ib sl organic chemistry

alkanes undergo …

combustion, free-radical substitution

stages of free radical substitution (alkane + free radical - either bromine or chlorine) - only occur when?

initiation, propagation, termination - only occur in UV light

alkenes undergo …

hydrogenation, hydration, halogenation, addition polymerisation

hydrogenation of alkene formula and conditions

alkene + hydrogen → alkane

nickel catalyst, 180 degrees

C2H4 +H2 —> C2H6

hydration formula and conditions

alkene + steam h2o -→ alcohol

sulfuric/phosphoric acid catalyst

C2H4 +H2O —> C2H5OH

halogenation of alkenes

alkene + halogen → dihalogenoalkane

unsaturation test - color change from brown to colorless in bromine water - indicates presence of C=C bond

C2H4+H2O —> C2H4Br2

halogenation of alkenes

(with hydrogen halides like HCl)

alkene + hydrogen halide → halogenoalkanes

alcohols undergo …

combustion, oxidation (with suitable oxidising agent), esterification

oxidation of secondary alcohol →

ketones

heat under reflux

partial oxidation of primary alcohols →

aldehyde (CHO) (has lower b.p. - can burn quicker)

distilled to remove

complete oxidation of primary alcohols → … + conditions

carboxylic acid, heat under reflux, excess oxidising agent

combustion of alcohols formula

alcohol + O2 —> CO2 + H2O

oxidising agents for alcohols

potassium manganate (VII), acidified potassium dichromate

oxidation of tertiary alcohol -→

cannot occur (no hydrogen atoms)

esterification formula, conditions

carboxylic acid + alcohol → ester (COO) + water

concentrated sulfuric acid catalyst

heated under reflux

reversible reaction

halogenoalkanes undergo..

substitution nucleophilic reactions

strong metal hydroxide (OH- ion - nucleophile) attacks the carbon in the halogenoalkane, replacing the bonded halogen group with OH, leaving the halogen as a negative ion (heterolytic fission)

e.g. chloropropane + sodium hydroxide —> alcohol + Cl^-

nucleophile

electron-rich species

electrophile

electron-deficient species

what type of reaction does benzene undergo?

electrophilic substitution

maintains resonance in aromatic structure

examples: nitration, halogenation

benzene + nitric acid —>

nitrobenzene + water

NO2 replaces a H bond

conditions: sulfuric acid catalyst, 50 degree heat)

benzene + halogen —>

catalyst?

chlorobenzene + hydrogen halide (e.g. HCl)

a single Cl molecule replaces a H bond in ring

conditions: AlCl3 in dry ether

physical evidence for structure of benzene

• C-C bond lengths are intermediate between single and double bonds

• all bond angles are equal (considering regular hexagon structure)

chemical evidence for structure of benzene

• undergoes [electrophilic] substitution reactions more readily than addition reactions

• forms only 1 isomer for 1,2-disubstitution compounds

• more stable than theorized in kekule structure → enthalpy change of hydrogenation is less exothermic than predicted

what are the three factors affecting the volatility and boiling point of a compound?

• molar mass (b.p. increases with higher mm)

• branching (more branching = lower b.p. due to weaker IM forces + less surface contact between molecules)

• nature of functional group (polar = higher b.p. - e.g. OH or NH forms H bonds between molecules - strong IM bond)

what does the solubility of an organic compound depend on?

ability to form hydrogen bonds with water molecules

solubility decreases as length of C chain increases → increases the hydrophobic (lacking affinity to water) character of molecule as it becomes more non-polar

→ thus non-polar molecules have limited solubility - cannot form H bonds with water