* reacts more with O3 to form O2 and Cl* (reforms as it acts as a catalyst)
3. Termination= 2 radicals react to form non-radical like Cl2
**overall: 2O3 --> 3O2**
53
Describe the destruction of ozone by NO2
**NO2 + sunlight--> NO* + O2**
1. R* + O3--> O2 + RO*
2. RO* + O --> O2 + R* (R* reformed as it acts as catlyst)
54
Why are CFCs restricted now?
- stable, unreactive non-toxic chemicals that were used in fridges as refrigerant and propellant in deoderants
- damge ozone layer and ozone absorbs harmful UV radiation that cause skin cancer
55
What is the alternative to CFCs?
- HFcs that don't contain chlorine so no chlorine radicals are formed to deplete ozone
- industrial fridges use ammonia as refrigerant now
56
Describe Global warming
- electromagnetic radiation from the sun reached eart and is absorbed by land and sea
- some of the radiation is re-emitted as infrared
- greenhouse gases absorb this radiation and re-emit this back to Earth (greenhouse gas effect) **convalent bonds absorb radiation**
57
How does infrared spectroscopy work?
- uses IR to increase the vibrational energy of covalent bonds in a sample
- the frequency of IR absorbed by covalent bond is detected
58
What does the frequency of infrared radiation absorbed by a covalent bond depend on?
1. the atoms that are either side of a bond
2. the position of the bond in the molecule (O-H in carboxylic acid/ alcohol
59
How is IR spectroscopy used in breathalysers?
- measures amount of ethanol in a sample of breath
- on IR spectru, it measures intensity of C-H peak NOT O-H peak as water is also found in breath
60
How is IR spectroscopy used in emissions testing?
- IR can be used to test car emissions during MOT
- peaks can show levels of nitrogen monoxide and CO
61
What is m/z?
- mass of a fragment divided by charge (as most have =1, normally same as fragment mass)
62
What is the M+1 peak?
- last peak/ molecular ion peak which is caused by the presence of Carbon 13
63
Describe refluxing
- used when you want to heat volatrile liquids and prevents any loss of them as gases
1. Liebig condenser set up vertically with round bottom flask attached
2. voltaile compounds evaporate and condese and fall back into flask
3. **use a water bath/mantle for flammable liquids**
64
Describe distillation
- used when we want to separate substances with different boiling points
1. if compound has lower bp, hear starting mixture to to bp so compound is separated into separate vessel
2. if compound has higher bp than starting material, heat to bp and compound remains in round bottom flask
**useful when you want to extract a chemical before it reacts any further**
65
Describe redistillation and separation (preparation of organic liquid)
- when we want to purify colatile substances which can be purified further using separation
- separation used to remove impurities dissolved in water:
1. add products from distillation into separating funnel and add water to dissolve soluble impurites (creates aq solution)
2. allow to settle and 2 layers form (top= impure product + bottom= aq layer containing water soluble impurities)
3. drain aq layer off abd take impure product from separating funnel into round bottomed flask
4. add anhydrough CaCl2 (dehydrating agen) and will remove aqueous substances still remaining
**INVERT flask and leave for 20-30 minutes**
66
Describe the purification of an organic solid (recrystallisation)
1. add _minimum_ amount of hot solvent (minimum avoids loss of product and the solid must be soluble in hot but insoluble in cold solvent)
2. After this dissolves organic solid and impurities, leave to cool slowly = crystals of product form and impurities stay in solvent
3. crystals removed by pressure filtration (Buchner funnel and sidearm flask with vacuum line) and wash wi/ ice cold solvent
4. dry
67
Why do impurities not form crystals when the organic solid is purified?
- present in very small amounts so would take a long time to crystallise
68
Describe benzene's structure
- 4 valent electrons and each carbon bonded to 2 other carbons and 1 H atom
- final electron is in a p-orbital whcih sticks out above and below planar ring
- all C-C bonds in molecule are same (saame bond length)= due to _delocalised e- structure_
- lone electrons in the p-orbitals overlap to form delocalised pi system (ring od delocalised e-)
- bond length is longer than single bond and shorter than double bond
68
How does melting point + boiling point show purity?
- if impure, teh mp will be lower and the bp will be higher
- if very impure, the mp and bp will occur across wide range
69
Describe Kekule's structure of benzene
- alternating double and single bonds where no delocalised electrons
- cyclahexa-1.3.5-triene
70
Why is Kekule's theoretical model of benzene incorrect?
- difference in enthalpy change of hydrogenation of benzene and cyclohexa-1.3.5-triene
- per double bond, hydrogenation enthalpy change would be -120kJmol-1
- if 3, thene benzene should have -360kJmol-1 but it actually is less exothermic (-208kJmol-1)
**benzene is more stable than theoretical structure due to delocalised electron structure**
71
What arenes do we name with benzene at the end?
- bromobenzene (halogens attached)
- methyl benzenes etc.
- nitrobenzene (NO2)
72
What reactions doe arenes undergo and why?
- high e- density so attractive to attack from electrophiles
- DON't undergo electrophilic addition as this would disrupt stable ring of electrons
- electrophlic substitution takes place instead
73
Why must a halogen carrier be used when undergoing Friedel-Crafts Acylation?
- acyl chloride must react with halogen carrier to create a strongly positive electrophile
- acyl groups are not positive enough to be added to benzene
- halogen carrier accepts a pair of electrons away from acyl group to form carbocation (**strong electrophile produced**)
74
Why is phenol more reactive than benzene?
- due to higher electron density in the ring
- electrophilic substitution reactions more likely as the electrons in p-orbital of the O overlap with the delocalised ring structure (partly delocalised into pi system)
75
How do electron withdrawing groups on a benzene ring affect reactivity of carbons in the ring?
- affect substitution reactions on carbons 3 + 5
- due to electronegative gruop withdrawing e- density from carbons 2,4 + 6 _so electrophiles more likely to attack 3 + 5 and substitute_
**e.g NO2+**
76
How do electron donating groups on benzene affect reacivity of carbons in benzene ring?
- affect substitution on carbons 2, 4 and 6
- electron dontaing groups donate e- and increase density in ring, specifically to carbon 2,4 + 6 _electrophiles more likely to attack carbons 2,4 and 6_
**e.g NH2 and OH**
77
What is Tollen's reagent?
- contains [Ag(NH3)2]+ and is added to warm aldehyde/ketone
- in aldehydes _reduced to silver which coats inside of flask_
- in ketones _no silver ppt formed_
**warm the flask in water bath, not using Bunsen as aldehydes/ketones are flammable**
78
How would you make Tollen's reagent?
- add NaOH to silver nitrate (colourless) which forms brown ppt
- add a few drops of dlute ammonia until ppt dissolves
79
What is 2,4DNP(Brady's Reagent)?
- if carbonyl present= bright ornage ppt
- the ppt is a derivative of the carbonyl compound so will have different melting points which can be compared using data bases to find what carbonyl present
80
Describe the mechanism of tyhe reduction of aldehydes/ketones
- hydride ions from NaBH4 reduces aldehydes/ketones to alcohols
- nucleophilic addition
- H- attacks delta + carbon and double bond removed
- negative oxygen then has its lone pair move to H+ which is from the acid/water present
81
Describe the reaction between KCN and carbonyls
- KCN dissociates into K+ and CN- when dissolved in acidic solution
- CN- is nucleophile and attcks delta+ C
- negative O then bonds with H+
- forms hydroxynitrile
**HCN can be used but no acid needed as H+ will be present from its dissociation**
82
When reacting unsymmetrical ketones/aldehydes with KCN, what happens?
- a mixture of enantiomers porduced due to optical isomerism and CN- can attack from either side
83
Describe how COOHs are weak acids
- partially dissociate into H+ and carboxylate ion (equilibrium lies to L)
- reacts with _carbonates_ to form salt, CO2 and water
- react with _alkalis_ to form salt and water
84
How are acyl chlorides formed?
- COOH + thionyl chloride(SOCl2)
- products are acyl chloride + SO2 and HCl
85
Describe how amines act as bases
- amines have a lone pair of electrons allowing them to accept a proton
- H+ bonds via dative covalent bond (both electrons in bond originate from the lone pair on N)
**strength of base determined by higher electron density= e- more readily available**
- therefore, more alkyl groups= increased e- density of lone pair on N due to alkyl groups pushing e- onto N
- _aromatic amine->tertiary in basicity_
86
Why are aromatic amines weak bases?
- due to lone pair on N partially delocalising into benzene ring
- this decreases electron density of lone pair (less readily available to accept H+)
87
Describe the preparation of primary amines w/ haloalkanes and what is it's disadvantage?
- excess ethanolic NH3 + halogenalkane --> primary amine + NH4Cl (ammonium chloride salt)
- primaru amines still have lone pair so can act as a nucleophile and react with remaining haloalkanes
- **produces secondary, tertiary and quaternary salts too = impure product**
88
How are aromatic amines made?
- reducing nitrocompounds like nitrobenzen
1. nitrobenzene under reflux with Conc HCl + Sn catalyst --> salt C6H5NH3Cl
- then NaOH produces aromatic amine (phenyl amine)
89
Define amphoteric
- molecules that have acidic AND basic properties
90
Give the properties of amino acids
1. amphoteric due to acidic COOH and basic NH2
2. organic side chain represented by R (glycine doesn't and just has hydrogen)
3. chiral molecules as they have 4 differetn groups around a central carbon (they rotate plane polarised light) **except glycine**
91
Define optical isomerism
- type of steroisomerism, where optical isomers have same structural formula bit different arrangement of atoms in space
- mirror images of eachother and have a chiral carbon
92
What are enatiomers?
- as a chiral carbon has 4 different groups attached, we can arrange the groups in 2 ways= 2 different enantiomers
- they are non-superimposable mirror images of eachother (won't overlap)
93
Define condensation polymers
- where 2 different monomers with at least 2 different functional groups react = link is made and water eliminated
- the link determines what polymer is produced (polyamides/polyesters)
94
How are polyamides formed?
- react dicarboxylic acids + diamines together
- amide links form (O=C-NH)
- 2n water produced
95
How are polyesters formed?
- react dicarboxylic acids and diols together
- ester links formed (O=C-O)
- 2n of water produced
96
Describe hydrolysis of condesation polymers
- 2n water produces orignal monomers
-
97
How are nitriles used to make amines?
- reaction is called catalytic hydrogenation (reduction of nitriles)
- this reaction forms only oure product, unlike with haloalkanes
- **H2 + Ni + high temp and pressure**
- _or can use strng reducing agent LIAlH4 and dilute acid_ but this is more expensive
98
Describe the hydrolysing of nitriles and hydroxynitriles
1. nitrile + 2H2O + HCl --> carboxylic acid + NH4Cl (ammonium salt)
2. hydroxynitrile + 2H2O + HCl --> hydroxycarboxylic acid + NH4 Cl
99
How would you measure exact melting points?
1. add sample of solid to capillary tube (tapping it so it sits at the bottom) and place tube into beaker of oil w/ thermometer
2. slowly increase temperature until substance starts to melt and record temperature (also record temperature at whcih it fully melts)
3. compare melting point with data book values
**if impurities, mp will be lower and temp range substance melts at will be larger**
100
Describe the tests for phenol
1. react with strong bases like NaOH and _solid dissolves to form colourless salt_
2. react w/ weaker bases like a carbonate as above test doesn't conclude its a phenol
- carbonates will only react w/ strong acids so if phenol presnt (no efforvesence)
101
Describe the test for COOH
- react w/ carbonate (Na2CO3)
- make CO2 gas and water (bubble through lime water=cloudy)
- **use a flask with tube attached to test tube with limewater and bung on top**
102
Describe thin layer chromatography
1. use stationary phase of silica mounted on a glass plate and draw pencil line and drops of mixture
2. place plate in solvent and the base line must be above solvent level
3. leave until solvent moves up near top of plate, remove and mark _solvent front_ and allow to dry
4. left w/chromatogram and identify chemicals present in mixture by comparing Rf values
**Rf= distance travelled by spot/distance by solvent**
103
How does TLC work?
- mixture spots dissolving in solvent
- some chemicals in mixture won't dissolve as much and stick to stationary phase quickly
- identify chemicals using positions on. chramtogram
**Rf values are fixed unless temp, solvent or make up of TLC plate changes**
104
How does Gas Chromatography work?
- used to separate a mixture of liquids that are volatile to be identified
1. when sample injected into machine and carried by inert gas (nitrogen), each substance will take different amount of time to travel through the column and reach detector
2. retention time= time it takes to reach detector (the difference between time at top of peak and 0)
3. each peak is a different substance so each has diff retention times which can be compared with known values in data tables
**area under peak tells us amount of each substance**
105
How would you find the concentration of substances using gas chromatography?
- use a calibration curve using known concentrations and the area under peaks of GC
- use serial dilutions and measure the area under the peak they form during GC
106
What is TMS?
- tetramethylsilane is a chemical used as a standard when looking at a chemical shift in NMR spectra
- as nuclei absorb different amounts of energy at different frequencies, measure magnitude with a standar TMS
- Chemical shift= difference between TMS peak and peaks produced by substance
- the chemical shift for TMS is therefore, 0
107
What solvents must be used in proton NMR?
- can't use H based solvents like water as they would show proton peaks
- use _deauterated_ substances like D2O which is an isotope of H
- only will show peaks from sample which is good
108
How can we identify OH or NH in proton NMR?
- it is difficult to identify specific OH and NH peaks as sit in broad area of spectrum
- use a method called proton exchange where we add D2O to a sample and run 2 spectra (one with and one without)
- if there is OH or NH proton in sample, deaterium will take its place
- **if OH/NH, it won't be found in spectra with D2O but will show peak on without**
