Core organic chemistry

nomenclature

the IUPAC rules for naming compounds

name stem

the first part of the name, based on the number of carbon atoms

name ending

the functional group gives the ending to the name

complex molecules

• the molecule is named after the longest possible carbon chain containing the functional group

• the carbons are numbered to give the functional group the lowest number possible

• side chains are written as prefixes to the name

rings

for molecules that contain rings, add ‘cyclo-’ at the start of the name

empirical formulae

the simplest whole number ratio of atoms in a molecule

molecular formulae

gives the number of each type of atom in a molecule

structural formulae

written one-line formula showing which groups are connected to which

displayed formulae

diagram which shows every bond in a molecule

skeletal formulae

simplified displayed formula, hydrogen atoms aren’t shown and the carbon atoms are at the corners of any line

homologous series

set of compounds with the same functional group, members have very similar properties due to same functional group

general formula

gives the molecular formula for each compound in the homologous series

functional group

group of atoms that characterise the chemistry of a molecule, causing specific reactions to happen with certain reagents

alkyl group

saturated hydrocarbon chain attached to a molecule, ‘R’ can be used to represent it

aliphatic

contains carbon chains that do not involve a benzene ring

alicyclic

aliphatic compounds that have non-aromatic rings but no side chains

aromatic

compounds that contain at least benzene rings, making these compounds smell

saturated compounds

contains only single carbon carbon bonds

unsaturated compounds

contains at least one double carbon carbon bond or an aromatic ring

structural isomers

molecules which have the same molecular formula but a different arrangement in space

types of structural isomers

• chain isomers - molecules that have the same molecular formula but one is linear and one is branched

• position isomers - molecules that have the same molecular formula but have their functional group in different places

• functional group isomers - isomers that have had their structures changed so that they have different functional groups

bond fission

the breaking of covalent bonds

heterolytic fission

where the bond is broken unevenly, one atom retains bond bonding electrons and the other leaves with none

homolytic fission

where the bond is broken evenly, each atoms retains one of the bonding electrons, leading to the formation of two radicals

radicals

atoms or compounds that contain an unpaired electron, extremely unstable and highly reactive

reaction mechanisms

shows the formation of new bonds in the sequence they are created

curly arrows

used to show the movement of a pair of electrons

double pointed head curly arrow

shows the breaking of a bond

alkanes

• saturated hydrocarbons

• general formula - C_nH_2n+2

• every carbon atom in an alkane is bonded to 4 other atoms via single covalent bonds, forming a tetrahedral arrangement of bonds (109.5^o bond angle), due to electron pair repulsion theory

electron pair repulsion theory

regions of negative charge about an atom will repel to be as far apart from each other as is possible in a sphere

sigma bonds

C-H and C-C bonds found in alkanes are known as sigma bonds, electron orbitals overlap directly between the two atomic nuclei, allowing free rotation of the atoms at either end

boiling points of alkanes

• straight-chain alkanes, the boiling point increases with chain length as there are more london forces acted upon the molecule

• branching reduces the boiling point as it reduces the extent to which 2 molecules can align and form london forces

reactivity of alkanes

generally unreactive as there is a high bond enthalpy, meaning a lot of energy is needed to break the bonds and it has sigma bonds, meaning there is a lack of bond polarity

complete combustion of alkanes

• gives a blue flame

• produces only CO₂ and water

incomplete combustion of alkanes

• orange smoky flame, due to carbon glowing red hot

• produces CO₂, water and carbon, hydrocarbons and CO

• more likely with longer chain alkanes as they need more oxygen to combust completely

chlorination

conditions: UV light

products:

• with excess methane - chloromethane

• with excess chlorine - tetrachloromethane

three stages:

• initiation

• propagation

• termination

initiation

generates free radicals

propagation

involves a free radical and generates a new free radical

termination

involves two free radicals forming a covalent bond

limitations of radical substitutions in alkanes

• radicals are extremely reactive so further substitution can happen

• no control over the point on the carbon chain at which substitution happens

• you can also produce products that aren’t the desired haloalkane such as longer alkane chains

alkenes

unsaturated hydrocarbons, high electron density between the carbon atoms due to double bond

general formula - C_nH_2n

C=C is made up of one sigma bond and one pi bond, which involves electrons in the p-orbital existing above and below the plane of the bond, meaning no overlapping and causes the bond unable to rotate

carbon atoms at either end of the double bond each have 3 regions of negative charge around them, the electrons in these bonding regions repel each other to be equally around them, resulting in a 120^o bond angle

stereoisomers

molecules that have the same molecular formula, same functional groups and same functional group positions but different arrangements of atoms in space

E-alkene

has larger groups on opposite sides

Z-alkene

has larger groups on the same side

Cahn-Ingold prelog rules

numbering the 4 directly connecting atoms in order of their atomic mass number, ordering their priority

reactions of alkenes

alkenes are nucleophiles because of the high electron density between the carbon atoms, reacts with hydrogen bromide, sulfuric acid and bromine under electrophilic addition mechanisms

electrophilic addition mechanisms

for reactions that have an electrophile added

uses of electrophilic addition

with bromine

• used as a test for alkenes, bromine water is orange and would be decolourised in the presence of an alkene

with sulfuric acid

• producing alcohols using conc sulfuric acid and water

• alkene reacts with sulfuric acid forming an alkyl (hydrogensulfate) which is then diluted with water and distilled to make an alcohol

• sulfate ion is removed by nucleophilic substitution

asymmetric electrophilic addition

• an asymmetric alkene can cause multiple products as a reaction will favour one of the products over the other (selectivity)

• this selectivity is driven by carbocation intermediate stability, the more alkyl groups there are next to the positive charge, the more stable the intermediate is as it pushes electrons, stabilising adjacent positive

• tertiary carbocation > secondary carbocation > primary carbocation

• both reactions would occur, creating both products but there would be 1 major and 1 minor

electrophilic addition of alkenes

• an electrophile must have a positive charge to attracted to regions of negative charge, HBr would have a partially positive hydrogen end as bromine is more electronegative than hydrogen

• the hydrogen is attracted to the high electron density in the C=C bond, electrons from the pi-bond are attracted to the hydrogen, forming a covalent bond and pushing the electrons bonded before towards the bromine atom

• due to electrons from the old C=C bond now covalently bonded to the new H atom, this leaves 1 of the carbon atoms with a positive charge (carbocation)

• the negatively charged bromide ion is attracted to this carbocation, forming a dative covalent bond

Markovnikov’s rule

in an addition reaction of a halogen halide to an alkene, the halogen ends up bonded to the most substituted carbon atom

addition polymers

made in the reverse process to cracking

polymers

made up of repeating units (monomers)

processing waste polymers

• landfill sites are a common way of disposing plastics

• combusting in an incinerator disposes of the polymers

• used as organic feedstock to produce plastics and other organic compounds

photodegradable polymers

broken down into smaller pieces by sunlight, however it can cause problems such as in oceans, where fishes can ingest plastics

biodegradable polymers

broken down by microorganisms into CO₂ and water but needs to be the right environment

types of alcohols

• primary alcohols - has one carbon bonded to the functional group

• secondary alcohols - two carbons bonded to the functional group

• tertiary alcohols - 3 carbons bonded to the functional group

complete combustion of alcohols

when an alcohol is burned in an excess of oxygen, it’ll produce CO₂ and water

incomplete combustion of alcohols

if alcohols are burnt in insufficient oxygen, a mixture of CO, carbon and water is produced

ketones

the molecule you get when you oxidise a secondary alcohol, has a C=O bond and 2 other C-C bonds

aldehydes

the molecule you get when you oxidise a primary alcohol under distilation, has a C=O bond and atleast 1 other C-H bonds

carboxylic acids

the molecule you get when you oxidise an aldehyde under reflux using a reflux condenser which forces the aldehyde to be oxidised again

oxidation of alcohols

oxidation occurs by breaking C-H bonds, so primary alcohols can be oxidised twice, secondary can be oxidised once and tertiary can’t be oxidised

the usual oxidising agent is acidified potassium dichromate

dehydration of alcohols

elimination reactions where water is eliminated, requires an acid catalyst which protonates the -OH group to make it easier to eliminate the group

the acid catalyst is reformed when the H⁺ is lost as the alkene forms in the last step

substitution with halides

-OH group can be substituted with a halide group, making a haloalkane

haloalkane

halogenated alkane, polar molecule with halogen carrying negative charge and carbon carrying positive charge

nucleophile

negatively charged molecules that is attracted to a nucleus, such as molecules with lone pairs

electrophile

positively charged molecule that is attracted to a pair of electrons

nucleophilic substitution

the mechanisms for haloalkanes for hydroxide ions, ammonia, cyanide ions

reactivity of haloalkanes

I > Br > Cl > F

C-I bond is the weakest, C-F bond is the strongest

CFCs

chlorofluorocarbon, used in industry in the 20th century, escaped into the atmosphere and depleted the ozone layer

used in aerosols, coolants in fridges but were banned as they were damaging the ozone layer, alts like HFCs were used

ozone

O₃, less stable than O₂, formed from oxygen and UV light, present in low concentration, ozone layer contain its highest conc

CFCs are broken down by light (photolysis) in the atmosphere, creating chlorine radicals which reacts with O₃

mechanism for ozone depletion

synthetic route

route of reactions that will lead to the desired product and start from the starting materials

percentage yield

the ratio percentage of the actual yield obtained compared to the theoretical yield from calculations

percentage atom economy

percentage of reactant atoms that are transformed into the desired product

maximising percentages

• selecting reactions with no by-products

• selecting synthetic routes with fewer steps

infrared spectroscopy

• IR is used to identify certain bonds within a compound

• radiation is absorbed by any polar bond, making bonds vibrate with each frequency absorbed being specific to each bond

• frequency is normally reported as a wavenumber

wavenumber

represented as 1/λ

wavelength

represented as λ

fingerprint region

the section from 1500 to 500 cm^-1 which is usually full of small peaks and is specific to any molecules

uses of IR spectroscopy

• monitoring air pollution - measuring the level of pollutants

• breathalysers - determines how much ethanol is present, detecting alcohol content