(b) synthesis Flashcards
What is the process of bond breaking known as?
Bond fission.
How many types of fission are there?
2
What are the names of the two types of fission?
Homolytic and hetrolytic.
What does homolytic fission result in?
The formation of 2 neutral free radicals.
Why does homolytic fission result in free radicals?
When each atom retains one electron from the sigma covalent bond and the bond breaks evenly.
What type of bond is usually broken when homolytic fission occurs?
Non-polar covalent bonds.
Why do reactions involving homolytic fission result in mixtures which are unsuitable for organic synthesis?
The resulting mixtures are formed of very complex mixtures of products.
What does heterolytic fission result in the creation of?
Two oppositely charged ions.
Why does heterolytic fissions create ions?
One atom retains both electrons from the sigma covalent bond and the bond breaks unevenly.
What type of bond is usually broken when heterolytic fission occurs?
Polar covalent bonds.
Why are the products of reactions involving heterolytic fission much better suited for organic synthesis?
There tends to be far fewer products than reactions involving homolytic fission.
What are the attacking groups involved in heterolytic fission called?
Nucleophiles and electrophiles.
What are nucleophiles?
Negatively charged ions or neutral molecules that are electron rich.
What is an example of a nucleophile?
Chlorine ion, bromine ion, water, e.c.t.
What are nucleophiles attracted to?
Atoms bearing a partial or full positive charge.
What are nucleophiles capable of doing?
Donating an electron pair to form a new covalent bond.
What are electrophiles?
Positively charged ions or neutral molecules which are electron deficient.
What is an example of an electrophile?
Hydrogen ion, nitrogen oxide e.c.t.
What are electrophiles attracted to?
Atoms bearing a partial or full negative charge.
What are electrons capable of doing?
Accepting an electron pair to form a new covalent bond.
What is a haloalkane?
Substituted alkanes in which one or more of the hydrogen atoms is replaced with a halogen atom.
How many halogen atoms are in a monohaloalkane?
1
Can monohaloalkanes take part in elimination reactions?
Yes.
What must be present for monohaloalkanes to undergo elimination reactions?
A strong base.
Give an example of a strong base.
Potassium or sodium hydroxide in ethanol.
What other reactions can monohaloalkanes take part in?
Nucleophilic substitution.
If a monohaloalkane undergoes nucleophilic substitution with an aqueous alkali what is formed?
Alcohol.
If a monohaloalkane undergoes nucleophilic substitution with a alcoholic alkoxides what is formed?
Ether.
If a monohaloalkane undergoes nucleophilic substitution with ethanolic cyanide what is formed?
Nitriles.
What happens to the chain length when a monohaloalkane undergoes nucleophilic substitution to become a nitrile?
The chain length increases by one carbon atom.
What can happen to this nitrile?
It can be hydrolysed to become a carboxylic acid.
What is reacted with a mono halo alkane to form an alcohol?
aqueous alkali.
What is reacted with a mono halo alkane to form ethers?
alcoholic alkoxides.
What is reacted with a mono halo alkane to form nitriles?
Ethanolic cyanide.
What is SN1 substitution?
A 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.
What is SN2 substitution?
A nucleophilic substitution reaction with two species in the rate determining stipend occurs in a single step via a single 5 centred trigonal bipyramidal transition state.
What types of molecules undergo SN1 substitution?
Tertiary and sometimes secondary haloalkanes.
Why do only tertiary and sometimes secondary haloalkanes undergo SN1 substitution?
Because there is no room for a nucleophile to attack the central carbon.
What is this blocking effect known as?
Steric hindrance.
what types of molecules undergo SN2 substitution?
Primary and sometimes secondary haloalkanes.
Why can only primary and sometimes secondary haloalkanes undergo SN2 substitution?
Because there is less steric hinderance.
Where does the nucleophile attack from in SN2?
The opposite side to the halogen.
What type of molecule undergoes substitution to form alcohols?
Alkanes.
How else can alcohols be prepared?
alkenes by acid-catylised hydration
the reduction of aldehydes and ketones using a reducing agent.
What is an example of a reducing agent which would allow the reduction of aldehydes and ketones into alcohols to take place?
Lithium aluminium hydride.
What does an alcohol dehydrate to form?
Alkenes.
What is used to dehydrate alcohols to produce alkenes?
Aluminium oxide
Concentrated sulphuric acid
Concentrated phosphoric acid.
How are alkenes formed from alcohols?
Through dehydration with aluminium oxide, concentrated sulphuric acid, or concentrated phosphoric acid.
What does a primary alcohol oxidise to form?
An aldehyde.
What do aldehydes oxidise to form?
Carboxylic acids.
What do secondary alcohols oxidise to form?
Ketones.
What are alcohols oxidised with to form aldehydes and ketones?
Acidified potassium permanganate
Acidified dichromate
Hot copper (II) oxide.
How are aldehydes and ketones formed from alcohols?
Through oxidation of a primary, to become an aldehyde, or secondary, to become a ketone, alcohol with acidified potassium permanganate, acidified dichromate, or hot copper (II) oxide.
When alcohols react with some reactive metals what is formed?
alcoholic alkoxides.
What reactive metals react with alcohols to form alcoholic alkoxides?
Potassium or Sodium.
What can alcoholic alkoxides then react with to produce a different molecule?
Monohaloalkanes to form ethers.
How are alcoholic alkoxides produced from alcohol?
Alcohols react with some reactive metals such as sodium or potassium.
Alcohols react with carboxylic acids to form what?
Esters.
What are alcohols and carboxylic acids reacted with to form esters?
Sulphuric acid
Phosphoric acid
What does phosphoric and sulphuric acid act as in the reaction between an alcohol and a carboxylic acid?
A catalyst.
How are esters produced from alcohols?
By reacting alcohols with carboxylic acids using concentrated sulphuric acid or concentrated phosphoric acid as a catalyst.
What is a faster way to create esters without using a catalyst?
Reacting alcohols with acid chlorides.
What do hydroxyl groups make alcohols?
Polar.
What does polar bonds give rise to?
Hydrogen bonding.
What can hydrogen bonding be used to explain?
The properties of alcohols.
What can ethers be regarded as?
substituted alkanes.
How are ethers named?
By adding alkoxy to prefix the longest carbon chain.
How can ethers be produced?
Through nucleophilic substitution reaction by reacting a monohaloalkane with an alkoxide.
Do ethers have higher or lower boiling points compared to the isomeric alcohols?
Lower.
Why do ethers have lower boiling points compared to the corresponding isomeric alcohols?
Lack of hydrogen bonding in ethers.
Are ethers soluble or insoluble in water?
The first two ethers are soluble in water, however larger ethers are insoluble due to their increased molecular size.
Why are ethers commonly used as solvents?
They are relatively inert and will dissolve many organic compounds.
How can alkenes be prepared from alcohols?
Dehydration of alcohols using aluminium oxide, concentrated sulphuric acid or concentrated phosphoric acid.
How else can alkenes be prepared?
Base-induced elimination of hydrogen halides from monohaloalkanes.
Alkenes take part in electrophilic addition with what?
Hydrogen
Hydrogen halides
Water
What is formed when alkenes undergo electrophilic addition with hydrogen in the presence of a catalyst?
Alkanes.
What is produced when alkenes undergo electrophilic addition with hydrogen not in the presence of a catalyst?
Dihaloalkanes.
What is formed when alkenes undergo electrophilic addition with hydrogen halides?
Monohaloalkanes.
What is produced when alkenes undergo electrophilic addition with water using an acid catalyst?
Alcohols.
What is required for alkenes to produce alcohols?
Acid catalyst.
What does Markovnikovs’ 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.
What can Markovnikovs’ rule predict?
Major and minor products.
How are carboxylic acids produced from primary alcohols?
Oxidation using potassium permanganate, acidified potassium dichromate, and hot copper (II) oxide.
How are carboxylic acid produced from aldehydes?
Oxidation using acidified permanganate, acidified dichromate, Fehling’s solution, or Tollens’ reagent.
How are carboxylic acids produced from nitriles, esters or amides?
Hydrolising.
What is formed when carboxylic acids react with metals or bases?
Salts.
How are salts formed from carboxylic acids?
By reacting carboxylic acids with metals or bases.
How are Esthers formed from carboxylic acids?
Condensation reactions with alcohol.
What must be present for the condensation reaction with alcohol for Esthers to be made?
Concentrated sulphuric acid
Concentrated phosphoric acid.
When carboxylic acids react with amines what is formed?
Alkyl ammonium salts.
How are alkyl ammonium salts created?
Through the heating of amides.
What is formed when carboxylic acids are reduced with lithium ammonium hydride?
Primary alcohols.
What must be present for carboxylic acids to be reduced into primary alcohols?
Lithium ammonium hydride.
What amines organic derivatives of?
Ammonia.
How do amines and ammonia differ?
One or more of the hydrogen atoms has been replaced with an alkyl group.
When amines react with acids what is formed?
Salts.
What kind of amines show hydrogen bonding?
Primary and secondary amines.
What kinds of amines have the highest melting and boiling points?
Primary and secondary.
Can all amines hydrogen bond with water?
Yes.
Why are smaller amines more soluble in water?
Hydrogen bonding.
What makes amines similar to ammonia?
They are both weak bases.
What happens to both amines and ammonia in water?
They dissociate.
How are hydroxide ions produced from amines and ammonia in water?
The nitrogen atom has a lone pair of electrons which can accept a proton from water producing hydroxide ions.
What is the simplest member of the aromatic hydrocarbons?
Benzene.
What is benzenes formula?
C6H6
What is the stability of benzene due to?
The delocalisation of electrons in the conjugated system.
Why does benzene not take part in any addition reaction?
The presence of delocalised electrons.
How can bonding in benzene be described?
Sp2 hybridisation, sigma and pi bonds, and electron delocalisation.
What is it called when in a benzene ring one hydrogen atom has been substituted by another group?
The phenyl group.
What is the formula of the phenyl group?
C6H5.
How does benzene undergo halogenation?
The addition of a halogen using aluminium chloride, or iron(III) chloride for chlorination, and aluminium bromide or iron (III) bromide for bromination.
How does benzene undergo alkylation?
By reaction of a haloalkane using aluminium chloride.
How does benzene undergo nitration?
Using concentrated sulphuric acid and concentrated nitric acid.
How does benzene undergo sulfonation?
Using concentrated sulphuric acid.
