6.1 Flashcards
what state is benzene at rtp
liquid
what kind of hydrocarbons contain a benzene ring
aromatic
whats benzenes reactivity
very stable and resistant to substitution and addition
limitations of kekules model of benzene
benzene is a perfect hexagon, kekules model had double and single bonds, which are different lengths (double shorter)
less reactive than expected with the double bonds in kekules model (eg electrophilic sub needs a catalyst)
hydrogenation is much less exothermic than expected
who created a model of benzene taht was wrong
kekule
what is benzenes actual structure called
delocalised electron structure
how is benzene bonded
p orbitals overlap to form pi bonds in a ring of delocalised pi electrons above and below the plane of the molecule
how is benzene drawn skeletally
hexagon with a circle in it
what is an arene
aromatic compounds that contain a benzene ring as part of their structure
what is benzene molecular formula
C6H6
which electrons are delocalised in benzene
the outer electron form the p orbital of each carbon atom
what feature of benzene makes it stable
delocalised ring structure
what was kekules model of benzene
cyclohexane with three double bonds
why doesn’t benzene undergo electrophillic addition
because that would break up the stable delocalised ring of electrons
why is benzene susceptible to attack from electrophiles
the ring is an area of high electron density
explain electrophillic substitution
electrophile attacks, arrow from ring to electrophile
unstable intermediate is formed, draw H and electrophile both attacked to one of the carbons and a disrupted ring with a plus in the middle, with the opening facing the carbon with the electrophile and an arrow from the C-H bond to the ring through the gap
then draw benzene with the electrophile attached and draw H+ off on its own
what does localised mean
an electron/pair that is associated with a specific atom/s
what is delocalised
electrons that are not associated with specific a atom/s
what is planar structure
a molecule where all of its atoms lie in the same plane
what’s the use of a catalyst in the halogenation of benzene
it generates the electrophile
what type of catalyst do you need in halogenation of benzene
a halogen carrier
give examples of halogen carriers and the equations for the electrophile being generated and catalyst regeneration
AlCl3 or FeCl3
eg:
Cl2 + FeCl3 —> FeCl4^- + Cl^+
FeCl4^- + H^+ —> FeCl3 + HCl
what is the electrophile in the halogenation of benzene
the halogen +
eg Cl^+
what are the reagents in the halogenation of benzene
halogen and halogen carrier
what are the reagents in the halogenation of benzene
halogen and halogen carrier
what are the conditions for the halogenation of benzene
reflux
what is the electrophile for the nitration of benzene
NO^2+
what are the reagents in the nitration of benzene
conc nitric acid and conc sulphuric acid
what is the catalyst in the nitration of benzene
conc sulphuric acid
what are the equations showing the nitration of benzene including the regeneration of the catalyst
HNO3 + H2SO4 —> NO2^+ + HSO4^- +H2O
C6H6 + NO2^+ —> C6H5NO2 + H^+
HSO4^- + H^+ —> H2SO4
what are the conditions of the nitration of benzene and why
reflux at 55°C (to prevent further substitution of another NO2)
what are the reagents for friedel-crafts alkylation
haloalkane and anhydrous aluminium chloride (AlCl3)
what are the conditions for the alkylation of benzene
room temperature
what is the electrophile in the alkylation of benzene
a carbocation alkyl group eg: CH3+ or C2H5+
what are the reactions for the formation and regeneration for the catalyst in alkylation of benzene
CH3Cl + AlCl3 —> AlCl4^- + CH3^+
AlCl4^- + H+ —> AlCl3 + HCl
why is alkylation so important
increases the number of carbon atoms in a compound by forming carbon-carbon bonds
what are the reagents for acylation of benzene
an acyl chloride (R-COCl) and anhydrous aluminium chloride (AlCl3)
what’s re the conditions for acylation of benzene
reflux at 50°C
what are the conditions for acylation of benzene
reflux at 50°C
what’s the electrophile in the acylation of benzene
RC+O (eg: CH3C^+O)
so basically the acyl chloride with the chlorine removed
what are the equations for the use and regeneration for the catalyst in acylation of benzene
CH3COCl + AlCl3 —> AlCl4^- + CH3CO^+
AlCl4^- + H^+ —> AlCl3 + HCl
what is made form the acylation of benzene
a phenylketone
what happens when you put benzene in bromine water
nothing because the delocalised model of benzene makes it stable and not reactive enough to decolourise bromine water
what type of acids are phenols
weak but stronger than aliphatic alcohols because the O is more attracted to the benzene so it’s easier to lose the H+
why is phenol more reactive than benzene
the lone pair of electrons on the oxygen are delocalised into the benzene ring structure (electron donating group) which increases the electron density of the ring so less stable and more susceptible to electrophile attack and attack from weaker electrophile (can also induce dipoles in non polar molecules)
what do you need for the nitration of phenol
dilute nitric acid and no catalyst
what affect does the NO2 group have on electrons
electron withdrawing group
how does phenol react with NaOH
forms a soluble salt and water
how does phenol react with sodium
forms an ionic salt and hydrogen gas
what’s the difference between an aromatic alcohol and phenol
in phenol the OH group is attacked directly to the benzene ring nog an alkyl group attacked to the benzene
how does the oxygen in phenol react with the benzene ring
the p orbital on the O overlaps with the p orbitals in the ring
wh
where are reactions most likely to take place if there’s an electron donating group
2,4,6 because they are the most electron dense positions
which groups are electron donating
NH2 CH3 (alkyls) OH
what’s the effect of an electron withdrawing group
reduce the electron density of the aromatic ring and therefore reduces reactivity
what positions are most likely to react when there’s an electron withdrawing group
3,5
examples of electron withdrawing groups
NO2 CN CHO COOH
why are carbonyls soluble in water
they can form hydrogen bonds with water
why can’t carbonyls hydrogen bond to each other
they don’t have a delta positive hydrogen (bonded to F O N)
what are aldehydes
they have a carbonyl group on a carbon atom at the end of the carbon chain ( only attached to one other carbon)
what are ketones
have a carbonyl group on a carbon atom that is attached to two other carbon atoms
how to show oxidating and reducing agents in a reaction
[O] and [H]
how to make aldehydes
distil a primary alcohol
how to make ketones
reflux secondary alcohols
what is the colour change of potassium dichromate when an alcohol is oxided
orange to green
how do you turn a carbonyl back into an alcohol
reduce it via nucleophilic addition with NaBH4
where do nucleophiles attack carbonyls
the delta positive carbon centre
how does a nucleophilic reaction get drawn
arrow from nucleophiles lone pair or negative charge to the delta positive carbon, arrow from the double bond to the delta negative oxygen
attach nucleophile where it attacked, oxygen now has three lone pairs and is negative, arrow from one lone pair to and H+
new product formed with nucleophile on one bit and OH where the O was
what are the reagents for the addition of HCN to a carbonyl
refluxed with KCN and NaCN both need to be acidified to get the H+ needed
why do you use acidified KCN instead of just HCN when adding HCN
because HCN is very toxic and is a weak acid that struggles dissociating into its ions (KCN is ionic so produces more of CN- nucleophile)
what is the nucleophile in the nucleophilic addition of HCN to a carbonyl
CN- (has a triple bond)
what does the addition of HCN to a carbonyl make
hydroxynitriles
what’s the difference of the CN- attacking the carbonyl from above or below the planar double bond C=O
creates two different optical isomers becuase they are chiral carbons so they are different enantiomers
what is the nucleophile when reacting a carbonyl with NaBH4
H:-
how can you test for carbonyls
add 2,4-DNPH
a yellow orange or reddish orange precipitate will form if it is a carbonyl
why is the melting point of carbonyls useful
becuase they have sharp melting points so the melt over a narrow range of temperatures so you can determine what they are
how do you recrystallise
dissolve in minimum amount of hot water
cool to allow crystals to form and filter under reduced pressure
leave to dry
how do you recrystallise
dissolve in minimum amount of hot water
cool to allow crystals to form and filter under reduced pressure
leave to dry
what test can identify aldehydes from ketones and how
tollens reagent (a layer of silver will form on the walls of the test tube) it will remain colourless if it’s a ketone
it works because it oxidises the aldehyde to a carboxylic acid and reduces silver ions to silver
what are optical isomers
molecules that are non-superimposable mirror images of each other. they have the same chemical properties but interact with polarised light differently
what are the conditions needed for the addition of NaBH4 to a carbonyl
aqueous or alcoholic solution
how many reducing agents are needed in the addition of NaBH4 to a carbonyl
2
what happens to aldehydes and ketones in the addition of NaBH4 to a carbonyl
aldehydes reduced to primary alcohols
ketones reduced to secondary alcohols
what happens to boiling point of carboxylic acids as chain length increases
increases as more london forces
how is boiling point affected for straight chain isomers of carboxylic acids
it increases because there’s more surface contact
why are carboxylic acids soluble
because they can hydrogen bond
whats it called when carboxylic acids hydrogen bond with eachother twice
dimerisation
what happens to solubility as chain length increases
it decreases as the longer chain obscures the functional group whcih is the big that can dissolve
name and explain two derivatives of carboxylic acids (COOH)
acyl chlorides (COCl) the OH group is &replaced by a chlorine
acid anhydrides (two carboxylic acids joined together by their OH groups just with one O, so one H2O is removed)
carboxylic acids are strong enough acids to…
literature CO2 from carbonates (fizz)
reagent of chlorination of carboxylic acids
thionyl chloride (SOCl2) and dry conditions
what does the chlorination of a carboxylic acids make
an acyl chloride, SO2 (or other reagent leftovers) and HCl
how do you name acyl chlorides
take of the -ic from the carboxylic acid and replace with -yl chloride
eg ethanoyl chloride from ethanoic acid
what reactions do acyl chlorides undergo
nucleophilic addition-elimination reactions (basically nucleophilic substitution)
what does acyl chloride and water make
carboxylic acid
what does acyl chloride and alcohols make
esters
what does acyl chloride and ammonia make
amide
what does acyl chloride and amines make
N-substituted amide
how are esters named
alcohol-yl carboxylic acid-anoate
what are the reagents and conditions of esterification
carboxylic acids and alcohols refluxed with strong acid catalyst (usually conc sulphuric acid)
what does esterification make and where does it come from
makes H2O, one H from the alcohol, the OH from the carboxylic acid
why would you use an acid anhydride in esterification over an acyl chloride and what reaction are both of these
addition elimination mechanism
becuase it doesn’t produce toxic HCl as a side product
but the reaction is slower
what are the conditions for esterification using an acyl chloride
and what’s it’s by product
reflux under dry conditions
HCl gas
what are the conditions for esterification using an acid anhydride
and what’s it’s by product
reflux under dry conditions
a carboxylic acid
how does the hydrolysis of esters link with esterification
it’s the opposite reaction (splitting up an ester by adding water)
what happens if an ester and water react with hot aqueous acids
makes parent alcohol and carboxylic acid
what happens if an ester and water react with hot aqueous alkali
what’s the process called
makes a carboxylate salt (with the metal of the base often Na) and an alcohol (doesn’t react with the base becuase alcohols are weak acids and only react with concentrated bases)
process is called saponification
why do acyl chlorides react so violently
due to the very polar COCl group
how do you name benzene if it has a group attached that is more reactive
use it as the prefix phenyl
what groups are more reactive than benzene and why
OH (lone pairs)
NH2 (lone pairs)
CH=CH2 (alkenes because of the double bond)
