Theory Flashcards
Why chain isomers have different physical properties
Shape of molecule has changed
Do positional isomers have different chemical and physical properties
Yes
Do fg isomers have different chemical and physical properties
Yes
What shape is alkane molecules and why
Tetrahedral (109.5)
4 bonded pairs
All repel equally
What force is between alkane molecules
Induced dipole dipole
Why does propane have a high boiling point than methane
Propane is longer
So has stronger induced dipole dipole forces
Because it has more surface contact and more electrons to interact
So takes more energy to overcome
Why does a branched chain have a lower bp than a straight alkane
Branched chains can’t pack as closely together
And have smaller molecular surface areas
So weaker induced dipole dipole forces
So less Energy needed to overcome
Why do liquid alkanes need to be vaporised before combustion
Only happens in gaseous states
What type of alkanes are more volatile
Small
Why are long alkanes good fuels
Have lots of bonds to break
So release lots of energy per mole
Why is CO toxic
Oxygen is carried by haemoglobin
CO is better at binding to haemoglobin than oxygen
So no oxygen is carried around the body
Leads to oxygen deprivation
What reaction type is used in free radicals
Free radical substitution
Write the reaction mechanism for free radical substitution
Cl2 -> 2Cl🖤
Cl🖤 + CH4-> CH3🖤 + HCl
CH3🖤 + Cl2 -> CH3Cl + Cl🖤
Cl🖤 + CH3🖤 -> CH3Cl
What is the 2 problems with free radical substitution
You get a mixture of products that need to be filtered
And the substitutions can happen anywhere along the alkane chain
How to stop a mixture of products in free radical substitution
Having excess alkane
So the free radical is more likely to react with that Than a chloromethane molecule
Why are alkenes more reactive that alkanes
Alkenes contain a pi and sigma bond
The double bond contains 4 electrons = high electron density
Pi bond sticks out from the rest of the molecule
Attracts electrophiles
Pi bond has low bond enthalpy so doesn’t take much energy to overcome
Why are alkanes unreactive
Only contain sigma bonds
High bond enthalpy = take a lot of energy to overcome
Non polar = dont attract electrophiles or nucleophiles
Why can’t double bonds rotate
Because of how the p orbitals overlap
What is the shape around Alkenes
Tribunal planar
Why can alkenes form stereoisomers
Due to lack of rotation from double bonds
What happens about naming stereoisomers when all the groups are different
Assign each group a priority on each C atom
What are e isomers also called
Trans
What are z isomers also called
Cis
When does the cis/trans naming system not work
When all groups are different
What type of reaction do alkenes undergo
Electrophilic addition
How do you know what product will be the most stable in a unsymmetrical alkane when a hydrogen halide is being added
Carbon with the most alkyl groups is the most stable
Feeds the most electrons into the carbon atom
Forms a more stable carbocations
Why are small alcohols soluble in water
H bonds form between water and the OH group
Most of the chain is polar so it fully dissolves
Why are long alcohols not as soluble
Most of the chain isn’t polar so can’t h bond with the water
Why do alcohols have a low volatility
They can h bond between molecules
Takes lots of energy to overcome
Why do aldehydes have to be distilled off as soon as it’s formed
The aldehyde boils at a lower temp that the alcohol
So need to be distilled off fast before it oxidises too far into a carboxylic acid
What is the only way of oxidising a tertiary alcohol
Burning
What type of reaction is it when haloalkanes react with alkali
Nucleophilic substitution
Why do iodo alkanes get hydrolysed the fastest
They have the weakest bond (lowest bond enthalpy) so requires less energy to overcome
What are cfcs
Only contain carbon fluorine and chlorine
All h atoms have been replaced by halogens
How is ozone formed
O2 -> O+O (UV)
O2 + O -> O3
Why are cfcs bad
Catalyse break down of ozone
Causing holes in ozone in atm
Let in harmful Uv
Write the mechanism of cfcs destroying the ozone
CF2Cl2 -> 🖤CF2Cl + Cl🖤
Cl🖤 + O3 -> O2 + ClO🖤
ClO🖤 + O -> O2 + Cl🖤
Overall = O3 + O -> 2O2
Why are Cl🖤 so bad
They are regenerated
So are a catalyst
So 1 Cl🖤 destroys lots of ozone before it forms a stable compound
What other compound besides Cl🖤 destroys the ozone
NO🖤
Why is the kekule model incorrect
X ray diffraction = all carbon to carbon bonds are the same length, between the lengths of a single and double bond
Enthalpy change of hydration = much less exothermic than expected at 208 instead of 360. Meaning the bonds are stronger than expected = more stable
Doesn’t readily undergo electrophilic addition = bromination needs heat and UV light but cyclohexene does it at room temp.
What reaction does benzene undergo
Electrophilic substitution;
Why is a halogen carrier needed for reactions with benzene
The electrophile has to be strong to attack a benzene ring because it’s so stable
The halogen carrier accepts a lone pair of electrons from the halogen atom of an electrophile . Polarising the electrophile making it more strongly attracted to the benzene ring
Draw the mechanisms for benzene + Br2
-
What reactants are needed for a friedel craft alkylation
Haloalkane
AlCl3
Benzene
What reactants are needed for a friedel craft acylation
Acyl chloride
Alcl3
Benzene
What is the catalyst used in the format of nitrobenzene
Conc H2SO4
What is the equation of the formation of the nitronium ion
Hno3 + H2SO4-> h2no3+ + hso4-
H2no3 -> no2+ + h2o
Why does the temp need to be kept below 55 for the nitration on benzene
To stop multiple substitutions which make a explosive substance
Draw the nitratation of benzene mechanism
-
Why is phenol more reactive than benzene
Contain OH group
The O atom in a p orbital has electrons that overlap the delocalised electron ring
The lone pair becomes partially delocalised into the pi system
Increasing the electron density of the ring
More likely to be attack by electrophiles
Why are some groups donating
They have electrons in orbitals which overlap into the tepee delocalised electron ring
Increasing electron density at 2,4,6
Electrophiles more attracted to these positions
What are the electron donating groups
Nh2
oh
EDG
Why are some groups withdrawing
Doesn’t have any electrons in orbitals that overlap with the delocalised electron ring
Also electro negative
So reduce electron density from the ring
At 2,4,6
Most electron dense at 3,5
So electrophiles more attracted there
What is the product of bromine + phenol
2,4,6 tribromophenol
How do you know phenol has reacted with bromine
Forms precipitate in water
Decolourises
What is the ph of phenol
3/4
Weak acid
Why does phenol not react with sodium carbonate
Phenol isn’t a strong enough acid
What is used to reduce aldehydes and ketones back to alcohols
NaBH4
Dissolved in water and methanol
What supplies the nucleophile in the reduction of ketones and aldehydes
H- from NaBH4
It has a lone pair of electrons
What compound does HCN make with carbonyl compounds
Hydroxynitriles
What type of solution is HCN
Weak acid
What is the electrophile in the formation of hydroxynitrileS
CN-
What type of reaction is the reduction of ketones/aaldehydes
Nucleophyllic addition
What type of reaction is the formation of hydroxynitriles
Nucleophilic addition
What precautions are used in the lab when making a hydroxynitriles
Used acidified sodium cyanide instead of HCN because HCN is highly toxic
Done in fume cupboards
Why are carboxylic acids soluble in water
Can h bond due to polar oh and o group
What is the fg of acyl chlorides
COCl
How are acyl chlorides made
Carboxylic acid + SOCl2
What happens when acyl chloride + water
Carboxylic acid + HCl
Vigorous
Cold
What happens when acyl chloride + alcohol
Ester + HCl
Vigorous
Room temp
What happens when acyl chloride + ammonia
Primary amide
+ HCl
Violent
Room temp
What happens when acyl chloride + amines
Secondary amide + HCl
Violent
Room temp
What products would u actually get in a lab when ammonia + ethanoyl chloride
Ethanamide
HCl
Ammonium chloride
Because the HCl product reacts with the ammonia reactant
Which is the most effectuent way of making an ester
Alcohol + acyl chloride
Faster
And irreversible
What reaction type do acyl chlorides undergo
Nucleophilic addition elimination
What is the reaction between ethanoyl chloride + phenol
Phenyl ethanoate + HCl
Describe the formation of an ester from alcohol + carboxylic acid
Conc H2SO4 catalyst
Reversible = need to separate product as it’s made by distillation or reflux
Water produced
Describe estérification from alcohol and acid anhydride
No catalyst
Separate by fractional distillation
Ester + carboxylic acid produced
Describe base hydrolysis
Splits ester into carboxylic acid and aldohol
Reflux
Dilute acid
Reversible reaction
How do u keep the postsotion of eqm to the right in acid hydrolysis
Add lots of water
Explain base hydrolysis
Reflux
Dilute alkali (naoh)
Forms carboxylate salt and alcohol
What is an amine
H replaced in NH3 by an organic group
What type of solution are amines
Basic
What are amines bases
There is a lone pair on NH3
So it can accept a proton
What is the reaction with ethylamine + HCl
Ethylammonium chloride
Ch3Ch2NH3+Cl-
How do you make amines
Haloalkane + ethanolic ammonia
How do you separate primary secondary and tertiary amines
Fractional distillation
Why do you get a mixture of primary secondary and tertiary amines
More than one H is likely to be substituted on NH3
What is the reaction of ammonia + bromoethane
Ethylamine + NH4Br
How do you form diethylamine
Nh3 + ethylamine + bromoethane
How do you make aromatic amines
Reduce nitrobenzene
Nitrobenzene + tin metal + conc HCl
Reflux
Add NaOH
Makes phenyl amine + 2H2O
What are amides
Have the functional group conh2
Why do amides behave differently to amines
The carbonyl group on CONH2 pull electrons away from the Nh2
What is a secondary amide
One of the H is replaced by a methyl group
Amino acid + alkali
Forms salt + water
Amino acid + acid
Salt
Amino acid + alcohol
Ester + H2O
H2SO4 catalyst
What is a chiral center
Carbon atom with 4 different groups attached
What are optical isomers
Mirror images of each other
Can’t be super imposed
Optically active
What does optically active mean
They rotate the plane polarised light
What are polymers
Long chains of monomers joined together
Wh at are addition polymers
Double bond opens up
What is condensation polymerisation
Formed from 2 types of monomers
Functional groups link
Small molecules lost (H2O)
How are polymers broken down
Hydrolysis
Water added back
Done with acid abs base
What is acid hydrolysis
Add H+
Forms dicarboxylic acid and diamine
What is base hydrolysis
Dicarbocylate acid salt
Diol
What is a CN-
A nucleophile
What will CN- react with
React with carbon centres With a partially positive charge
Forming a new c -c bond
Forms a nitrile
How to increase length of carbon chain by addicting cyanide
Add HCN to slightly positive carbon
What type of reaction is haloalkanes + cyanide
Nucleophilic subsituation
How to form nitrile but from haloalkane
Reflux haloalkane with KCN in ethanol
Using nuclephylic substitution
How do you form a hydroxynitriles
Aldehyde/ketone + HCN
Why are nitrile groups useful in synthesis
Very reactive so can be replaced by other fg
How to reduce a nitrile to a primary amine
LiAlH4
+ Dilute acid
Or
Sodium metal + ethanol
What method is used to reduce nitriles in industry
Adding h gas and metal catalyst (Ni) at high Temp and pressure by catalytic hydrogenation
Why is catalytic hydrogenation used in industry
LiAlH4 and sodium is too expensive
How is a nitrile reduced to a carboxylic acid
Reflux with a dilute HCl
