3.2 Synthesis Flashcards
types of bond fission
- homolytic
- heterolytic
- homolytic
- heterolytic
types of bond fission
bond fission
bond breaking
homolytic fission
- results in the formation of two neutral radicals
- occurs when each atom retains one electron from the sigma covalent bond and the bond
breaks evenly - normally occurs when non-polar covalent bonds are broken
- tend to result in the formation of very complex mixtures of products, making them unsuitable for organic synthesis
- results in the formation of two neutral radicals
- occurs when each atom retains one electron from the sigma covalent bond and the bond
breaks evenly - normally occurs when non-polar covalent bonds are broken
- usually to result in the formation of very complex mixtures of products, making them unsuitable for organic synthesis
homolytic fission
heterolytic fission
- results in the formation of two oppositely charged ions
- occurs when one atom retains both electrons from the σ covalent bond and the bond breaks unevenly
- normally occurs when polar covalent bonds are broken
- usually result in far fewer products than reactions involving homolytic fission, and so are better suited for organic synthesis
- results in the formation of two oppositely charged ions
- occurs when one atom retains both electrons from the σ covalent bond and the bond breaks unevenly
- normally occurs when polar covalent bonds are broken
- usually result in far fewer products than reactions involving homolytic fission, and so are better suited for organic synthesis
heterolytic fission
what are attacking groups classified as in reactions involving heterolytic bond fission
- nucleophiles
- electrophiles
when are groups classified as nucleophiles or electrophiles
if they are an attacking group in heterolytic bond fission
nucleophile
- negatively charged ions or neutral molecules that are electron rich, such as
Cl−, Br−, OH−, CN− , NH3 and H2O - attracted towards atoms bearing a partial (δ+) or full positive charge
- capable of donating an electron pair to form a new covalent bond
- negatively charged ions or neutral molecules that are electron rich, such as
Cl−, Br−, OH−, CN− , NH3 and H2O - attracted towards atoms bearing a partial (δ+) or full positive charge
- capable of donating an electron pair to form a new covalent bond
nucleophiles
electrophile
- positively charged ions or neutral molecules that are electron deficient, such as H+,NO2+ and SO3
- attracted towards atoms bearing a partial (δ−) or full negative charge
- capable of accepting an electron pair to form a new covalent bond
- positively charged ions or neutral molecules that are electron deficient, such as H+,NO2+ and SO3
- attracted towards atoms bearing a partial (δ−) or full negative charge
- capable of accepting an electron pair to form a new covalent bond
electrophile
haloalkane
- aka alkyl halides
- substituted alkanes in which one or more of the H atoms is replaced with a halogen atom
- aka alkyl halides
- substituted alkanes in which one or more of the H atoms is replaced with a halogen atom
haloalkane
monohaloalkane
- 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
- take part in elimination reactions to form alkenes using a strong base, such as potassium or sodium hydroxide in ethanol
- take part in nucleophilic substitution reactions with:
— aqueous alkalis to form alcohols
— alcoholic alkoxides to form ethers
— ethanolic cyanide to form nitriles (chain length increased by one carbon atom) that can be hydrolysed to carboxylic acids - can take part in nucleophilic substitution by one of two mechanisms: sn1 or sn2
mechanisms for monoalkanes in nucleophilic substitution
- sn1: nucleophilic substitution reaction with one species in the rate determining step and occurs in a minimum of two steps via a trigonal planar carbocation intermediate
- sn2: nucleophilic substitution reaction with two species in the rate determining step and occurs in a single step via a single five-centred, trigonal bipyramidal transition state
- sn1: nucleophilic substitution reaction with one species in the rate determining step and occurs in a minimum of two steps via a trigonal planar carbocation intermediate
- sn2: nucleophilic substitution reaction with two species in the rate determining step and occurs in a single step via a single five-centred, trigonal bipyramidal transition state
mechanisms for monoalkanes in nucleophilic substitution
alcohol
substituted alkanes in which one or more of the hydrogen atoms is replaced with a hydroxyl group, OH-
substituted alkanes in which one or more of the hydrogen atoms is replaced with a hydroxyl group, OH-
alcohol
what can alcohols be prepared from
- haloalkanes by substitution
- alkenes by acid-catalysed hydration (addition)
- aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride
what can be prepared from the following
- haloalkanes by substitution
- alkenes by acid-catalysed hydration (addition)
- aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride
alcohols
reactions of alcohols
- dehydration to form alkenes using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
- oxidation of primary alcohols to form aldehydes and then carboxylic acids and secondary alcohols to form ketones, using acidified permanganate, acidified dichromate or hot copper(II) oxide
- formation of alcoholic alkoxides by reaction with some reactive metals such as potassium or sodium, which can then be reacted with monohaloalkanes to form ethers
- formation of esters by reaction with carboxylic acids using concentrated sulfuric acid or concentrated phosphoric acid as a catalyst
- formation of esters by reaction with acid chlorides ( R-COCl) — this gives a faster reaction than reaction with carboxylic acids, and no catalyst is needed
- dehydration to form alkenes using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
- oxidation of primary alcohols to form aldehydes and then carboxylic acids and secondary alcohols to form ketones, using acidified permanganate, acidified dichromate or hot copper(II) oxide
- formation of alcoholic alkoxides by reaction with some reactive metals such as potassium or sodium, which can then be reacted with monohaloalkanes to form ethers
- formation of esters by reaction with carboxylic acids using concentrated sulfuric acid or concentrated phosphoric acid as a catalyst
- formation of esters by reaction with acid chlorides ( R-COCl) — this gives a faster reaction than reaction with carboxylic acids, and no catalyst is needed
reactions of alcohols
hydroxyl group and polarity
- hydroyl groups make alcohol polar
- this gives rise to hydrogen bonding
- hydrogen bonding can be used to explain the properties of alcohols, including BP, MP, viscosity, and solubility in water
ethers
substituted alkanes in which a hydrogen atom is replaced with an alkoxy functional group, -OR, and have the general structure R’-O-R’’, where R’ and R’’ are alkyl groups
substituted alkanes in which a hydrogen atom is replaced with an alkoxy functional group, -OR, and have the general structure R’-O-R’’, where R’ and R’’ are alkyl groups
ether
what can ethers be prepared from
nucleophilic substitution reaction by reacting a monohaloalkane with an alkoxide
what is prepared from a nucleophilic substitution reaction by reacting a monohaloalkane with an alkoxide
ether
ethers and isomeric alcohols BP
- ethers have lower BPs than isomeric alcohols
- this is due to the lack of hydrogen bonding
solubility of ethers in water
- methoxymethane and methoxyethane are soluble in water
- larger ethers are insoluble in water due to their increased molecular size
ethers use
commonly used as solvents since they are relatively inert chemically and will dissolve many organic compounds
what are commonly used as solvents since they are relatively inert chemically and will dissolve many organic compounds
ethers
how to prepare alkenes
- dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
- base-induced elimination of hydrogen halides from monohaloalkanes
what can be prepared from:
- dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid
- base-induced elimination of hydrogen halides from monohaloalkanes
alkenes
alkene reactions
- 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
- 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
alkene reactions
Markovnikov’s rule
- 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
- 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
Markovnikov’s rule
how to prepare carboxylic acid
- 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
what can be prepared from he following:
- 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
carboxylic acid
reactions of 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
- 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
reactions of carboxylic acids
amine
- organic derivative of ammonia in which one or more hydrogen atoms of ammonia has been replaced by an alkyl group
- can be classified as primary, secondary, or tertiary, according to the number of alkyl groups attached to the nitrogen atom
- organic derivative of ammonia in which one or more hydrogen atoms of ammonia has been replaced by an alkyl group
- can be classified as primary, secondary, or tertiary, according to the number of alkyl groups attached to the nitrogen atom
amines
amine reaction
reacts with acids to from salts
what reacts with acids to from salts
amines
amines intermolecular bonding
- primary and secondary amines, but not tertiary amines, display H bonding. Thus they have higher BPs than isomeric tertiary amines
- primary, secondary and tertiary amine molecules can hydrogen-bond with water molecules
- this explains the appreciable solubility of the shorter chain length amines in water
- primary, secondary and tertiary amine molecules can hydrogen-bond with water molecules
- this explains the appreciable solubility of the shorter chain length amines in water
amines solubility in water
Amine in water
- amines like ammonia are weak bases and dissociate to a slight extent in aqueous solutions
- the N atom has a lone pair of electrons which can accept a proton from water, producing hydroxide ions
- _____ like ammonia are weak bases and dissociate to a slight extent in aqueous solutions
- the N atom has a lone pair of electrons which can accept a proton from water, producing hydroxide ions
Amines
Aromatic hydrocarbons
Benzene (C6H6)
Benzene (C6H6)
Simplest member of the class of aromatic hydrocarbons
Benzene ring structural formula
- The benzene ring has a distinctive structural formula
- The stability of the benzene ring is due to the delocalisation of electrons in the conjugated system
- The presence of delocalised electrons explains why the benzene ring does not take part in addition reactions
Phenyl group
- Benzene ring in which one H atom has been substituted by another group, this is known as the phenyl group
- Has the formula -C6H5
- Benzene ring in which one H atom has been substituted by another group, this is known as the phenyl group
- Has the formula -C6H5
Phenyl group
Benzene ring reactions
Can take part in electrophilic substation reactions. This includes:
- halogenating 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 sulphuric acid and concentrated nitric acid
- sulfonation using concentrated sulphuric acid
Can take part in electrophilic substation reactions. This includes:
- halogenating 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 sulphuric acid and concentrated nitric acid
- sulfonation using concentrated sulphuric acid
Benzene reactions
