3.2 - Synthesis Flashcards
explain basically bond fission
bonds in reactant molecules are broken and bonds in product molecules are made
what are the 2 types of bond fission
homolytic and heterolytic
what type of reaction does bond fission occur in?
organic
what does homolytic fission form
2 neutral radicals
what type of bond usually allows homolytic fission to occur?
a non-polar, sigma covalent bond
what happens in homolytic fission
each atom retains 1 electron when the bond is broken
why is homolytic fission unsuitable for organic synthesis
the reaction results in a very complex mixture of products
what does heterolytic fission form
2 oppositely charged ions
what type of bond allows heterolytic fission to occur
polar, sigma covalent bonds
what happens in heterolytic fission
1 atom retains both electrons when the bond is broken
what makes heterolytic fission suitable for organic synthesis
the reaction results in far fewer products than in homolytic fission
a single-headed arrow indicates
the movement of a single electron
a double-headed arrow indicates
the movement of an electron pair
the tail of the arrow shows
the source of the electron(s)
the head of the arrow indicates
the destination of the electron(s)
two single-headed arrows starting at the middle of a covalent bond indicate
homolytic bond fission is occurring
a double-headed arrow starting at the middle of a covalent bond indicates
heterolytic bond fission is occurring
an arrow drawn with the head pointing to the space between two atoms indicates
that a covalent bond will be formed between those two atoms
what are the 2 types of attacking group
nucleophiles and electrophiles
what are nucleophiles “rich” in
electrons
give examples of nucleophiles
Cl⁻ Br⁻ OH⁻ CN⁻ NH₃ H₂O
what are nucleophiles attracted to
atoms bearing a partial or full positive charge
what are nucleophiles capable of
donating an electron pair to form a new covalent bond
electrophiles are deficient in what
electrons
give examples of electrophiles
H⁺ NO₂⁺ SO₃
what are electrophiles attracted to
atoms bearing a partial or full negative charge
what are electrophiles capable of
accepting an electron pair to form a new covalent bond
what does e-anchors stand for
elimination addition neutralisation condensation hydrolysis oxidation reduction substitution
what is the maximum number of steps needed to devise a synthetic route for a given reactant to a final product
3
how is a haloalkane (alkyl halide) created
one or more hydrogen in an alkane is substituted for a halogen atom
what is a monohaloalkane
a haloalkane which contains 1 halogen atom
what do monohaloalkanes form in an elimination reaction
alkenes
what is used in the monohaloalkane elimination reaction
a strong base such as potassium or sodium hydroxide in ethanol
nucleophilic substitution of a monohaloalkane with aqueous alkalis forms what
alcohols
nucleophilic substitution of a monohaloalkane with aqueous alcoholic alkoxides forms what
ethers
nucleophilic substitution of a monohaloalkane with ethanolic cyanide forms what
nitriles (chain length increases by one) (these can be hydrolysed to carboxylic acids)
what are the 2 types of nucleophilic substitution mechanism
Sₙ1 and Sₙ2
explain Sₙ1 nucleophilic substitution
- has 1 species in its rate determining step
- occurs in a minimum of 2 steps via a trigonal planar carbocation intermediate
explain Sₙ2 nucleophilic substitution
- has 2 species in the rate determining step
- occurs in a single step via a single five-centred, trigonal bipyramidal transition state
how can alcohols be prepared
haloalkanes by substitution
alkenes by acid-catalysed hydration (addition)
aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride
how are alcohols dehydrated to alkenes
using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
how are alcohols oxidised to form aldehydes then carboxylic acids / ketones
using acidified permanganate, acidified
dichromate or hot copper(II) oxide
what does an alkoxide contain
O⁻
how are alcohols made into alkoxides
reaction with some reactive metals such as potassium or sodium
what catalysts can be used in the formation of ethers from alcohols and carboxylic acids
concentrated sulfuric acid or concentrated phosphoric acid
what is the functional group in an acid chloride
COCl (C=O / C-Cl)
what catalysts need to be used in the formation of esters from alcohols and acid chlorides?
no catalysts are needed
which is a faster reaction, ester formation from alcohol and carboxylic acid, or alcohol and acid chloride
alcohol and acid chloride
how is an alkyl group formed from an alkane
one hydrogen is removed
what is the general structure for substituted alkane ethers
R’ - O - R” where R’ and R’’ are alkyl groups
what can ethers be regarded as
substituted alkanes
how is an ether formed
a hydrogen is removed from an alkane, and is replaced with an alkoxy group
describe a process in which an ether is produced
the nucleophilic substitution reaction between a monohaloalkane and an alkoxide
which ethers are soluble in water
methoxymethane and methoxyethane
what type of ethers are insoluble in water and why
large ethers, as they have a large molecular size
why are ethers commonly used as solvents
they are relatively inert chemically and will dissolve many organic compounds
how can alkenes be prepared
- dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
- base-induced elimination of hydrogen halides from monohaloalkanes
what electrophilic addition reactions can alkenes take part in
- with hydrogen to form alkanes in the presence of a catalyst
- with halogens to form dihaloalkanes
- with hydrogen halides to form monohaloalkanes
- with water using an acid catalyst to form alcohols
what does Markovnikov’s rule state
that when a hydrogen halide or water is added to an unsymmetrical alkene, the hydrogen atom becomes attached to the carbon with the most hydrogen atoms already attached to it.
which product formed follows Markovnikovs rule
the major product
how can carboxylic acids be produced
- oxidising primary alcohols using acidified permanganate, acidified dichromate and hot copper (ii) oxide
- oxidising aldehydes using acidified permanganate, acidified dichromate, Fehling’s solution and Tollens’ reagent
- hydrolysing nitriles, esters or amides
reactions of carboxylic acids include:
- formation of salts by reactions with metals or bases
- condensation reactions with alcohols to form esters in the presence of concentrated sulfuric/phosphoric acid
- reaction with amines to form alkylammonium salts that form amides when heated
- reduction with lithium aluminium hydride to form primary alcohols
how are amines formed
1 or more hydrogen atoms from ammonia are replaced by an alkyl group
are amines acidic or basic
basic
which amines display hydrogen bonding
primary and secondary
are amines strong or weak bases
weak
how do amines produce hydroxide ions with water
the nitrogen atom has a lone pair of electrons which can accept a proton from water
what is the chemical formula for benzene
C6H6
what is the simplest member of the class of aromatic hydrocarbons
benzene
why is benzene stable
the delocalisation of electrons in the conjugated system
why does benzene not take part in addition reactions
delocalised electrons are present
how is a phenyl group formed
one hydrogen atom is substituted for another group in a benzene molecule
what is the formula for a phenyl group
-C6H5
Benzene rings can take part in electrophilic substitution reactions. Reactions at benzene rings include:
halogenation by reaction of a halogen using aluminium chloride or iron(III) chloride for chlorination and aluminium bromide or iron(III) bromide for bromination
alkylation by reaction of a haloalkane using aluminium chloride
nitration using concentrated sulfuric acid and concentrated nitric acid
sulfonation using concentrated sulfuric acid
