Revision Flashcards
What is Bond fission?
When an organic reaction takes place, bonds in the reactant molecules are broken and
bonds in the product molecules are made. The process of bond breaking is known as bond
fission.
What is Homolytic bond 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
- Requires UV to do so
What is heterolytic bond fission?
- results in the formation of two oppositely charged ions
- occurs when one atom retains both electrons from the sigma covalent bond and the bond
breaks unevenly - normally occurs when polar covalent bonds are broken
How is Homolytic bond fission indicated?
two single-headed arrows starting at the middle of a covalent bond indicate homolytic bond fission is occurring
How is heterolytic bond fission indicated?
two double-headed arrow starting at the middle of a covalent bond indicates heterolytic bond fission is occurring
What do double headed arrows indicate?
a double-headed arrow indicates the movement of an electron pair
What do single headed arrow indicate?
a single-headed arrow indicates the movement of a single electron
What are nucleophiles?
- negatively charged ions or neutral molecules that are electron rich
- attracted towards atoms bearing a partial positive or full positive charge
- capable of donating an electron pair to form a new covalent bond
What are some examples of nucleophiles?
Chloride ion, bromide ion, hydroxide ion, cyanide ion, ammonium and water
What are electrophiles?
- positively charged ions or neutral molecules that are electron deficient
- attracted towards atoms bearing a partial or full negative charge
- capable of accepting an electron pair to form a new covalent bond
What is skeletal formula?
In a skeletal structural formula, neither the carbon atoms, nor any hydrogens attached to the carbon atoms, are shown
What are haloalkanes?
Haloalkanes (alkyl halides) are substituted alkanes in which one or more of the hydrogen
atoms is replaced with a halogen atom
What are 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 is SN1?
- nucleophilic substitution reaction
- one species in the rate determining step
- occurs in a minimum of two steps
- via a trigonal planar carbocation intermediate.
What is SN2?
- nucleophilic substitution reaction
- two species in the rate determining step
- occurs in a single step
- via a single five-centred, trigonal bipyramidal transition state
What is the inductive effect?
- ALKYL Positive inductive effect
- Electron donating and push electrons towards the positive charge on the carbon which helps to stabilise it.
What is steric effect?
- The size of the alkyl groups causes the steric effect
- In SN2 the nucleophile attacks from the side opposite the halogen
- Tertiary haloalkanes resist this attack as it is sterically hindered as the three bulky alkyl groups prevent access to the positive carbon
What is more likely to undergo SN1?
Tertiary haloalkanes
What is more likely to undergo SN2?
Primary monohaloalkanes
What are 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 the hydroxyl group of an alcohol allow?
Hydroxyl groups make alcohols polar, which gives rise to hydrogen bonding
What are ethers?
- Ethers can be regarded as 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
Why do ethers have lower boiling points than alcohols?
Due to the lack of hydrogen bonding between ether molecules, they have lower boiling points than the corresponding isomeric alcohols
How are ethers named?
Ethers are named as substituted alkanes. The alkoxy group is named by adding the ending ‘oxy’ to the alkyl substituent, and this prefixes the name of the longest carbon chain.
Why are large ethers insoluble in water?
Larger ethers are insoluble in water due to their increased molecular size
Why are ethers used as solvents?
Ethers are commonly used as solvents since they are relatively inert chemically and will dissolve many organic compounds.
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
- used to predict major and minor products formed during the reaction of a hydrogen halide or water with alkenes
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?
Amines can be classified as primary, secondary or tertiary according to the number of alkyl groups attached to the nitrogen atom.
What type of amines display hydrogen bonding and what does it result in?
- Primary and secondary amines
- As a result, primary and secondary amines have higher boiling points than isomeric tertiary
amines.
Why are shorter amines soluble in water?
Primary, secondary and tertiary amine molecules can hydrogen-bond with water molecules,
thus explaining the appreciable solubility of the shorter chain length amines in water
Why can amines produce hydroxide ions?
Amines like ammonia are weak bases and dissociate to a slight extent in aqueous solution. The nitrogen atom has a lone pair of electrons which can accept a proton from water, producing hydroxide ions.
What is benzene?
- Benzene (C6H6) is the simplest member of the class of aromatic hydrocarbons.
Why is benzene stable?
The stability of the benzene ring is due to the delocalisation of electrons in the conjugated system.
Why does benzene not take part in electrophilic addition reactions?
The presence of delocalised electrons
What are some examples of electrophiles?
hydrogen ions, nitrous oxide ions and sulfur trioxide
