Synthesis

What is the process of bond breaking known as?

Bond fission

What are the two types of bond fission?

• Homolytic

• Heterolytic

Describe Homolytic fission.

Homolytic fission results in the formation of two neutral radicals. This normally occurs when each atom retains one electron from the covalent bond and the bond breaks evenly. It normally occurs when non-polar covalent bonds are broken.

What do reactions involving homolytic fission tend to result in?

Tent to result in the formation of very complex mixtures of products —> making them unsuitable for organic synthesis

Describe Heterolytic fission.

Heterolytic fission results in the formation of two oppositely charged ions. This occurs when one atom retains both electrons from the sigma (o-) covalent bond and the bond breaks unevenly. It normally occurs when polar covalent bonds are broken.

What do reactions involving Heterolytic fission tend to result in?

Tend to result in far fewer products than reactions involving homolytic fission —> better suited for organic synthesis

How is the movement of electrons during bond fission and bond making represented?

Using curly arrow notation.

In reactions involving Heterolytic bond fission, attacking groups are classified as … ?

Nucleophiles or electrophiles

Give the definition of a nucleophile.

Nucleophiles are negatively charged ions or neutral molecules that are electron rich.

What are examples of Nucleophiles?

Cl-, Br-, OH-, CN-, NH3, H20

What are Nucleophiles attracted to?

Towards atoms bearing a partial (&+) or full positive charge. They are capable of donating an electron pair to form a new covalent bond.

Give the definition of Electrophiles.

Electrophiles are positively charged ions or neutral molecules that are electron deficient.

Give examples of Electrophiles.

H+, NO2+, S03

What are electrophiles attracted towards?

Atoms bearing a partial (&-) or full negative charge. They are capable of accepting an electron pair to form a new covalent bond.

What is a substitution reaction?

A substitution reaction is one in which an atom or group of atoms is replaced by another atom or group of atoms.

What is an addition reaction?

An addition reaction is a reaction in which two molecules join together to make one larger molecule.

What is an elimination reaction?

An elimination reaction is one in which a small molecule is removed from an organic compound.

ALKENES

Describe alkenes.

Unsaturated hydrocarbons (C=C)

How can alkenes be prepared?

By dehydration of alcohols using aluminium oxide, concentrated sulfuric acid or concentrated phosphoric acid. They can also be prepared by base-induced elimination of hydrogen halides from monohaloalkanes.

State what Markovnikov’s rule is.

Is that when a hydrogen halide or water is added to an asymmetric alkene, the hydrogen atom becomes attached to the carbon with the most hydrogen atoms attached to it already.

What is Markovnikov’s rule used to predict?

The major and minor products formed during the reaction of a hydrogen halide or water with alkenes.

What do alkenes take part in electrophilic addition reactions with?

• Hydrogen to form alkanes in the presence of a catalyst (Hydrogenantion)

• Halogens to form dihaloalkanes (Halogenation)

• Hydrogen halides to form monohaloalkanes (Hydrohalogenation)

• Water using an acid catalyst to form alcohols (Hydration)

Explain Haloalkanes. (alkyl halides)

Haloalkanes (alkyl halides) are substituted alkanes where one or more of the hydrogen atoms is substituted with a halogen atom.

Explain Monohaloalkanes.

• 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 type of reactions do monohaloalkanes take part in?

• They 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:

  • 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

What are the two different mechanisms that monohaloalkanes undergo nucleophilic substitution reactions by?

• Sn1 —> is a nucleophilic substitution reactions with one species in the rate determining step and occurs in a minimum of two steps via a trigonal planar carbocation intermediate.

• Sn2 —> is a nucleophilic substitution reactions with two species in the rate determining step and occurs in a single step via a single five-centred, trigonal bipyramidal transition state.

Explain the steric hindrance effect.

The prevention or slowing down of a reaction by atoms or functional groups blocking the access of an attacking molecule or ion.

Explain the inductive effect.

Effect of a functional groups or atom in an organic molecule which attracts sigma electrons towards itself, or repels them, resulting in the formation of a dipole in the molecule.

What is the order of stability of carbocation?

Primary < secondary < tertiary

ALCOHOLS

Explain Alcohols.

Alcohols are substituted alkanes in which one or more of the hydrogen atoms is replaced with a hydroxyl functional group, -OH group.

What does hydroxyl groups make alcohols?

Hydroxyl groups make alcohols polar, which gives rise to hydrogen bonding.

How are alcohols prepared?

• Haloalkanes by substitution

• Alkenes by acid-catalysed hydration (addition)

• Aldehydes and ketones by reduction using a reducing agent such as lithium aluminium hydride

What are the 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 - this gives a faster reaction than reaction with carboxylic acids, and no catalyst is needed.

What are ethers?

Ethers can be regarded as substituted alkanes in which a hydrogen atom is replaced with an alkoxides functional groups, -OR, and have the general structure R’ - O - R”, where R’ and R” are alkyl groups.

How can ethers be prepared?

Ethers can be prepared in a nucleophilic substitution reaction by reacting a monohaloalkanes with an alkoxides.

Why do ethers have lower boiling points than the corresponding isomeric alcohols?

Due to the lack of hydrogen bonding between ether molecules.

Are large ethers insoluble or soluble in water? Explain.

Larger ethers are insoluble in water due to their increased molecular size.

What are ethers commonly used as?

Solvents, since they are relatively inert chemically and will dissolve many organic compounds.

CARBOXYLIC ACIDS

How can carboxylic acids be prepared?

• Oxidising primary alcohols using acidified permanganate, acidified dichromate and hot copper (II) oxide.

• Oxidising aldehydes using acidified permanganate, acidified dichromate, Fehling’s solution and Tolllens’ reagent

• Hydrolysing nitriles, esters or amides

What are 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 alkyl ammonium salts that form amides when heated

• Reduction with lithium aluminium hydride to form primary alcohols.

What are amines?

Amines are organic derivatives of ammonia in which one or more hydrogen atoms of ammonia has been replaced by an alkyl group.

How can amines be classified?

As primary, secondary, or tertiary (depending on the number of alkyl groups attached to the nitrogen atom)

What do amides react with to form salts?

Acids

Which amines display hydrogen bonding?

Primary and secondary —> therefore have higher boiling points than isometric tertiary amines.

What are amines like ammonia?

Weak bases and dissociate to a slight extent in aqueous solution.

What is benzene (C6H6)?

The simplest member of the class of aromatic hydrocarbons.