unit 2a: synthesis Flashcards
homolytic fission
involves the bond breaking evenly, meaning one electron from the shared pair in the bond goes into each atom, usually occurs in non-polar bonds
free radicals
the result of homolytic fission, highly reactive species with unpaired electrons
heterolytic fission
involves the bond breaking unevenly- with one atom getting both electrons from the bond and the other getting none, usually occurs in polar bonds
result of homolytic fission
free radicals
result of heterolytic fission
positive and negative ions
curly arrow notation
used to show the movement of electrons
a single headed arrow
represents the movement of a single electron
a double headed arrow
represents the movement of a pair of electrons
two categories of attacking groups
electrophiles and nucleophiles
electrophiles
atoms or groups of atoms which are deficient in electrons, usually have a positive or partial positive charge and are able to accept electrons, they are attracted to a region of negative charge or groups that can donate electrons
electrophile examples
Na^+, Mg^2+, NH4^+, NO2^+
carbocations
positive carbon based ions
nucleophiles
atoms or groups of atoms which are rich in electrons, usually have a negative or partial negative charge or lone pairs and are able to donate electrons, they are attracted to a region of positive charge or groups that can accept electrons
nucleophile examples
Cl^-, CN^-, H2O, C=C, OH^-, NH3
elimination reactions
when atoms are removed from a molecule and a double bond is formed, they are the opposite of addition reactions
substitution
when an atom or functional group is replaced by a different atom or functional group
three types of substitution
free radical, electrophilic, nucleophilic
free radical substitution
when UV light is used to trigger a free radical chain reaction
electrophilic substitution
when an electrophile attacks a compound
nucleophilic substitution
when a nucleophile attacks a compound
monohaloalkanes can be made by
reacting alkanes with a halogen (free radical substitution), reacting a hydrogen halide with an alkene (addition), synthesised from alcohols
addition
a reaction where a small molecule adds onto an unsaturated molecule by reacting with the C=C double bond
condensation
a reaction where two molecules combine to form a larger molecule, by eliminating a smaller molecule
hydrolysis
a reaction where a molecule is broken down, by reaction with water
oxidation
oxidation causes and increase in the oxygen to hydrogen ratio
reduction
reduction causes a decrease in the oxygen to hydrogen ratio
neutralisation
a reaction between an acid and a base, most examples involve carboxylic acids reacting with bases, e.g. alkaline hydrolysis of fats/oils using sodium hydroxide in the making of soaps
haloalkanes and nucleophilic substitution
the carbon - halogen bond is highly polar, the carbon is partially positive so it can be attacked by a nucleophile
the two nucleophilic substitution mechanisms
Sn1, Sn2
Sn2 is undergone by
primary and secondary haloalkanes
process of Sn2
the rate determining step (two molecules), transition state/activated complex, final molecule
Sn1 is undergone by
tertiary haloalkanes
process of Sn1
rate determining step (one molecule), final molecule
reasons for primary and secondary undergoing Sn2 and tertiary undergoing Sn1
steric hindrance, carbocation stability
steric hindrance
in primary and secondary haloalkanes there is space for the nucleophile to attack the carbon, in tertiary there is not
carbocation stability
tertiary carbocations are more stable due to inductive stability therefore can exist long enough to undergo Sn1
haloalkanes into alcohols
nucleophilic substitution using a base in water
haloalkanes into ethers
nucleophilic substitution using alkoxides
haloalkanes into nitriles into carboxylic acids
nucleophilic substitution using sodium cyanide in ethanol and react nitrile with aqueous acid
monohaloalkane and elimination
react monohaloalkane with a strong base (NaOH) in ethanol, the halogen atom and a hydrogen atom on adjacent carbons are removed and an alkene is formed
making alkenes
dehydration of alcohols (catalyst), base induced elimination of hydrogen halides from monohaloalkanes
markovnikovs rule
when an unsymmetrical molecule is added to an unsymmetrical alkene, the hydrogen atom becomes attached to the carbon with the most hydrogens already attached
why are two products make in alkene synthesis
stability of the carbon intermediate, secondary carbocation is much more stable so will occur more often
forming monohaloalkanes with hydrogen halides from alkenes
electrophilic addition with a hydrogen halide added to a double bond
forming alcohols with water from alkenes
adding water to alkenes uses water with electrophilic addition using an acid catalyst (HCl)
forming dihaloalkanes with halogens from alkenes
electrophilic addition when a halogen molecule is reacted with a double bond
forming alkanes with hydrogen from alkenes
electrophilic addition by adding hydrogen to an alkene, nickel catalyst is required
three ways of making alcohols
substitution of haloalkanes, acid catalysed hydration, reduction of carbonyl compounds
reduction of carbonyl compounds
alcohols are produced by this using a reducing agent e.g. LiAlH4
aldehydes are reduced to
primary alcohols
alcohols reaction with carboxylic acids
alcohols react to form esters, water is eliminated. conc. sulphuric acid is a catalyst
alcohols reaction with acid chlorides
esters are formed and a condensation reaction takes place
three ways of making carboxylic acids
oxidation of primary alcohols and aldehydes, hydrolysis of nitriles, hydrolysis of esters or amides
hydrolysis of esters and amides to carboxylic acids
carboxylic acids can be prepared by hydrolysis of esters, acid catalyst is required
four main carboxylic reactions
condensation with alcohols, reduction, reactions with metals/bases, reaction with ammonia/amines
carboxylic reactions with metals/bases
forms salts
carboxylic reactions with ammonia/ amines
forms amides when heated
five main reactions of alcohols
dehydration, reactive metals, oxidation, condensation with carboxylic acids, condensation with acid chlorides
ethers
organic compounds with general formula R-O-R’ where the Rs are alkyl groups
ethers uses
solvents as they are relatively inert
ethers properties
bp lower than their isomeric alcohol, soluble in water unless larger
amines
related to ammonia where one or more hydrogens are replaced by alkyl groups
amines properties
primary and secondary both contain the N-H bond so can form hydrogen bonding, lower bp for tertiary amines, soluble in water
amine reactions
mainly react with acids since they are bases to forms salts
aromatics structure
contain a benzene ring, when a hydrogen is replaced by another group this is called a phenyl group
aromatic reactions
benzene can undergo electrophilic substitution, the 4 types are: halogenation, nitration, sulfonation, alkylation
aromatic halogenation
react benzene with chlorine and a hydrogen is substituted with a chlorine atom
aromatic bromination
substituting hydrogen with bromine
aromatic nitration
benzene ring is attacked by the NO2+
aromatic sulfonation
substituting a hydrogen atom in the benzene ring for the sulfonic acid group (attacked by SO3) SO3H is added to benzene
aromatic alkylation
alkylbenzenes can be formed by reacting benzene with a haloalkane using an aluminium chloride catalyst
ketones are reduced to
secondary alcohols
electrophilic substitution involves
a benzene ring/ aromatic structure
alkoxides
powerful nucleophiles and bases e.g. C2H5O-Na+
making alkoxides
reacting an alkali metal e.g. Na with a dry sample of alcohol
reacting a monohaloalkane witn NaCN in ethanol…
produces a nitrile and increases the carbon chain by 1
nitriles can be converted to
carboxylic acids by acid hydrolysis using H+ ions as the catalyst (nucleophilic substitution reaction)
dehydration of alcohols catalyst
concentrated sulfuric acid (H2SO4)
base induced elimination
alkenes being produced from monohaloalkanes by heating with NaOH in ethanol
dehydration of alcohols produces
alkenes using conc H2SO4
oxidising agent
acidified dichromate
acid chloride
a carboxylic acid with the -OH replaced with chlorine
why is it more useful to react alcohols with acid chlorides than carboxylic acids
it is faster and does not require a catalyst
amides
molecules with a CONH2 group
phenyl group
when a hydrogen in a benzene ring is replaced by another group
catalyst for electrophilic substitution of a chlorine atom on benzene
AlCl3 (if with Br for example it would be AlBr3)
nitronium ion can be made by
mixing conc H2SO4 and conc HNO3
catalysts of alkylation of benzene
AlCl3
