Chemistry Brainscape Organic Flashcards
What is the functional group of an alkene?
C=C
What is the functional group of an alcohol?
O-H
What is the functional group of an alkane?
C-H
What is the functional group of an aldehyde?
O=C-H
What is the functional group of a carboxylic acid?
O=C-OH
What is the functional group of an ester?
O=C-O
What is the functional group of a halogenoalkane?
X-C-H
What is the functional group of a ketone?
C=O
What is the functional group of a nitrile?
carbon triple bonded to nitrogen
What is the functional group of an amine?
H-N-H
Is an alkene saturated or unsaturated?
unsaturated
What is the double bond consisted of?
A sigma and a pi bond
What is a sigma bond?
A single covalent bond formed by the overlap of S-S, S-P, or P-P orbitals. This forms a region of electron density concentrated between two nuclei.
What is a pi bond?
A double covalent bond formed by the sideways overlap between two p orbitals. This forms two regions of electron density above and below the plane of a molecule.
Why is there restriction around the double bond?
The regions of high electron density both between, above and below the molecules prevents rotation.
Why does E/Z isomerism (stereoisomerism) arise?
Due to the restriction of rotation around the double bond, and the presence of different groups attached to the carbons at the end of the bond.
How does increasing the number of carbon atoms in an alkene affect its properties?
The more carbon atoms, the more intermolecular forces there are, increasing the overall strength of bonding (cumulative significance). This increases the melting and boiling points.
Are alkenes soluble in water?
No, only in organic solvents
Why are alkenes insoluble in water?
They are not polar, so are unable to form hydrogen bonds with water
Why are alkenes non-polar?
The C-C and C-H bonds have a very small electronegativity difference, therefore they are not polar bonds.
What does solubility mean?
The energy taken to break bonds in both molecules has to be equal to the energy taken to form new bonds between them
Why are non-polar compounds insoluble in water?
The only forces in non-polar compounds are London forces while in water there are hydrogen bonds. The energy taken to break and form London forces is far less than the energy taken to break and form hydrogen bonds.
What are the differences in combustion of alkenes and alkanes?
Alkenes burn with a smokier/sootier flame, due to the higher carbon percentage
Describe the reaction of addition to hydrogen to alkenes
The alkene’s double bond is removed, producing the respective alkane
What are the conditions and reagents for addition of hydrogen to alkenes?
either 1) room temperature with a platinum/palladium catalyst or 2) 150C with a nickel catalyst
Why is a solid metal catalyst used for catalytic hydrogenation?
better because the catalyst is easier to extract and has no changes to it, also better for adsorption
What is the addition reaction of hydrogen to alkenes also known as?
Catalytic hydrogenation
Describe the reaction of addition to halogens to alkenes
The double bond is removed, and the two halogen atoms added to the chain, producing a dihalogenoalkane (e.g. dichloroalkane)
What is the mechanism for addition of halogens to alkenes?
Electrophilic addition
What is produced when adding steam to alkenes?
An alcohol
What is the condition for addition of steam to alkenes?
Acid catalyst (provides adsorption)
What is the mechanism for addition of hydrogen halides to alkenes?
Electrophilic addition
What are the tests between saturated and unsaturated hydrocarbons?
Bromine water - turns colourless from brown-yellow Potassium manganate (VII) turns from purple to colourless
Describe the process of fractional distillation
1) mixture is heated then passed into the fractioning column
2) the separation of fractions depends on their boiling point
3) substances with low boiling points will evaporate to gases and pass out of the top
4) substances with high boiling points either condense at the middle or stay at the bottom as solids
What is the trend up the fractioning column?
higher flammability, lower boiling point, lower viscosity
How are fuels obtained from crude oil?
fractional distillation -> cracking -> reforming
What is fractional distillation?
separates similar size hydrocarbons from the mixture of hydrocarbons because they are used as fuels
What is cracking?
the conversion of large hydrocarbons into smaller ones by breakage of C-C bonds
What is reforming?
the conversion of straight chain alkanes into branched/cyclic alkanes and aromatic hydrocarbons
Why is reforming used?
the new products burn more cleanly and efficiently due to their higher octane number making them more stable
Why are alkanes good fuels?
they burn readily in the presence of oxygen, and the combustion is highly exothermic
Describe the reaction behind bromine water turning colourless in the presence of an alkene
When bromine water is shaken with ethene (example), electrophilic addition occurs.
Because there are both water molecules and bromine ions present, they can both act as electrophiles.
What are the two products of the electrophilic addition of bromine water and ethene?
1,2- dibromoethane (halogenoalkane) and 2-bromoethanol (alcohol). More 2-bromoethanol is produced more because there are more water molecules.
Why are halogenoalkanes polar?
There is a significant electronegativity between Carbon and its Halogen atom, therefore producing a permanent dipole.
Compare the boiling points of halogenoalkanes and their parent alkanes and explain the trend.
Halogenoalkanes have higher boiling points. This is because alkanes have only London forces present, whereas H-Alkanes have permanent dipole-dipole forces (stronger).
Can halogenoalkanes mix with water?
No, because the dipole-dipole forces are much weaker than hydrogen bonds (solubility rule)
What is the solubility rule?
In order for two substances to fully dissolve, the energy taken to break the bonds in both substances must be equal to the energy released in making the bonds between them.
This is why water does not mix with alkanes/halogenoalkanes. Hydrogen bonds require a lot more energy to break and make than London forces.
Describe the process needed for alkene -> halogenoalkane
- addition of a hydrogen halide
- room temperature
Describe the process needed for alkane -> halogenoalkane.
- heating or UV light
- chlorine or bromine
- leading to free radical substitution
Describe the process needed for alcohol -> halogenoalkane.
- addition of phosphorus or hydrogen halides
Draw the mechanism for the free radical substitution of alkanes and halogens.
