IB Chemistry HL topics 1-21 + option B

2016-2024 syllabus

Alkane combustion reaction

Complete : results in CO2 forming

Incomplete results in CO or C forming

What causes free radical substitution of alkanes

UV radiation

Define homolytic fission

Homolytic fission is a type of chemical bond cleavage in which a covalent bond breaks, and each atom retains one of the shared electrons. This results in the formation of two free radicals, each with an unpaired electron.

Define free radical

A free radical is an atom, molecule, or ion that contains an unpaired electron. It is highly reactive as they are unstable.

Free radical substitution steps

Initiation: photochemical homolytic fission of the bond between two halogen atoms due to incident UV radiation.

Propogation: Free radical + Molecule

Termination: Free radical + Free radical

Why are alkenes reactive

• Pi bond is weaker than sigma bond

• double bond is electron dense

Alkene addition reaction types

• Halogenation

• Hydrohalogenation

• Hydrogenation

• Hydration

• Polymerisation

Halogenation reaction + condition

no condition

Hydrohalogenation reaction + condition

Heat

Hydrogenation reaction + condition

150°C + Ni

Hydration reaction + condition

Concentrated sulfuric acid + heat

Polymerisation reaction + condition

High temp + pressure + catalyst

Combustion of alcohols…

completely and selectively oxidises the carbon atom attached to the -OH group

Alcohol oxidation catalyst and colour change

KMnO4 / H+ (aq) + heat

Purple → Clear

Primary alcohol oxidation reaction

Primary Alcohol → Aldehyde → Carboxylic acid

note: You don’t need to know the intermediate step!

Secondary alcohol oxidation

Alcohol → Ketone

Tertiary alcohol oxidation

resistant to oxidation

Esterification reaction + catalysts

Alcohols react with carboxylic acid to form esters in a condensation reaction.

Condition: Heat + conc. H2SO4

conditions for sigma bonds

• two S-orbitals

• one S-orbital and P-orbitals

• Two P- orbitals in the same axis

Pi bonds

• not as strong as sigma bonds

• overlap of Py and Pz orbitals lengthways

• occurs when two atoms come close to each other

• double / triple bonds are electron dense

Define stereoisomers

A compound with the same structural formula, but arranged differently in space

Define cis-trans isomer

When two compounds have the same structural formula, but groups are arranged differently around a double bond or ring

Why are cis-trans isomers configurational and not conformational?

The double bond or ring restricts the rotation

Which cis-trans isomer has a higher boiling point and why?

Cis-ethene, because of the assymetrical distribution of charge forming dipoles, meaning it has both LDF and dipole-dipole intermolecular forces.

Trans-ethene on the other hand is symmetrical in distribution of charge and hence is a non-polar molecule, and only has weaker LDF.

How do you determine priority in naming cis-trans isomers

higher molecular mass = higher priority

E/Z naming system

Cis = Z

Trans = E

What is needed to exhibit optical isomerism

There must be four different groups attached to a Carbon ‘centre’

What type of reaction is esterification

Condensation

Define Chiral

non-superimposable mirror image (assymetric)

Define enantiomer

one of a pair of optical isomers, which are mirror images of each other

Define racemic mixture

an equimolar mixture of two enantiomers (mirror pair) of chiral compounds

Plane polarised light

light that vibrates in one plane only, radiation can be polarised at different rotations depending on which enantiomer it passed through in the pair

Define optically active

optically active means the compound is capable of polarising the plane of light

Physical and chemical properties of enantiomers

Physical: identical except rotation of plane polarisation

Chemical: Identical for reactions with compounds which are not optically active. Enantiomers may react differently with optically active compounds.

Diastereomers

• cis-trans whilst exhibiting optical isomerism

• not mirror images

• can have multiple chiral centres

Conformational isomers

• rapidly interconverts between staggered and eclipsed conformation at room temperature due to low energy difference

• converts via rotation about the single bond

Types of nucleophilic substitution and conditions

Primary halogenoalkanes → Sn2 reaction

Tertiary halogenoalkanes → Sn1

Secondary halogenoalkanes → Sn1 + Sn2 mix

Draw out an Sn2 reaction

if its chiral it inverts like an umbrella

What does bimolecular and unimolecular reaction mean for the rate

Bimolecular - two species are involved in the rate determining step.

Unimolecular - one species involved

Sn2 reactions are bimolecular as the nucleophile and the halogen move in the same step. So the concentration of both species matters - Rate = k[halogenoalkane][nucleophile]

Sn1 is not because only the concentration of the initial species matters. Rate = k[halogenoalkane]

Define steric effect

how readily the compounds can be substituted in regards to ‘space’

energy level diagrams of Sn1 and Sn2 reactions

Define heterolytic fission

Covalent bond breaks, electron pair goes to the same side

Draw out an Sn1 reaction

REFER TO HETEROLYTIC FISSION WHEN EXPLAINING

What affects the rate of nucleophilic substitution

• structure

• halogen

• nucleophile

• solvent

How does struture affect rate of nucleophilic substitution

Sn2: steric effects (space)

Sn1: positive inductive effects stabilises carbocation

How does halogen affect rate of nucleophilic substitution

R-I > R-Br > R-Cl > R-F

higher atomic mass = faster rate of reaction

how does nucleophile affect rate of nucleophilic substitution

Sn2: more negative = faster reaction. e.g OH- > H2O

Sn1: no effect because it is not in the Rate Determining Step (RDS)

What is a polar protic and polar aprotic solvent

Protic - can participate in H-bonding (e.g. water)

Aprotic - can’t participate in H-bonging (e.g. Propanone)

How does solvent affect rate of nucleophilic substitution

• Sn1 favoured by protic polar - as it is a good ionizing solvent and thus stabilises the carbocation

• Sn2 favoured by aprotic polar - as it is not good at solvating the nucleophile and thus it’s easier to attack the nucleus

Why do alkenes undergo electrophilic addition

• 120 degree bond angle

• double bond is electron dense, therefore attractive to electrophiles

Draw the ethene + bromine mechanism and explain it

• bromine is polarised by electron rich double bond

• Br2 splits forming Br+ and Br-

• Br+ (electrophile) attacks double bond, attaching to it (slow/RDS)

• unstable carbocation reacts with Br- (fast)

What is the bromine test used for

determining whether a hydrocarbon is saturated (single bonds) or unsaturated

Draw out the ethene + hydrogen bromide reaction mechanism

similar to ethene + bromine mechanism

Draw out assymetric electrophilic addition and explain why it occurs

When the double bond is not in the middle, 2 different carbocation intermediates can be formed.

Define positive inductive effects

• alkyl group (alkane minus a hydrogen) can push electron density away from themselves

• greater positive inductive effects mean the carbocation is more stable, hence mechanism (b) is preffered over (a)

Markovnikov’s rule

The hydrogen will attach to the carbon that is already bonded to the greater number of hydrogens

why does benzene undergo electrophilic substitution

• simplest aromatic hydrocarbon compound (or arene)

• Carbon to carbon bonds have a bond order of 1.5

• delocalised structure of pi bonds around its ring

• highly unsaturated, however doesnt behave like other alkanes

• highly stable, more likely to undergo substitution (so as to not lose stability from delocalised pi electrons)

• ring is electron dense, so it attracts electrophiles

• delocalised electrons seek electrophiles, forming a new bond, losing a H → electrophilic substitution

Draw out and explain the Nitration of benzene mechanism

catalyst: Conc. H2SO4 + heat

• electron pair of benzene attracted to Nitronium as it is a strong electrophile

• Disrupts the delocalised electron ring

• NO2+ and hydrogen temporarily attached to unstable carbocation intermediate

• electrons from C-H bond are used to reform the arene ring, losing the H+ and forming nitrobenzene (appears as yellow oil)

• H+ released reacts with HSO4- to form H2SO4 again

Reduction vs oxidation in organic chem

Most reduced: more hydrogens

Most oxidised: more oxygens

Draw out Reduction reactions of carbonyl compounds

Primary and secondary alcohol oxidation can be reversed by adding reducing agents

all reactions done in acidic conditions

What are the reducing agents for carbonyl compounds

1. NaBH4 (Sodium borohydride) in aqeous or alcoholic solution, or

2. LiAlH4 (Lithium aluminium hydride) in anhydrous conditions, e.g. dry ether followed by aqeous acid.

Draw and explain the reduction of nitrobenzene reaction mech-anism

C6H5NO2 (nitrobenzene) can be reduced to C6H5NH2 (phenylamine) in a 2 step process.

1. C6H5NO2 reacts with a mixture of Sn/Conc. HCL under heat. Acidic conditions protonate the product, phenylammonium ions (C6H5NH3+)

2. C6H5NH3+ is reacted with NaOH to remove the H+ and form C6H5NH2

Define synthetic routes

series of discrete steps involved in the production of organic compounds

Define retro-synthesis

Working backwards from a desired target molecule

target molecule → precursor → starting materials

What is an electrophile

An electrophile is an electron-deficient species that can accept electron pairs from a nucleophile. Electrophiles are lewis acids.

Explain why a hydroxide is a better nucleophile than water

A hydroxide ion is a better nucleophile than water because it has a negative charge, making it more electron-rich and reactive in nucleophilic reactions. Water is less nucleophilic due to its neutral charge and lower reactivity.

NaOH (aq) + R-X (nucleophilic substitution)

Rate of Sn1 > Sn2

Curly arrows and fishhooks

Heterolytic fission: Curly arrows

Homolytic fission: fish hook

emphasise this on all mechanism diagrams

list halogenoalkanes, alkanes, and alkenes in order of reactivity

Alkenes > Halogenoalkanes > Alkanes

explain distillation and reflux and why its used for alcohols

• Distillation: Separates components based on boiling points. Aldehyde (lower boiling point) vaporizes first.

• Reflux: Prevents loss of volatile components by condensing vapors back into the reaction mixture.

NaBH4 (sodium borhydride)

catalyst for reducing aldehydes and ketones to primary/secondary alcohols

LiAlH4 (lithium aluminium hydride)

catalyst for reducing carboxylic acids

stronger than NaBH4, cannot be stopped at aldehyde stage, goes straight primary alcohol hole

Anabolism

reaction of synthesis (monomer → polymer) Requires energy

Metabolic pathways

a series of chemical reactions in a cell

Catabolism

Reaction of breakdown (polymer → monomer) Releases energy

Where do most metabolic reations takes place?

highly controlled aqueous environments (since 90% of a cell’s cytoplasm is water)

Factors affecting function and ability to react successfully in metabolic processes

• Shape

• Structure

• Chirality (HL)

Factors that must be maintained to ensure optimal cell function in metabolic process

• PH

• Temperature

• Concentration of components within the cell’s cytoplasm

Photosynthesis

The synthesis of energy-rich molecules from carbon dioxide and water using light energy. (endothermic)

Respiration

A complex set of metabolic process providing energy for cells. (exothermic)

Aerobic vs Anaerobic

Aerobic: with oxygen

Anaerobic: in the absence of oxygen

write the equilibrium equation for photosynthesis and cellular respiration

Condensation reaction

• produces water from H+ and OH-

• Heat and acidic environment is often required

• Anabolic

Hydrolysis

• water breaking → H2O splits to H+ and OH-

• Heat + Acid catalyst/enzymes required

• Enzymes ensure it doesn’t reverse

• Catabolic

Proteins

biopolymers of 2-amino acids, joined by amide links / peptide bonds

Polypeptide chains

• more than 3 amino acids joined by peptide bonds

• formation occurs in condensation reactions, reversed in hydrolysis

Isoelectric point

the pH at which a molecule carries no net electrical charge. It is the pH at which a molecule is electrically neutral.

What determines Isoelectric point

R groups. Acidic R groups favour acidic isoelectric point, vice versa.

Zwitterion

A molecule with both positive and negative charges, making it electrically neutral. It forms when an amino acid is at its isoelectric point.

Primary protein structure

• sequence of a chain of amino acids

• bond: contains peptide bonds

• example: polypeptide chains

Secondary protein structure

• amino acid folds into a repeating pattern due to H-bonds

• bond: Hydrogen bonds between COOH and NH2

• example: alpha helix and beta pleated sheets

Tertiary protein structure

• Three dimensional folding pattern of a protein due to side chain interactions

• Bonds: between R-Groups

  • Hydrogen bonds: helps stabilise protein molecule

  • Disulfide bonds: strong covalent formed by oxidation of -SH groups in cystein side-chains

  • LDF: when two molecules are close to eachother they can appear

  • Ionic bonds: Weak electrostatic interactions

• Example: myoblin or enzymes

Quarternary protein structures

• Proteins consisting of multiple polypeptide chains

• Bond: between R-Groups

• Example: Haemoglobin

What determines the role of a protein

3D shape determines its role in structural components (e.g. inside cells, tissues, organs, etc) or in metabolic processes

Globular proteins

• spherical in shape

• soluble in water due to polar R groups being on the outside, whilst non-polar R groups are on the inside

• act as chemical messengers (hormones), catalysts (enzymes), and tranpsport molecules.

• high temperatures denature the protein by weaking it’s IMF

Fibrous proteins / scleroproteins

• Long linear bundles of polypeptide chains, held together by covalent bonds, SS bridge, or H-Bond.

• insoluble in water due to exposed R groups being a mix of polar / non polar

• Form the basis of structural elements (cells, tissues, etc.) in organisms

• not as sensitive to high temperatures, as covalent bonds > IMF

Enzymes

• “biological catalysts”

• IB: most enzymes are proteins that act as catalysts by binding specifically to a substrate at the active site

• usually aqueous as they are homogenous catalysts (same state as other reactants)

Lock and key model

• An enzyme has a cleft in its surface, called the active site. The substrate molecule has a complimentary shape

• An enzyme-substrate complex is temporarily formed. The R groups of the amino acids in the active site interact with the substrate.

• The substrate is broken apart and the two product molecules leave the active site without damaging the enzyme molecule.

Induced fit model

• An enzyme has a cleft in its surface, called the active site. The substrate molecule does not have a complimentary shape

• The enzyme changes shape slightly as substrate binds

• enzyme-substrate complex is temporarily formed. The R groups of the amino acids in the active site interact with the substrate.

• The substrate is broken apart and the two product molecules leave the active site without damaging the enzyme molecule.

What factors affect enzymatic activity

• Concentration

• Temperature

• pH

• Heavy metal ions