Organic Chemistry (topic 10/20) Flashcards
(69 cards)
1
Q
Homologous series
A
A series of compounds of the same family, with the same general formula, which differ from each other by a common structural unit.
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Structural isomers
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Compounds with the same molecular formula but different arrangements of atoms.
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Functional groups
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Single or groups of atoms that dictate the properties of a group of organic compounds. The reactive parts of molecules.
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Saturated compounds
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Contain single bonds only
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Unsaturated compounds
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Contain double or triple bonds.
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Alkanes
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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.
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Q
Alkenes
A
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.
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Q
Alcohols
A
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.
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Q
Halogenoalkanes
A
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.
10
Q
Polymers
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Addition polymers consist of a wide range of monomers and form the basis of the plastics industry.
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Benzene
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Benzene does not readily undergo addition reactions but does undergo electrophilic substitution reactions. Is an aromatic, unsaturated hydrocarbon.
12
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The different characteristics of a homologous series include:
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- 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
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Empirical formula
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Is the simplest whole-number ratio of atoms in a compound.
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Molecular formula
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Represents the real number of atoms and each type of atom in a compound.
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Full structural formulae
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All atoms and bonds between all atoms are shown.
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Condensed structural formulae
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Assumes certain bonds and therefore all atoms need not be shown. Easier to draw.
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Skeletal formulae
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Removes all atoms, leaving only a ‘skeleton’ of the molecule.
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Stereochemical formulae
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Shows the three-dimensional positions of atoms around a carbon.
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Alkynes
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- Functional group: alkynyl (triple carbon bond)
- Known as saturated compound
- General formula: CnH2n-2
Naming Alkynes
- [stem] + yne
ex. butyne, propyne, etc.
20
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Aldehydes
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- Functional group: CHO (aldehyde group)
General formula: CnH2n+1CHO
Naming aldehydes
- [stem] + al
ex. butanal, pentanal.
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Ketones
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- 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.
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Q
Carboxylic acids
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- Functional group: -COOH (carboxyl)
- General formula: CnH2n+1COOH
Naming Carboxylic acids
- [stem] + oic acid
ex. propanoic acid, butanoic acid, etc.
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Ethers
A
- 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.
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Esters
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- 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.
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Amines
- Functional group: -NH2
- General formula: CnH2n+1NH2
Naming Amines
- Primary Amines
- Secondary Amines
- Tertiary Amines
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Primary Amines
- Contain only one carbon connected to the nitrogen in the compound
- [stem] + amine
ex. propanamine, butanamine, etc.
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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.
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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.
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Amides
- Functional group: -CONH2 (carboxamide or amido)
- General formula: CnH2n+1CONH2
Naming Amides
- Primary Amides
- Secondary Amides
- Tertiary Amides
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Primary Amides
- Contain only one carbon bonded to the nitrogen
- [stem] + amide
ex. butanamide, propanamide, etc.
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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.
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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
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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
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Areles
- Functional group: phenyl
- General formula: C6H5
- Prefix: -phenyl or Suffix: -benzene
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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.
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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.
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Functional Group Isomerism
Occur when a molecule has the same molecular formula but two different functional groups.
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Volatility
How fast a molecule evaporates and is determined by the molecule’s boiling point.
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Three factors that influence the volatility and boiling point of a substance
1. Molar mass
2. Surface Area
3. Nature of a functional group
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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
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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
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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.
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Primary Alcohols
Have only one carbon atom directly bonded to carbon that is bonded to the functional group.
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Secondary alcohols
Have two carbon atoms directly bonded to carbon that is bonded to the functional group.
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Tertiary alcohols
Have three carbon atoms directly bonded to carbon that is bonded to the functional group.
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Primary Halogenoalkanes
Have only one carbon atom directly bonded to carbon that is bonded to the functional group. Similar to primary alcohols.
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Secondary Halogenoalkanes
Have two carbon atoms directly bonded to carbon that is bonded to the functional group. Similar to secondary alcohols.
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Tertiary Halogenoalkanes
Have three carbon atoms directly bonded to carbon that is bonded to the functional group. Similar to tertiary alcohols.
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Primary amides and amines
Have only one carbon atom directly bonded to the amide or amine functional group.
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Secondary amides and amines
Have two carbon atoms directly bonded to the amide or amine functional group.
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Tertiary amides and amines
Have three carbon atoms directly bonded to the amide or amine functional group.
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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.
1. Combustion reaction
2. Free-radical substitution reactions
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Combustion reaction
Alkanes undergo combustion in the presence of oxygen. They undergo two types of combustion:
1. 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.
2. 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
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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
1. 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
2. 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
3. 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* -> C2H6CH3*Cl* -> CH3Cl
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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.
1. Hydrogenation
2. Halogenation
3. Hydrogen halides
4. Hydration
5. Polymerisation
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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
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Halogenation
- Occurs when an alkene reacts with a halogen gas.
Ex. C2H4 + Br2 -> C2H4Br2
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Hydrogen halides
- Hydrogen halides react with alkenes to form halogenoalkanes.
Ex. C2H4 + HBr -> C2H5Br
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Hydration
- Alkenes react with water to form alcohols.
- The conditions for this reaction are steam and concentrated H2SO4.
Ex. C2H4 + H2O -> C2H5OH
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Polymerisation
- Polymerisation occurs when many alkenes join to form a polymer.
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Alcohol-related reactions
Alcohols are saturated and undergo substitution reactions as well as some other reactions.
Combustion of alcohols
Oxidation of alcohols
Esterification
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Combustion of alcohols
- Alcohols, in excess oxygen, combust to form carbon dioxide and water.
Ex. 2CH3OH + 3O2 -> 2CO2 + 4H2O
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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.
1. Primary alcohols
2. Secondary alcohols
3. Tertiary alcohols
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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.
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Oxidation of secondary alcohols
- Secondary alcohols form a ketone.
- The conditions for this reaction are heat under reflux with a suitable oxidising agent.
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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.
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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.
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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-.
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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
