Module 7 Flashcards
What is the order of priority of functional groups?
carboxyl - oic acid amide - amide / carbamoyl carbonyl (aldehyde) - al / formyl carbonyl (ketone) - one / oxo hydroxyl (alcohol) - ol / hydroxy amino (amine) - amine / amino alkene (ene) alkyne (yne) halo
Saturated
Single bonds between C atoms (alkanes)
Unsaturated
Double/triple bonds between C atoms (alkenes, alkynes)
The reaction of Alkenes with hydrogen
Hydrogenation
- Readily react in the presence of a Nickel catalyst to form an alkane
- Double bond ‘opens up’ to accept the H atoms via an addition reaction
- Results in the corresponding alkane forming (Ethene = Ethane)
The reaction of Alkenes with halogens
Halogenation
- no catalyst
- Double bond ‘opens up’ to accept the halogen atoms via an addition reaction
The reaction of Alkenes with hydrogen halides
- Hydrogen halides are molecules that contain 1 H and 1 halogen atom
- no catalyst
- addition reaction
The reaction of Alkenes with water
Hydration
- Requires heat and a catalyst (temp of about 300°C)
- Alkenes form corresponding alkanol (ethene = ethanol)
- Phosphoric acid or sulfuric acid used as catalyst
Markovnikov
The substituent (the halide in the hydrogen halide) adds to the more substituted carbon (the carbon with more H atoms already attached to it), the H will add to the other open bond on the carbon. (rich get richer).
Reactions of alkanes - substitution
- Because they are saturated they have to make room, for other atoms to substitute onto the molecule and replace existing atoms
- Requires UV light
What is polymerisation
It is a chemical reaction in which many identical small molecules called monomers, combine together to form 1 large molecule.
Occurs by the eq:
nH2C=CH2 → [―CH2CH2―]n
Explain why boiling point increases with each member in a homologous series.
- With each member in a homologous series, there is added molecular mass
- The strength of dispersion forces increases with molecular mass, as there are more electrons added, thus with each added member the strength of intermolecular forces increases
- This means more energy must be input to overcome these forces to turn these molecules into a gaseous phase
Explain how packing can impact the boiling point of an organic compound.
- Packing increases the boiling point of an organic compound
- Efficient packing resulting from a linear structure allows molecules to align more closely to one another, resulting in stronger intermolecular forces being experienced, thus raising boiling point
Identify the relationship between branching and boiling point
- Chain branching decreases boiling point
- Adding chains disrupts the shape of the molecule meaning multiple molecules cannot align closely with one another, thus decreasing IMFs experienced and boiling point.
Why do methane and ethane have higher melting points than propane?
- Methane and Ethane are smaller than propane allowing for a more ordered packing structure in the solid-state compared to propane
- This increases the overall IMF strength between the molecules and thus increases melting points
Why do hydrocarbons not dissolve in water?
- Hydrocarbons cannot dissolve in water since the adhesive forces they form with water are not able to overcome the cohesive forces within water.
- The cohesive forces within water is a strong network H- bonding between each water molecule
- The adhesive force formed between water and hydrocarbons are only relatively weak dispersion forces, hence this is not enough to overcome the cohesive force the hydrocarbon is not able to dissolve in water.
Water is less volatile than hexane. Account for this difference in terms of their intermolecular forces.
Water has stronger intermolecular forces compared to hexane, as it has H-bonding whereas hexane has weak dispersion forces. This means that hexanes intermolecular forces require less energy to overcome, allowing it to become a gas more easily. In contrast waters intermolecular forces require more energy to overcome, thus making it less volatile than hexane.
Would hexane dissolve into water? If not, what would we observe with the layers of solution formed? Justify your answer.
Hexane would not dissolve in water as the weak dispersion adhesive forces between the molecules would not be able to overcome the Waters strong h-bonding cohesive forces. Hexane would sit above water if the solutions were added together, as water is more dense than hexane due to its increased strength of intermolecular forces of h-bonding which reduce the distance between its molecules allowing it to have a higher measure of mass per unit of volume.
Which compound would have a higher viscosity, Hexane or water. Explain your prediction.
Water would have a higher viscosity as it’s molecules are more attracted to each other due to its strong intermolecular forces of h-bonding, this increased attraction also allows for increased resistance to fluid flow. Hexane has only weak dispersion forces between its molecules, thus decreasing it’s resistance to fluid flow.
Explain why amines have a lower bp than carboxylic acids despite also being able to form multiple hydrogen bonds.
- Amines have a lower bp as the hydrogen bonds formed are to N which is not as electronegative as O
- The H-bonds are thus weaker and can be overcome more easily
- Carboxylic acids are arranged in a dimer structure, which strengthens their H-bonds, further raising bp.
Explain why small amines, amides and carboxylic acids dissolve completely in water.
- All have highly polar functional groups
- The adhesive force of H-bonding between water and the polar functional groups on these compounds is strong enough to overcome the similarly strong H-bond cohesive forces and thus dissolution occurs.
Explain why longer amines, amides and carboxylic acids do not dissolve well in water.
- As chain increases, non-polar section increases
- This section cannot form adhesive forces with water, rather due to their increasing molecular mass, which provides them with additional electrons, they strengthen the cohesive dispersion forces of the organic solute, making adhesive forces too weak to overcome these cohesive forces, decreasing solubility.
Between Ethanoic acid and Dibromoethanoic acid, which acid will have a lower pH?
- Dibromoethanoic acid will have a lower pH
- This is due to the presence of two highly electronegative Br atoms, which, due to the inductive effect, draw electronegativity away from the O- in the hydroxyl group, weakening the O-H bond, allowing the H to be lost easier. (making it a stronger acid)
Condensation reaction
A reaction where two or more molecules combine to form a larger molecule with the simultaneous elimination of a small molecule, usually water.
Describe the reflux method.
Reflux is a technique that involves heating a reaction mixture in a vessel fitted with a cooling condenser so that the volatile reactants and products are returned to the reaction mixture without any loss.
Organic compound
A class of chemical compounds constituted primarily of hydrogen, oxygen and nitrogen covalently bonded onto a carbon chain backbone.
Explain why alkanes are known as saturated molecules but alkenes and alkynes are known as unsaturated.
- Alkanes are known as saturated molecules due to the presence of only carbon-carbon single bonds, meaning it is not possible to free any more bonds and attach another atom.
- Alkenes and alkynes are unsaturated due to the presence of carbon-carbon multi bonds, which are able to be turned into single bonds, freeing up bonds to attach another atom.
Structural isomers
Molecules that have the same molecular formula but different structural formulae. Their atoms are arranged differently resulting in completely different compounds. This also leads to different chemical and physical properties. (chain, position and functional group isomers are all types of structural isomers)
Chain isomers
Isomers which involve a rearrangement of the carbon atoms, causing changes in the length of the backbones by adding/removing/branching.
Position isomers
Molecules with the same carbon chain and same functional group, but with the functional group being in a different location.
Functional group isomers
Share the same molecular formula but have different functional groups. These isomers are in an entirely different homologous series resulting in significantly different chemical and physical properties.
Explain why boiling point increases with each member in a homologous series.
- With each member in a homologous series, there is added electrons due to molecular mass.
- Strength of dispersion forces increases with molecular mass, which adds electrons, thus with each added member the strength of intermolecular forces increases.
- This means more energy is required to overcome these forces to turn the molecules into a gaseous phase.
Explain why alkynes have a higher bp than alkanes which have a higher bp than alkenes.
- Boiling points are a measure of the thermal energy needed to overcome the IMF of a compound
- For all 3 homologous series, dispersion forces are the only type of IMF existent
- Thus, it would stand that alkanes have a higher bp than alkenes as it has a greater molecular mass, meaning more electrons, increasing the strength of the dispersion forces and thus the energy needed to overcome them
- However, alkynes have the highest bp’s because of the linear geometry of the triple bond allows it to overcome its MM deficiency
- This allows their molecules to benefit from the packing phenomenon as they can align more closely with one another, thus increasing the strength of their dispersion forces.
