Organic Chemistry - Explain

Explain valency

number of electrons an atom needs to gain, lose, or share to achieve a full outer shell

What is the valency of carbon

4

How many bonds can carbon form

4 covalent bonds

What is a covalent bond

chemical bond formed by the sharing of electrons between two non-metals

What types of covalent bond can there be

single, double, triple

General formula of alkanes

CnH2n+2

List alkanes

Methane, Ethane, Propane, Butane, Pentane, Hexane, Heptane, Octane, Nonane, Decane

General formula of alkenes

CnH2n

List alkenes

Ethene, Propene, Butene, Pentene, Hexene, Heptene, Octene, Nonene, Decene

General formula of alcohols

CnH2n+1OH

List alcohols

Methanol, Ethanol, Propanol, Butanol, Pentanol, Hexanol, Heptanol, Octanol, Nonal, Decanol

General formula of carboxylic acids

CnH2n+1COOH

List carboxylic acids

Methanoic acids, Ethanoic acids, Propanoic acids, Butanoic acids, Pentanoic acids, Hexanoic acids, Heptanoic acids, Octanoic acids, Nonanoic acids, Decanoic acids

Importance of functional groups

determine the chemical properties of a molecule

Explain the structure of alkanes

made up of carbon and hydrogen atoms, each carbon atom forms 4 single covalent bonds

Explain the general formula of haloalkanes

based on alkane, but with halogen(s) replacing H

Explain the structure of haloalkanes

similar to alkanes but include one or more halogen atoms bonded to the carbon atom

Explain naming haloalkanes

Fluoro, chloro, bromo, iodo

what happens if there is more than one halogen

list them alphabetically

Why do structural isomers matter

Structure affects function. Isomers often have different physical (bp) and chemical properties

Explain melting point

The temperature at which a substance changes from solid to liquid

Explain boiling point

The temperature at which a substance changes from liquid to gas

Explain the trend in mp and bp for alkanes

As the carbon chain length increases, the melting and boiling points of alkanes increase. This is because a longer carbon chain means a larger molecular mass and more electrons. As a result, the strength of the intermolecular forces increases. Stronger intermolecular forces mean that more energy is required to overcome these forces, leading to higher melting and boiling points.

Explain the overall mp/bp of alkanes (why)

Alkanes have low mp/bp because they are non-polar molecules, so the intermolecular forces between them are weak. These forces are relatively easy to overcome, so less energy (heat) is needed to melt or boil them

Explain the trend in solubility for alkanes/haloalkanes (polar solvents)

As the carbon chain length increases, the solubility of alkanes/haloalkanes decreases. This is because as more carbon atoms are added to the main carbon chain, the polar functional groups takes up a smaller portion of the molecule.

Explain the trend in solubility for alkanes/haloalkanes (non-polar solvents)

As the carbon chain length increases, the solubility of alkanes and haloalkanes in non-polar solvents increases. This is because alkanes are non-polar, this follows the “Like dissolves in like”

Define Geometric Isomers

molecules with the same molecular formula and the same order of atoms ), but they differ in the spatial arrangement of groups around a carbon–carbon double bond. This is due to restricted rotation around the double bond.

Define Cis Isomers

the same groups are on the same side of the double bond

Define Trans Isomers

the same groups are on opposite sides of the double bond

Define Structural Isomerisation

molecules have the same molecular formula but different structural formulas.

Explain why unsaturated hydrocarbons can exist as isomers

Unsaturated hydrocarbons can exist as isomers due to geometric isomerism, which arises from the restricted rotation around the carbon-carbon double bond. Double bonds consist of a sigma bond and a pi bond: the pi bond prevents free rotation, locking the spatial arrangement of the atoms attached to the carbon-carbon double bond. Because of this restricted rotation, the groups can be attached on the same side of the double bond or on the opposite side.

What type of reaction + Name of reaction: Alkene > Alkane

Hydrogenation: Addition Reaction

What reagent is used: Alkene > Alkane

(mention a catalyst if required)

H2 + Pt/Ni Catalyst

What type of reaction + Name of Reaction: Alkene > Haloalkane

Hydrohalogenation + Addition Reaction

What reagent is used: Alkene > Haloalkane

(mention catalyst if necessary)

HCl

HBr

What type of reaction is this + Name of Reaction: Alkene > DiHaloalkane

Halogenation + Addition Reaction

What reagent is used: Alkene > DiHaloalkane

(name catalyst if necessary)

Cl2

Br2

What type of reaction is this + Name of Reaction: Alkene > Alcohol

Hydration + Addition Reaction

What reagent is used: Alkene > Alcohol

(mention catalyst if necessary)

H20

(H2SO4)

What do all addition reactions have as their product

alkenes

Define “Addition” Reactions

chemical reactions in which atoms or groups of atoms are added across a carbon–carbon double bond in an unsaturated molecule . The pi bond in the double bond breaks, allowing new atoms to bond to each of the carbon atoms. This results in the formation of a saturated compound.

Where do the new atoms or functional groups come from in addition reactions

the particular reagent added

Define elimination reactions

chemical reactions in which atoms or groups of atoms are removed (eliminated) from a molecule, resulting in the formation of a carbon–carbon double bond.

What type of reaction is this + Name of reaction: Alcohol > Alkene

Dehydration + Elimination Reaction

What reagent is used: Alcohol > Alkene

(mention catalyst if necesary)

no reagent is used - only H2SO4

What type of reaction is this + Name of reaction: Haloalkane > Alkene

Dehydrohalogenation + Elimination Reaction

What reagent is used: Haloalkane > Alkene

(mention catalyst if necessary)

KOH (alc)

What do all elimination reactions produce

alkenes

How to identify saturated hydrocarbons from unsaturated molecules

Bromine water - unsaturated molecule, the bromine water decolourises

saturated molecule, no colour change is observed

Explain Markovnikov’s Rule + when to use

the hydrogen atom is added to the carbon with the highest number of hydrogen atoms already attached. Apply it to addition reactions of assymetrical alkenes

Explain Polyethylene

plastic bags, containers. Because it is Flexible, chemically resistant, and waterproof

Explain polypropylene

containers, medical equipment. Because it is chemically resistant, withstand high temp, and lightweight

Explain Polyvinyl Chloride

pipes, window frames. Because it is chemically resistant, rigid, and electrical insulator

Explain Nylon

Clothing and rope. Because it is lustrous, strong, and chemically resistant

Explain Polystyrene

packaging foam and disposable cutlery. Because it is lightweight, low mp, and good insulator

What are cracking reactions

chemical reactions in which large hydrocarbons are broken down into smaller, more useful molecules, including short-chain alkanes and alkenes

State a purpose of cracking reactions (fuel)

increase the supply of useful hydrocarbons such as petrol, which contains short-chain alkanes

State a purpose of cracking reactions

produce alkenes which are more reactive than alkanes and are essential as monomers in polymer production

State an example of cracking reaction (decane)

C10H22 > C8H18 + C2H4

Octane is used in petrol

Ethene is used to make plastics

State the trend of solubility for alcohols

Alcohols with less than 5 carbon atoms are soluble in water. However, as the carbon chain length increases, solubility decreases

Explain the trend of solubility for alcohols

The –OH group in alcohols is polar and can form hydrogen bonds with water molecules.
In small alcohols, the polar –OH group dominates the molecule’s behavior, so they dissolve well in water.
As the chain gets longer, the non-polar hydrocarbon portion increases, making the molecule more hydrophobic and less soluble in water.

State the trend in mp/bp for alcohols

As the carbon chain length increases, melting point and boiling point increase (alcohols)

Explain the trend in mp/bp for alcohols

As the carbon chain length increases, the molecular mass increases. There are stronger intermolecular forces and so more energy is required to overcome these forces, therefore boiling/melting points rise (alcohols)

Why do alcohols have a higher mp/bp than alkanes of similar mass

Alcohols can form hydrogen bonds between their molecules due to the –OH group, which leads to higher melting and boiling points than alkanes of similar mass.

What is a diol

a compound with 2 hydroxyl groups

What reagent is used to form diols from alkenes

MnO4-/H+

What type of reaction occurs when an alkene forms a diol?

An oxidation/addition reaction where OH groups are added across the C=C double bond

What happens to the double bond during diol formation?

The double bond breaks, and an OH group adds to each carbon of the former double bond.

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What type of reaction forms an alcohol from a haloalkane?

A substitution reaction, where the halogen is replaced by an –OH group.

What reagent is used to convert a haloalkane into an alcohol?

Aqueous potassium hydroxide (KOH(aq))

What happens to the halogen in a substitution reaction with KOH(aq)?

It is replaced by an –OH group, and leaves as a halide ion (e.g., Cl⁻, Br⁻) combining with K-

What type of reaction occurs between an alcohol and a hydrogen halide?

A substitution reaction, where the –OH group is replaced by a halogen.

What are the products of the reaction between an alcohol and a hydrogen halide?

A haloalkane and water.

What is the product when a primary alcohol is fully oxidised?

A carboxylic acid.

Where does the hydroxyl group have to be on the carbon atom to be oxidised to a carboxylic acid

on the 1st carbon

What oxidising agents are commonly used to oxidise primary alcohols?

MnO4-/H+

Cr2O72-/H+

What is the intermediate product formed when a primary alcohol is partially oxidised?

An aldehyde.

What colour change occurs when acidified potassium dichromate oxidises a primary alcohol?

Orange to green.

What colour changes occur when acidified permanganate oxidises a primary alcohol

Purple to colourless

What type of reaction occurs when alcohols react with PCl₃, PCl₅, or SOCl₂?

A substitution reaction where the –OH group is replaced by –Cl.

Write the general reaction with PCl3

3R–OH + PCl3 ​→3R–Cl + H3​PO3​

What does the alcohol and PCl3 reaction require

heating

Write the general equation for the reaction with alcohol and PCl5

R–OH + PCl5 ​→ R–Cl + POCl3​ + HCl

What temperature does the alcohol reaction with PCl5 occur at

room temperature

Write the general equation for alcohol and SOCl2

R–OH + SOCl2​ → R–Cl + SO2 ​+HCl

What is added to the alcohol reaction with SOCl2

a base like pyridine to neutralise the HCI formed

What type of reaction removes hydroxyl groups from alcohols to form alkenes

An elimination reaction (also called dehydration).

What two parts are removed from the alcohol molecule during elimination?

A hydrogen atom (H) and a hydroxyl group (–OH).

What catalyst is commonly used for the dehydration of alcohols?

Concentrated sulfuric acid (H₂SO₄)

What is the product formed when ethanol undergoes dehydration?

Ethene and water (H₂O).

Which rule predicts the major alkene product in alcohol dehydration?

Anti-Markovnikov’s Rule; the Carbon atom that has the least amount of hydrogens attached is the one that loses the hydrogen atom

What are amines

compounds that contain the amino functional group (-NH2)

What type of reaction produces amines from haloalkanes?

substitution.

What reacts with haloalkanes to form amines?

Ammonia (NH3(alc))

What is the general equation for amine formation from a haloalkane?

R–X + NH 3 ​→ R–NH2 ​+ HX

State the trend in solubility for amines

Amines with up to 5 carbons are soluble in water. However, as the carbon chain length increases, solubility decreases

Explain the trend in solubility for amines

the –NH₂ group can form hydrogen bonds with water molecules. However, as the carbon chain length increases, the hydrophobic carbon chain reduces solubility in water. Therefore, longer-chain amines are less soluble due to the dominant non-polar hydrocarbon part.

State the trend in mp/bp for amines

As the carbon chain length increases, the melting and boiling points of primary amines increase.

Explain the trend in mp/bp for amines

As the carbon chain length increases, the molecular mass increases. There are stronger IMF forces. More energy is required to overcome these forces, so mp/bp increases

Why are carboxylic acids acidic?

Carboxylic acids contain the carboxyl functional group (–COOH). They can donate a proton (H⁺) from the hydroxyl (–OH) part of this group, making them acids.

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