Organic Chemistry (topic 10/20) Flashcards
Homologous series
A series of compounds of the same family, with the same general formula, which differ from each other by a common structural unit.
Structural isomers
Compounds with the same molecular formula but different arrangements of atoms.
Functional groups
Single or groups of atoms that dictate the properties of a group of organic compounds. The reactive parts of molecules.
Saturated compounds
Contain single bonds only
Unsaturated compounds
Contain double or triple bonds.
Alkanes
Alkanes have low reactivity and undergo free-radical substitution reactions.
- Function group: alkyl
- Saturated compound
- General formula: CnH2n+2
Naming Alkanes
- [stem] + ane
ex. propane, butane, methane, etc.
Alkenes
Alkenes are more reactive than alkanes and undergo addition reactions. Bromine water can be used to distinguish between alkenes and alkanes.
- Functional group: alkenyl (double carbon bond)
- Known as unsaturated compound
- General formula: CnH2n
Naming Alkenes
- [stem] + ene
ex. hexene, butene, etc.
Alcohols
Alcohols undergo nucleophilic substitution reactions with acids (also called esterification or condensation) and some undergo oxidation reactions.
- Functional group: OH (hydroxyl group)
- General formula: CnH2n+1OH
Naming Alcohols
- [stem] + nol
ex. propanol, decanol, etc.
Halogenoalkanes
Halogenoalkanes are more reactive than alkanes. They can undergo (nucleophilic) substitution reactions. A nucleophile is an electron-rich species containing a lone pair that it donates to an electron-deficient carbon.
- Formed when a halogen is bonded to an alkyl group
- Functional group: R - X (R being the alkyl group and X being any halogen)
- General formula: CnH2n+1X
Naming Halogenalkanes
- Chloro- /bromo- /iodo- + [alkane]
ex. Bromoethane, iodobutane, etc.
Polymers
Addition polymers consist of a wide range of monomers and form the basis of the plastics industry.
Benzene
Benzene does not readily undergo addition reactions but does undergo electrophilic substitution reactions. Is an aromatic, unsaturated hydrocarbon.
The different characteristics of a homologous series include:
- Members have a functional group
- Molar mass of consequent members differ by 14 kJ mol-1
- Consequent members differ by CH2 group
- Members show gradual trend in physical properties
- Members have similar chemical properties
Empirical formula
Is the simplest whole-number ratio of atoms in a compound.
Molecular formula
Represents the real number of atoms and each type of atom in a compound.
Full structural formulae
All atoms and bonds between all atoms are shown.
Condensed structural formulae
Assumes certain bonds and therefore all atoms need not be shown. Easier to draw.
Skeletal formulae
Removes all atoms, leaving only a ‘skeleton’ of the molecule.
Stereochemical formulae
Shows the three-dimensional positions of atoms around a carbon.
Alkynes
- Functional group: alkynyl (triple carbon bond)
- Known as saturated compound
- General formula: CnH2n-2
Naming Alkynes
- [stem] + yne
ex. butyne, propyne, etc.
Aldehydes
- Functional group: CHO (aldehyde group)
General formula: CnH2n+1CHO
Naming aldehydes
- [stem] + al
ex. butanal, pentanal.
Ketones
- Functional group: -CO- (ketone)
- General formula: CnH2n+1COCxH2x+1 (where x and n are two positive intergers)
Naming Ketones
- [stem] + anone
ex. ethanone, hexanone, etc.
Carboxylic acids
- Functional group: -COOH (carboxyl)
- General formula: CnH2n+1COOH
Naming Carboxylic acids
- [stem] + oic acid
ex. propanoic acid, butanoic acid, etc.
Ethers
- Functional group: -O- (ether)
- General formula: CnH2n+1OCmH2m+1 (where m and n are two positive integers)
Naming Ethers
- [stem of shorter carbon chain] + oxy + [stem of longer carbon chain] + ane
ex. methoxypropane, ethoxyethane, etc.
Esters
- Functional group: -COO- (ester)
- General formula: CnH2n+1COOCmH2m+1 (where n and m are two positive integers)
Naming Esters
- [stem of alcohol] + yl + [stem of carboxylic acid] + noate
ex. methyl methanoate, ethyl propanoate, etc.
Amines
- Functional group: -NH2
- General formula: CnH2n+1NH2
Naming Amines
- Primary Amines
- Secondary Amines
- Tertiary Amines
Primary Amines
- Contain only one carbon connected to the nitrogen in the compound
- [stem] + amine
ex. propanamine, butanamine, etc.
Secondary Amines
- Contain two carbons connected to the nitrogen in the compound
- N-[stem of shorter carbon chain] + yl + [stem of longer carbon chain] + amine
ex. N-methylbutanamine, N-ethylpropanaimine, etc.
Tertiary Amines
- Contain three different carbon bonds connected to the nitrogen in the compound.
- N-[stem of shortest carbon chain] + yl + N-[stem of shorter carbon chain] + yl + [stem of longest carbon chain] + amine
ex. N, N-diethylpropanamine, N-propyl-N-butylhexanamine.
Amides
- Functional group: -CONH2 (carboxamide or amido)
- General formula: CnH2n+1CONH2
Naming Amides
- Primary Amides
- Secondary Amides
- Tertiary Amides
Primary Amides
- Contain only one carbon bonded to the nitrogen
- [stem] + amide
ex. butanamide, propanamide, etc.
Secondary Amides
- Contain two carbon atoms bonded to the nitrogen
- N-[stem of shorter carbon chain] + yl + [stem of longer carbon chain] + amide
ex. N-butylhexanamide, N-propylpentanamide, etc.
Tertiary Amides
- Contain three different carbon bonds connected to the nitrogen in the compound
- N-[stem of shortest carbon chain] + yl + N-[stem of shorter carbon chain] + yl + [stem of longest carbon chain] + amide
ex. N, N-diethylpropanamide, N-propyl-N-butylhexanamide
Nitriles
- Functional group: -CN (nitrile)
- General formula: CnH2n+1CN
Naming Nitriles
- The carbon from the nitrile group counts as the first carbon of the chain
- [stem] + ane + nitrile
ex. ethanenitrile, propanenitrile
Areles
- Functional group: phenyl
- General formula: C6H5
- Prefix: -phenyl or Suffix: -benzene
Structural Isomers
Compounds with the same molecular formula but a different structure and arrangement of atoms. Have the similar chemical properties but different physical properties such as melting and boiling points.
Chain Isomers
Occur when a molecule can have its functional group in different positions in the molecule. When it can alter its longest carbon chain.
Functional Group Isomerism
Occur when a molecule has the same molecular formula but two different functional groups.
Volatility
How fast a molecule evaporates and is determined by the molecule’s boiling point.
Three factors that influence the volatility and boiling point of a substance
- Molar mass
- Surface Area
- Nature of a functional group
Molar mass influencing the volatility and boiling point of a substance
- As molar mass increases
- Strength of London Dispersion forces increase
- Energy required to break the intermolecular bonds between between a molecule increases
- Boiling point increases
Surface Area influencing the volatility and boiling point of a substance
- Branch-chained isomers have a smaller surface area and so they have less contact with other molecules.
- Strength of London Dispersion forces decreases compared to straight-chain isomers.
- Energy required to break the intermolecular bonds between a molecule decreases.
- Boiling point decreases
Nature of a functional group influencing the volatility and boiling point of a substance
- Polar functional groups result in stronger dipole-dipole interactions and therefore require higher amounts of energy to break the bonds, leading to higher boiling points
- Some molecules, such as alcohols and carboxylic acids can form hydrogen bonds and therefore have even higher boiling points.
Primary Alcohols
Have only one carbon atom directly bonded to carbon that is bonded to the functional group.
Secondary alcohols
Have two carbon atoms directly bonded to carbon that is bonded to the functional group.
Tertiary alcohols
Have three carbon atoms directly bonded to carbon that is bonded to the functional group.
Primary Halogenoalkanes
Have only one carbon atom directly bonded to carbon that is bonded to the functional group. Similar to primary alcohols.
Secondary Halogenoalkanes
Have two carbon atoms directly bonded to carbon that is bonded to the functional group. Similar to secondary alcohols.
Tertiary Halogenoalkanes
Have three carbon atoms directly bonded to carbon that is bonded to the functional group. Similar to tertiary alcohols.
Primary amides and amines
Have only one carbon atom directly bonded to the amide or amine functional group.
Secondary amides and amines
Have two carbon atoms directly bonded to the amide or amine functional group.
Tertiary amides and amines
Have three carbon atoms directly bonded to the amide or amine functional group.
Alkane-related reactions
Since Alkanes are saturated hydrocarbons, they undergo substitution reactions.
Carbon-hydrogen bond is non-polar which means it is more stable since charge distribution is not unequal.
- Combustion reaction
- Free-radical substitution reactions
Combustion reaction
Alkanes undergo combustion in the presence of oxygen. They undergo two types of combustion:
- Complete combustion
- This occurs in the presence of excess oxygen. Ex. C3H8(g) + 5O2(g) -> 3CO2(g) + 4H2O(l)
- It results in carbon dioxide and water.
- Incomplete combustion
- This occurs in the presence of insufficient oxygen. Ex. C3H8(g) + 7O2(g) -> 6CO(g) + 8H2O(l)
- It results in the formation of carbon monoxide/carbon and water
Free radical substitution reactions
- Alkanes react with halogens in free-radical substitution reactions
- The condition for this reaction is UV light
- The reaction can be divided into 3 parts
- Initiation
- In this step, the chlorine (or any halogen) undergoes photochemical homolytic bond fission and forms radicals of chlorine, which are very reactive.
Ex. Cl2 -> 2Cl
- In this step, the chlorine (or any halogen) undergoes photochemical homolytic bond fission and forms radicals of chlorine, which are very reactive.
- Propagation
- In this step, the free-radical chlorine reacts with an alkane to form an alkane radical.
- This alkane radical reacts with a chlorine free-radical again to form a halogenoalkane.
Ex. Cl* + CH4 -> CH3* + HCl
CH3* + Cl2 -> CH3Cl + Cl - The net amount of radicals remains the same as a radical is used and a radical is produced in every reaction
- Termination
- In this step, two free-radicals combine again to form the original molecules and new molecules.
- All free-radicals are terminated
Ex. Cl* + Cl* -> Cl2
CH3* + CH3* -> C2H6CH3Cl -> CH3Cl
- Initiation
Alkene-related reactions
Alkenes are unsaturated and undergo addition reactions where the double-bond is broken.
In addition reactions, two smaller molecules react to form one bigger molecule.
- Hydrogenation
- Halogenation
- Hydrogen halides
- Hydration
- Polymerisation
Hydrogenation
- Occurs when an alkene reacts with hydrogen to form an alkane.
- The conditions for this reactions are Ni and 150 degrees C.
Ex. C2H4 + H2 -> C2H6
Halogenation
- Occurs when an alkene reacts with a halogen gas.
Ex. C2H4 + Br2 -> C2H4Br2
Hydrogen halides
- Hydrogen halides react with alkenes to form halogenoalkanes.
Ex. C2H4 + HBr -> C2H5Br
Hydration
- Alkenes react with water to form alcohols.
- The conditions for this reaction are steam and concentrated H2SO4.
Ex. C2H4 + H2O -> C2H5OH
Polymerisation
- Polymerisation occurs when many alkenes join to form a polymer.
Alcohol-related reactions
Alcohols are saturated and undergo substitution reactions as well as some other reactions.
Combustion of alcohols
Oxidation of alcohols
Esterification
Combustion of alcohols
- Alcohols, in excess oxygen, combust to form carbon dioxide and water.
Ex. 2CH3OH + 3O2 -> 2CO2 + 4H2O
Oxidation of alcohols
- Alcohols can be oxidised by oxidising agents such as acidified potassium dichromate [Cr2(O7)^2-], which is accompanied with a color change from orange to green as it is reduced to Cr^3+.
- Depending on the type of alcohol, different products are formed.
- Primary alcohols
- Secondary alcohols
- Tertiary alcohols
Oxidation of primary alcohols
- Primary alcohols undergo partial oxidation to form an aldehydes, after which they form a carboxylic acid.
- For these reactions, heat under reflux (to allow the alcohol and the oxidising agent to remain in contact for a longer time) is required with an excess of the oxidising agent.
Oxidation of secondary alcohols
- Secondary alcohols form a ketone.
- The conditions for this reaction are heat under reflux with a suitable oxidising agent.
Oxidation of tertiary alcohols
- Since they have no hydrogen atom directly bonded to the carbon atom that is bonded to the functional group, they do not undergo oxidation.
Esterification
- Esters are formed when an alcohol reacts with a carboxylic acid.
- In the name of the compound, the alkyl group of the alcohol comes first and the alkyl group of the carboxylic acid comes second.
- So, methanol and propanoic acid would form methyl propanoate.
Halogenoalkane-related reactions
Halogenoalkanes undergo substitution reactions.
A nucleophile is a species that is rich in electrons and has a lone pair of electrons, which means it is attracted to molecules with positive charge.
Nucleophilic substitution reaction to form alcohol
- In the halogenoalkane molecule, the halogen is a nucleophile due to the three lone pairs that it has.
- So, the carbon (which has a partial positive charge in the bond) undergoes heterolytic bond fission with the halogen where the halogen takes the bonding electrons.
- In general, in heterolytic bond fission, a bond breaks and one atom takes both the bonding electrons from the covalent bond. This forms oppositely charged ions.
- The reaction that takes place is known as a nucleophilic substitution reaction as the nucleophilic halogen is separated from the halogenoalkane and replaced by another nucleophilic ion.
- The nucleophilic halogen gains a negative charge after being separated as it takes both the bonding electrons.
- Strong bases or alkalis like NaOH are reacted with halogenoalkanes as they contain a nucleophilic species, OH- , which has a lone pair of electrons (hence nucleophilic).
- The OH- ion substitutes the halogen, and the halogenoalkane is converted to an alcohol.
- The reaction conditions for the conversion of a halogenoalkane to an alcohol are heat and a dilute solution of sodium or potassium hydroxide.
CH3CH2CH2Cl + NaOH -> CH3CH2CH2OH + NaCl
- As seen by the reaction, the halogenoalkane 1-chloropropane is converted to the primary alcohol propanol with the by-product of sodium chloride as chlorine is substituted for OH-.
Benzene-related reactions
- Benzene undergoes substitution reactions to maintain its stable structure.
- The ring of delocalised electrons in benzene represent a region of electron density.
- Therefore, electrophilic species are attracted to benzene due to its ring of delocalised electrons.
- So, benzene undergoes electrophilic substitution reactions.
- An electrophile is an electron-deficient species that has a partial positive or completely positive charge.
Nitration
- Benzene reacts with the nitronium ion (NO2)+ in an electrophilic substitution reaction to form nitrobenzene.
- In this reaction, the nitronium ion acts as the electrophile.
- The catalyst for this reaction is concentrated sulfuric acid (H2SO4)
Halogenation
- Benzene also undergoes electrophilic substitution reactions with halogens.
- For example, chlorine reacts with benzene to form chlorobenzene and hydrogen chloride. The catalyst for this reaction is aluminium chloride.
- In general, halogens react with benzene to form chloro- , fluoro- iodo- , bromo- benzene with the byproduct of a hydrogen halide (the halide that benzene reacted with). The catalyst, in general, will be aluminium halide (the halide that reacted with benzene).
Combustion of benzene
- Like all hydrocarbons, benzene also undergoes combustion in the presence of excess oxygen.
2C6H6 + 15O2 -> 12CO2 + 6H2O
