General Questions - Alkanes and Alkenes Flashcards
What type of reaction makes a di-ol?
Oxidation
What are free radicals?
Species with an unpaired electron
What is a homologous series?
Organic compounds with the same functional group and general formula
What do curly arrows show in a mechanism diagram?
Curly show arrows show where a pair of electrons go during a reaction when bonds are made or broken
Mechanism: … of halogens in alkanes, to make halogenoalkanes
Radical substitution
Mechanism: … of halogens and hydrogen halides to alkenes to make halogenoalkanes
Electrophilic addition
Mechanism: … of primary halogenoalkanes with aqueous potassium hydroxide to make alcohols
Nucleophilic substitution
Mechanism: … of primary halogenoalkanes with ammonia to make amines
Nucleophilic substitution
Do nucleophiles give or take pairs of electrons?
Nucleophiles are electron pair donors
Do electrophiles give or take pairs of electrons?
Electrophiles are electron pair acceptors
What is the charge of a nucleophile?
Negative
What is the charge of an electrophile?
Positive
Which places are nucleophiles attracted to and why?
Nucleophiles are attracted to places that are electron poor because they are electron rich.
Which places are electrophiles attracted to and why?
Electrophiles are attracted to places that are electron rich because they are electron poor.
Which type of molecules are attached by nucleophiles?
Molecules with polar bonds
What is it called when nucleophiles are attracted to the Cδ+ atom in a polar carbon-halogen bond?
Nucleophilic substitution
In a molecule with a polar bond, the Hδ acts as a what and is strongly attracted to what?
The Hδ acts as an electrophile and is strongly attracted to the C=C double bond
Radicals will react to molecules with what charge: positive, negative or neutral?
Radicals will react with anything positive, negative or neutral as they are very, very reactive.
What are the relationships between the chemical and physical properties of chain isomers?
They have:
• similar chemical properties
• different physical properties
What are the relationships between the chemical and physical properties of positional isomers?
They have:
• different physical properties
• (maybe) different chemical properties
What are the relationships between the chemical and physical properties of functional isomers?
They have:
• very different physical properties
• very different chemical properties
Are alkanes saturated or unsaturated hydrocarbons?
Saturated
Give the general formula for an alkane.
Cn H2n+2
What is bond fission?
The breaking of a covalent bond
How do bonds break in heterolytic fission?
The bond breaks unevenly with one of the bonded atoms
• two different substances can be formed
How do bonds break in homolytic fission?
Bonds break evenly
• each bonding atom receives one electron from bonded pair
• two electrically uncharged ‘radicals’ are formed
How are radicals shown in mechanisms?
The have a big dot next to the molecular formula
What are halogens?
Halogens are the highly reactive non-metals of group 7
Halogens reacts with what substance in photochemical reactions?
Alkanes
What are photochemical reactions?
Reactions started by light - requires ultraviolet light
What are the three stages of the reaction of halogens with alkanes to form halogenoalkanes?
Initiation, propitiation and termination
What is photodissociation?
When sunlight provides enough energy to break a bond.
Reaction of halogens with alkanes to form halogenoalkanes:
What type of fission occurs during initiation?
Homolytic fission - bond splits equally and each atom gets to keep one electron
Reaction of halogens with alkanes to form halogenoalkanes:
What words can be used to describe the atom after imitation has occurred?
- Highly reactive
* Radical
Reaction of halogens with alkanes to form halogenoalkanes: give a summary of what events occur during propagation?
Radicals are used up and created in a chain reaction
Reaction of halogens with alkanes to form halogenoalkanes: what happens to the radicals during termination?
The radicals are destroyed as they react together to form a stable molecule
What do two free radicals make if they join together?
They make a stable molecule
Reaction of halogens with alkanes to form halogenoalkanes: what is the best way to avoid producing a mixture of products?
Using an excess of methane
When do covalent bonds form?
Covalent bonds form when:
• atomic orbitals (each containing a single electron) overlap
• electrons become shared
Why do covalent bonds form?
The nuclei of the atoms are attracted by electrostatic attraction to the bonding electrons
What type of bonds are single covalent bonds in organic molecules?
Sigma bonds
High electron density between nuclei means what?
Strong electrostatic attraction between nuclei and shared pair of electrons
Do sigma bonds have a high or low bond enthalpy?
High
What bonds is a double made up of?
A sigma bond and a pi bond
When does a pi bond form?
When two lobes of two orbitals overlap sideways
What are the two parts to a pi bond?
- the part ‘above’ the molecular axis
* the part ‘below’ the molecular axis
Do pi bonds have a high or low bond enthalpy?
Low
Adding hydrogen halides to unsymmetrical alkenes form how many products?
Two
Are carbocations with more alkyl groups, more or less stable?
More stable
What are the two products of the reaction of hydrogen bromide and propene?
- 2-bromopropane
* 1-bromopropane
What is Markownikoff’s rule?
The major product from the addition of a hydrogen halide to an unsymmetrical alkene is the one where hydrogen adds to the carbon with the most hydrogens already attached.
What does the reaction of ethene to hydrogen in a gas addition need?
- a temperature of 150°c
* a nickel catalyst
What can increase the melting point in the process of making margarine?
Removing double bonds
Halogens react with alkenes to form what in what type of reaction?
Dihalogenoalkanes through electrophilic addition
When you shake an alkene with brown bromine water, what happens to the solution?
The solution decolourises
What are alkenes oxidised by?
Potassium manganate (VII)
What are halogenoalkanes?
Alkanes with halogen atoms in place of a hydrogen atom is
What is the structure of a primary halogenoalkane?
A primary halogenoalkane has:
• two hydrogen atoms
• one alkyl group
What is the structure of a secondary halogenoalkane?
A secondary halogenoalkane has:
• one hydrogen atom
• two alkyl groups
What is the structure of a tertiary halogenoalkane?
A tertiary halogenoalkane has:
• no hydrogen atoms
• three alkyl groups
When hydrolysed, halogenoalkanes form what?
Alcohols
What is the general formula for the alcohol homologous series?
Cn H2n+1 OH
An alcohol is primary, secondary or tertiary depending on what?
Depending on which carbon atom the -OH group is bonded to
In which type of reaction do alcohols react to form halogenoalkanes?
Substitution
The reaction between alcohols and hydrochloride acid is fastest if the acid is primary, secondary or tertiary?
Tertiary
The reaction in which -OH can be swapped for bromine to make a bromoalkane requires what?
An acid catalyst
You can make iodoalkanes using what?
Red phosphorus and iodine
How can alcohols form alkenes?
Alcohols can be dehydrated by eliminating water in an elimination reaction
What is the simplest way to oxidise alcohols?
Burn them
What are the products when you burn any alcohol with oxygen?
Carbon dioxide and water
What can you use to mildly oxidise alcohols?
You can use oxidising agent acidified dichromate(VI).
What are primary alcohols oxidised to?
Aldehydes then to carboxylic acid
What are secondary alcohols oxidised to?
Secondary alcohols are oxidised to ketones
What are tertiary alcohols oxidised to?
Tertiary alcohols won’t be oxidised.
What three things do aldehydes and ketones have in common?
- They are both carbonyl compounds
- They both have the functional group C=O
- They both have the general formula: Cn H2n O
What is the structure of an aldehyde?
Aldehydes have a hydrogen and one alkyl group attached to the carbonyl carbon atom
What is the structure of a ketone?
Ketones have two alkyl groups attached to the carbonyl carbon atom
How can you test whether a compound is an aldehyde or a ketone?
You can use Bendict’s solution
What does Benedict’s solution consist of?
Blue solution of complexed copper (II) ions dissolved in sodium carbonate
What happens if Benedict’s solution is heated with an aldehyde?
Blue copper (II) ions are reduced to brick-red precipitate of copper (I) oxide
What happens if Benedict’s solution is heated with an a ketone?
Nothing happens as ketones can’t be oxidised easily
What is an electrophile?
A species attracted to negative charge/areas of high electron density
Explain why the major product of the reaction of propene with hydrogen bromide is 2-bromoprane, rather than 1-bromopropane.
- Secondary carbocation means that we have two alkyl groups feeding electron density to the carbocation
- Two alkyl groups means that the 2-bromopropane is more stable
Stats two necessary conditions used when cracking petroleum fractions.
- Aluminium oxide catalyst
* High temperature
