3.2 synthesis Flashcards
what happens to the bonds in the reactant molecules when an organic reaction takes place
they are broken and bonds in the product molecules are made
what is bond fission
the process of bond breaking
what are the two types of bond fission
homolytic and heterolytic
what is homolytic fission
this is when the electrons are separated equally, forming two neutral radicals
what occurs during homolytic fission
each atom retains one electron from the sigma covalent bond and the bond breaks evenly
when does homolytic fission usually occurs
when non polar covalent bonds are broken
what do reactions involving homolytic fission tend to result in the formation of
a very complex mixture of products, making them unsuitable for organic synthesis
what does heterolytic fission form
two oppositely charged ions
when does heterolytic fission form
when one atom retains both electrons from the sigma covalent bond and the bond breaks unevenly
when does heterolytic fission occur in relation to bonds
when polar covalent bonds are broken
what can be used to represent the movement of electrons during bond fission and bond making
curly arrow notation
what are attacking groups classified as in reactions involving heterolytic bond fission
nucleophiles or electrophiles
what are nucleophiles
negatively charged ions or neutral molecules that are electron rich, and they are attracted toward atoms bearing a partial or full positive charge. they are capable of donating an electron pair to form a new covalent bond
what are electrophiles
these are positively charged ions or neutral molecules that are electron deficient, and they are attracted toward atoms bearing a partial or full negative charge. they are capable of accepting an electron pair to form a new covalent bond
which reaction types can be identified from a chemical equation
substitution
addition
elimination
condensation
hydrolysis
oxidation
reduction
neutralisation
how can synthetic routes be devised
from a given reactant to final product
what can be deduced by looking at the structural formula
the possible reactions of a particular molecule
what is skeletal structural formula
neither the carbon atoms or any hydrogen attached to the carbon atoms are shown
the presence of a carbon atom is implied by a kink in the carbon backbone and at the end of a line
what are haloalkanes
substituted alkanes in which one or more of the hydrogen atoms is replaced with a halogen atom
what is a monohaloalkane
these contain only one halogen atom, can be classified as primary, secondary or tertiary according to the number of alkyl groups attached to the carbon atom containing the halogen atom.
what do monohaloalkanes take part in elimination reactions to form
alkenes using a strong base, such as potassium, or sodium hydroxide in ethanol.
what are the nucleophilic substitution reactions that monohaloalkanes take part in
- aqueous alkalis to form alcohols
- alcoholic alkoxides to form ethers
- ethanoic cyanide to form nitriles that can be hydrolysed to carboxylic acids
what are the different mechanisms that monohaloalkanes can take part in nucleophilic substitution reactions by
Sn1 and Sn2
what is the Sn1 mechanism
a nucleophilic substitution reaction with one species in the rate determining step. occurs in a minimum of two steps via a trigonal planar carbocation intermediate
what is the Sn2 mechanism
a nucleophilic substitution reaction with two species in the rate determining step. occurs in a single step via a single five centred trigonal bipyramidal transition state
what is a steric hindrance
the slowing of chemical reactions due to steric bulk. steric iss the arrangement of atoms in space
what is inductive stabilisation
the stability of a molecule depending on the charge present on the atom and the groups bonded to the atom
how can alcohols be prepared
from haloalkanes by substitution
from alkenes by acid catalysed hydration
aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride
what makes alcohols polar
the hydroxyl groups
what are ethers regarded as
substituted alkanes in which a hydrogen atom is replaced by an alkoxy functional group
what is the alkoxy functional group
-OR
how can ethers be prepared
in a nucleophilic substitution reaction by reacting a monohaloalkane with an alkoxide
why do ethers have lower boiling points than the corresponding isomeric alcohols
due to the lack of hydrogen bonding between the molecules
why are larger ethers insoluble in water
due to their increased molecular size
what are examples of soluble ethers
methoxymethane and methoxyethane
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 are the electrophilic addition reactions that alkenes take part with
hydrogen to form alkanes in the presence of a catalyst
halogens to form dihaloalkanes
hydrogen halides to form monohaloalkanes
water using an acid catalyst to form alcohols
what does markovnikov’s rule state
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 attached to it already. this rule can be used to predict major and minor products formed during the reaction of a hydrogen halide or water with alkenes
how can carboxylic acids be prepared
by oxidising primary alcohols using acidified permangenate, acidified dichromate, fehling’s solution and tollen’s reagent
hydrolysing nitriles, esters or amides
what are examples of reactions involving carboxylic acids
- formation of salts by reactions with metals or bases
- condensation reactions with alcohols to form esters in the presence of concentrated sulfuric or concentrated phosphoric acid
- reaction with amines to form alkylammonium salts that form amides when heated
- reduction with lithium aluminium hydride to form primary alcohols
what are amines
organic derivatives of ammonia in which one of more hydrogen atoms of ammonia has been replaced by an alkyl group. they can be classified as primary, secondary or tertiary according to the number of alkyl groups attached to the nitrogen atom
what do amines react with the form salts
acids
which type of amines display hydrogen bonding
primary and secondary
why do primary and secondary amines have higher boiling points than isomeric tertiary amines
they display hydrogen bonding
are amines weak bases, and what does this imply
yes, and it means they dissociate partially in solution.
how do amines produce hydroxide ions
the nitrogen atom has a lone pair of electrons which can accept a proton from water
what is the simplest member of the class of aromatic hydrocarbons
benzene
why are benzene rings stable
due to the delocalisation of electrons in the conjugated system - this is why they do not take part in addition reactions
how can bonding in benzene be explained
in terms of sp2 hybridisation, sigma and pi bonds, and electron delocalisation
what is a benzene ring
this is when one hydrogen atom has been subsituted by a phenyl group
what is the formula for a phenyl group
C6H5
what is the formula for a phenyl group
C6H5
what do reactions at benzene rings include
- halogenation by reaction of a halogen using alumium chloride or iron chloride for chlorination and aluminium bromide or iron 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
