Synthesis - organic Flashcards
Bond fission
Where bonds are broken in a chemical reaction
Homolytic fission definition
When a covalent bond breaks and each atom gets one electron from the former bond meaning free radicals are formed.
Types of bond fission
Homolytic + heterolytic
Why are free radicals unsuitable for synthesis
Because free radical reactions form complex mixtures of products.
Free radical reaction stages
Initiation
Propagation
Termination
Initiation
A stable molecule breaks down into two free radicals under UV.
Propagation
Where a free radical bonds with a stable and forms a free radical and a stable. Then this happens again forming the original free radical.
Termination
Where two free radicals bond forming a stable molecule.
Arrows in free radical reactions
Initiation: arrow goes away from both stable atoms.
Propagation: free radical towards stable, stable towards free radical, stable away from free radical.
Termination: free radicals towards each other.
Heterolytic fission
Where a covalent bond breaks and one atom retains both electrons from the covalent bond, meaning oppositely charged ions are formed.
When does heterolytic fission occur
When the bond between atoms is a polar covalent bond.
Why is heterolytic fission suitable for synthesis
Heterolytic fission results in fewer products.
Homolytic versus heterolytic fission
Homolytic forms free radicals
Heterolytic forms ions
Homolytic is suitable for synthesis
Heterolytic is unsuitable for synthesis
Homolytic occurs with non polar bonds
Heterolytic occurs when bonds are polar.
Haloalkanes types
Primary , secondary and tertiary
Haloalkanes
A halogen bonded to an alkane at a hydrogen.
What type of reaction is undergone by monohaloalkanes
Nucleophilic substitutions
Nucleophile definition
A chemical species which is an electron rich, negatively charged ion containing a non bonding electron pairs that it donates to form dative bonds.
Electrophile
A chemical species which is electron deficient and a positively charged ion which receives non bonding electron pairs from a nuleophile forming a dative bond.
Carbon halogen bond properties in haloalkanes
Carbon halogen bonds are polar and the carbon is delta positive and halogen is delta negative, this makes the carbon susceptible to nucleophilic attack.
Nucleophilic attack
Where a nuleophile bonds with a delta positive atom involved in a polar covalent bond by pushing out the delta negative atom.
Formation of alcohol from haloalkane
KOH + haloalkanes —> alcohol + KCl
Formation of ether from haloalkane
CH3O- + haloalkane —> ether + ionic substance
Ether
A molecule with C-O-C
Formation of carboxylic acid from haloalkane
Haloalkane + CN- ——> nitrile alkane
Nitrile alkane + H2O/H+—-> carboxylic acid
Acid hydrolysis
Where H2O/H+ is added to an alkane nitrile and forms a carboxylic acid
Types of reaction mechanism
SN1
SN2
SN1 stands for
First order nucleophilic substitution
SN2 stands for
Second order nucleophilic substitution
When does SN1 occur
When the haloalkane is tertiary
When does SN2 occur
When the haloalkane is primary
SN1 step 1
Tertiary haloalkane —> carbocation +halogen ion.
Heterolytic fission
SN1 step 2
Carbocation + OH- —-> tertiary alcohol
SN2 step 1
Primary haloalkane —> negative ion intermediate —-> primary alcohol
Features of SN1
The tertiary haloalkane will have more steric hinderance which means there isn’t enough space for the attacking nucleophile.
Features of SN2
The primary carbocation is less stable than the tertiary carbocation and therefore more unlikely to form.
Carbocation
A carbon molecule with a positive charge which a nuleophile will bind with
Steric hindrance
Where there is a large bulk of non polar atoms on the molecule.
Reagent of alcohol formation in nucleophilic substitution
KOH
Solvent of alcohol formation in nucleophilic substitution
Water (H2O)
Reagent for ether formation in nucleophilic substitution
KCH3O
K+(CH3O)-
Solvent for ether formation
ethanol
Process for producing carboxylic acid from haloalkane
Haloalkane reacts with cyanide ions (solvent ethanol) to form nitrile.
Nitrile reacts with H+/H2O to form carboxylic acid.
Nucleophile charge
Negative (similar to ligands)
Electrophile charge
Positive
Arrows on SN1
In stage 1 double head arrow to halogen
In stage 2 double head arrow towards carbocation
Arrow heads for SN2
Double head arrow to carbon in centre.
SN1 mechanism kinetics
1st order overall nucleophilic substitution
SN2 mechanism kinetics
2nd order overall nucleophilic substitution
Alcohols melting and boiling points
Higher than other homologous series due to hydrogen bonding in the hydroxyl group.
Alcohols solubility rule
Short chain alcohols are soluble in water, as the chain length increases the solubility decreases due to non polar bonds.
Methods of alcohol preparation
Acid hydration of Alkenes
Reduction of aldehydes and ketones using lithium aluminium hydride
Nucleophilic substitution of haloalkanes.
Lithium aluminium hydride
Li+[AlH4]-
Alcohol condensation
Alcohol + carboxylic acid - -> ester + water
Ester naming rule
Alcohol becomes branch, carboxylic acid or acid chloride becomes branch.
Condensation of alcohol by more effective method
Alcohol + acid chloride —> ester + HCl
Acid chloride
A carboxylic acid with Cl instead of OH
Alcohols primary oxidation
Aldehyde then carboxylic acid
Alcohols secondary oxidation
Ketone
Alcohols dehydration
Alcohol —->Alkene
Concentrated sulphuric acid or phosphoric acid catalyst.
Lithium aluminium hydride
Alcohol reaction with alkali metals
Alcohol + alkali metal —.> metal alkoxide + Hydrogen
Ch3OH + Na - > CH3ONa + H2
Ether naming formula
Alkoxy - main chain.
Ethers physical properties
Lack of hydrogen bonding will decrease mp + bp and decrease solubility in water.
Elimination reaction
A reaction where a small molecule is removed from another molecule.
Elimination reaction reagent (alcohol)
KOH
Elimination reaction solvent
Ethanol
Alkenes mechanism
Electrophilic addition
Markovnikov’s rule
During addition of an alkene the hydrogen will bind to the carbon with more hydrogens bonded.
Hydrohalogenation process
Double arrow from alkene double bond to delta positive hydrogen
Double arrow from bond to delta negative halogen.
Bromine nucleophile arrow to positive carbocation.
Acid catalysed hydration process
Double arrow from double bond on alkene to H+
Carbocation intermediate formed with markovnikovs rule.
Water arrow to positive carbocation to form positive oxygen ion
Hydrogen oxygen bond arrow to oxygen.
Halogenation mechanism
Di-halogen molecule will become temporarily delta positive and negative
Arrow goes from double bond to delta positive halogen
Arrow from halogen bond to delta negative bond.
Forms a triangle structure with bromine and bromine nucleophile.
Arrow to positive bromine ion
Arrow from bromine nucleophile to carbon.
Oxidation of aldehydes
Carboxylic acid
Oxidation of ketones
None
Oxidising agents for carbonyl compounds
Fehlings solution
acidified dichromate ions
Tollens reagent
Reducing agent for carbonyl compounds
Lithium aluminium hydride
Preparation of carboxylic acids
Primary alcohols and aldehydes oxidation
Hydrolysis of esters
Acid hydrolysis of nitriles
Carboxylic acid reaction with metal and base
Carboxylic acid + base - - salt + water
Carboxylic acid + metal makes salt + hydrogen
Amines
Molecules with NH2 functional group
Primary secondary and tertiary amine
The nitrogen is bonded to 1 2 or 3 carbons
Amines physical properties
Higher mp and bp due to hydrogen binding in primary and secondary amines
The solubility of amines that are primary and secondary in water is also higher.
PH of amines explanation
The line pair on the nitrogen allows for dative covalent binds to be formed with H+ ions, which shifts the water equilibrium to produce OH- ions
Amines reaction with inorganic acid
Acid + amine —-> ionic compound
CH3NH2 + HCl —> CH3NH3+CL-
Amines reaction to form amides
Amine + carboxylic acid —> ammonium salt + carboxylic ion —-> amides
Benzene structural formula
C6H6
Alternating single and double carbon bonds
Benzene bonding and reactions explanation
Benzene has sp2 hybridisation which allows for delocalised π electrons. This means it resists electrophiclic addition.
Benzene does undergo electrophilic substitution by replacing hydrogen with other molecules due to the polarity of the bond.
Electrophilic substitution process
Cl2 + AlCl3 —-> Cl+ + [AlCl4]-
Cl+ + benzene —-Chlorobenzene
Alkylation process
RCl + AlCl3 —-> R+ + [AlCl4]-
R+ + benzene —-> R benzene
Nitration
Electrophilic substitution of benzene when a nitronium ion is used
nitric and sulphuric acid are used
HNO3 + 2H2SO4 - -> 2HSO4- + H3O+NO2+
Sulphonation
Electrophilic substitution of benzene when a sulphonium ion is used.
Conc sulphuric acid is used
H2SO4 + H2SO4 —> H2O + HSO4- HOSO2+
Sulphonium ions + benzene —-> sulphonium benzene
