Chapter 10: Organic Chemistry Flashcards
Distinguish between:
- Empirical formula
- Molecular formula
- Full structural formula
- Condensed structural formula
- Skeletal formula
- Empirical formula: simplest whole number ratio of the elements present in a compound
- Molecular formula: Total number of atoms of each element present in a compound (integer multiple of the empirical formula)
- Full structural formula: Shows all the atoms and bonds in a molecule
- Condensed structural formula: Simplest representation of how atoms are arranged in a molecule
- Skeletal formula: Shorthand representation of a molecule and its geometry (lines to represent bonds, angles to represent C atoms, and H atoms are assumed)
Explain what alkanes are
- Family of hydrocarbons
- General formula: CₙH₂ₙ₊₂
Define:
- Homologous series
- Functional group
Homologous series: Series of compounds with the same functional group, where one member differs from the next by a fixed structural unit (CH₂/mR=14)
- Members of the same homologous series: Have similar chemical properties and display a gradation in physical properties (MP/BP/solubility)
Functional group: Atom/group of atoms that gives a compound it is characteristic chemical properties (reactive part of the molecule)
Identify functional groups of:
- Alkanes
- Alkenes
- Alkynes
- Alcohols
- Ethers
- Aldehydes
- Ketones
- Carboxylic acids
- Esters
- Nitriles
- Amines
- Amides
- Alkanes: NIL (alkyl)
- Alkenes: C=C (alkenyl)
- Alkynes: C≡C (alkynyl)
- Halogenoalkanes: –Br/CI/I (halo)
- Alcohols: –OH (hydroxyl)
- Ethers: C–O–C (ether)
- Aldehydes: CH=O (carbonyl)
- Ketones: C=O (carbonyl)
- Carboxylic acids: COOH (carboxyl)
- Esters: COOC (ester)
- Nitriles: C≡N (nitrile)
- Amines: NH₂/NHR/NR₂ (amino)
- Amides: C=O(NH₂) (carboxamide)
State the molecular formula of benzene, draw its shape, name its functional group and state the term used to describe compounds containing/not containing a benzene ring
Benzene: C₆H₆ (phenyl functional group)
- Shape: Planar hexagonal ring with 6 Cs, 1 H atom attached to each
- Compounds containing a benzene ring: aromatic
- Compounds not containing a benzene ring: aliphatic
Explain trends in boiling point within a homologous series
Boiling points can only be compared within a homologous series, and not between series
- B.P increases along a series: higher mR = stronger LDF between molecules
- Alcohols have a higher B.P and greater solubility in water than alkanes: ability to form hydrogen bonds between alcohol molecules (B.P) and with water molecules (solubility)
Use IUPAC rules to name alkanes
- Assign prefix using longest carbon chain
- Use suffix “-ane” to indicate alkane
- Identify substituent groups/multiple identical substituent groups
- Assign substituent groups lowest possible number
- Arrange names of substituent groups in alphabetical order
Eg. 3,3,4-trimethylhexane
Distinguish between saturated and unsaturated compounds
Saturated compounds: contain only single bonds (alkanes)
Unsaturated compounds: contain double/triple bonds (alkenes and alkynes)
Use IUPAC rules to name alkenes and alkynes
- Indicate position of functional group by assigning lowest possible number in format “alk-x-ene”/”alk-x-yne”
(*lowest number assigned to functional group, not substituent group) - Add extra “a” if there are multiple functional groups present
Eg. 4-methylpent-2-ene
Eg. hexa-1,3,5-triene
Use IUPAC rules to name halogenoalkanes
- Indicate type and position of halo functional group in format “x-haloalkane”
(*lowest number assigned to functional group/substituent group according to alphabetical order)
Eg. 2-bromo-3-chloropentane
2-bromo-5-methylhexane
Use IUPAC rules to name alcohols
- Indicate position of –OH functional group in format “alkan-x-ol”
(*Lowest number assigned to functional group)
Eg. 5-methyl-hexan-3-ol
Use IUPAC rules to name ethers
- Name shorter carbon chain as a substituent group (methoxy-, ethoxy, propoxy, etc.)
Eg. 2-ethoxy-2-methylbutane
Use IUPAC rules to name aldehydes
- Carbon containing the functional group is C₁
- Format: “alkan-al”
Eg. 3-methyl-butanal
Use IUPAC rules to name ketones
- Indicate position of by assigning lowest number to functional group in format “alkan-x-one”
Eg. 4-methyl-pentan-2-one
Use IUPAC rules to name carboxylic acids
Carbon containing the functional group is C₁
- Format: “alkanoic acid”
Eg. 2,3-dimethylbutanoic acid
Eg. butanedioic acid
Use IUPAC rules to name esters
- Name carbon chain attached to the
–O in format “alkyl” - Name carbon chain attached to the =O in format “alkanoate”
Eg. Ethyl 2-methylpropanoate
Eg. 1-methylpropyl ethanoate
Distinguish between primary, secondary and tertiary alcohols, halogenoalkanes and amines
- Primary: Carbon attached to the functional group (alcohols/halogenoalkanes) or the N atom is attached to 1 other C atom
- Secondary: Carbon attached to the functional group (alcohols/halogenoalkanes) or the N atom is attached to 2 other C atoms
- Tertiary: Carbon attached to the functional group (alcohols/halogenoalkanes) or the N atom is attached to 3 other C atoms
Describe structural, positional and functional group isomerism
- Structural isomers: Same mR, different structural formula (position of substituent group changed, branching of straight-chains)
- Positional isomers: Same mR, different position of functional groups
- Functional group isomers: Same mR, different functional groups present
(Eg. Alcohols+ethers; aldehydes+ketones; carboxylic acids+esters)
Distinguish between the Kekulé benzene structure and the revised benzene structure
Kekulé benzene structure: Planar hexagonal ring of carbon atoms with a H atom joined to each C atom, and alternating single and double bonds joining the C together
Revised benzene structure: 1 C atom forms 3 bonds (2 with other C atoms and 1 with a H atom), allowing the remaining 6 electrons to form a delocalised system of electrons in the centre of the structure
Give both physical and chemical evidence for the revised structure of benzene
Physical:
- C–C bond lengths
(Revised structure: C–C bonds are equal in length and are intermediate in length between a C–C single bond and a C=C double bond)
(Kekulé benzene: C–C single bonds and the C=C double bonds would have varying lengths)
- Number of isomers of C₆H₄CI₂
(Only 3 isomers have been found, although the Kekulé benzene structure indicates that there should be 4)
Chemical:
- Enthalpy change of hydrogenation
(The Kekulé benzene structure suggests an enthalpy change of -360 KJ mol⁻¹. However, the actual enthalpy change value is lower, due to the added stability provided by the delocalised system of electrons)
- Reactions of benzene
(The presence of C=C double bonds Kekulé benzene structure suggests that benzene should be able to undergo addition reactions like all other unsaturated compounds. However, benzene does not, as this would destroy the delocalised system of electrons and the extra stability associated with it. Instead, benzene undergoes substitution reactions when reacted with halogens)
Explain why alkanes are volatile, insoluble in water and are generally unreactive
- Volatile: Non-polar molecule with only LDF between molecules
- Insoluble: Unable to form hydrogen bonds with water molecules
- Strong C–C bonds, making it energetically unfavourable to break them
- Non-polar C–C and C–H bonds that are unlikely to attract polar molecules/ions
Write equations for the complete and incomplete combustion of alkanes
- Complete combustion (excess oxygen):
Alkane + oxygen –> CO₂ + H₂O - Incomplete combustion (limited supply of oxygen):
Alkane + oxygen –> CO/C + H₂O
Write the general equation for the reaction of alkane with halogens, and state the condition for this reaction
General equation for free radical substitution:
CH₄ + CI₂ –> CH₃CI + HCI
Condition: UV light
Define a free radical and explain the free radical substitution mechanism
Free radical: Species with an unpaired electron, making them highly reactive
Initiation:
CI₂ –> 2 CI* (CI molecule broken down into 2 CI free radicals by UV light)
Propagation:
CI* + CH₄ –> HCI + CH₃*
CH₃* + CI₂ –> CH₃CI + CI* (restarting the propagation reaction and creating a chain reaction)
Termination:
CI* + CI* –> CI₂
CI* + CH₃* –> CH₃CI
CH₃* + CH₃* –> C₂H₆ (when free radicals collide to end the chain reaction)
Other multi-substituted products:
CI* + CH₃CI –> HCI + CH₂CI*
CH₂CI* + CI₂ –> CH₂CI₂ + CI*
CI* + CH₂CI₂ –> HCI + CHCI₂*
CHCI₂* + CI₂ –> CHCI₃ + CI*
CI* + CHCI₃ –> HCI + CCI₃*
CCI₃* + CI₂ –> CCI₄ + CI*
Explain why alkenes/alkynes have similar physical and chemical properties to alkanes, but are more reactive
Volatile, insoluble in water and generally unreactive: Alkenes/Alkynes are also non-polar molecules where only LDF exist between molecules
More chemically reactive:
- Breaking the second component of the C=C requires less energy than breaking a C–C single bond
- The C=C double bond (4 electrons) and the C≡C triple bond (6 electrons) are also electron-dense and likely to attract electrophiles (positive ions that are attracted to regions of high electron density and accept a pair of electrons to form a covalent bond)
Describe the addition reactions of alkenes
Mechanism: Electrophilic addition
- Alkenes and halogens:
Alkene + halogen –> Halogenoalkane - Hydrogenation (with heat and presence of nickel catalyst):
Alkene + H₂ –> Alkane
[Application: used to convert oil to margarine] - Alkenes and hydrogen halide (with heat):
Alkene + hydrogen halide –> Halogenoalkane - Catalytic hydration (with heat, high pressure and concentrated sulfuric acid):
Alkene + H₂O –> Alcohol
Describe an experiment to distinguish between alkenes and alkanes
Alkenes: Will decolourise bromine water (from orange to colourless), as alkenes will react with bromine (halogen) to become a halogenoalkane/an alcohol through the electrophilic addition mechanism
Eg. C₂H₄+ Br₂ –> CH₂H₄Br₂
C₂H₄+ Br₂ + H₂O –> C₂H₄BrOH + HBr
Alkanes + benzene: No colour change observed
Describe the addition polymerisation of alkenes
Addition polymerisation: when a large number of monomer molecules are joined together to form a long polymer chain
- Monomer vs repeating unit vs polymer
Describe the reaction for the combustion of alcohols
- Complete combustion (in excess oxygen): produces oxygen and carbon dioxide
Eg. C₂H₅OH + 3O₂ –> 2 CO₂ + 3 H₂O
Describe the oxidation reactions of alcohols
- Primary alcohols: Are first partially oxidised by an oxidising agent [Acidified potassium dichromate (VI) (K₂Cr₂O₇) or acidified potassium manganate (VII) (KMnO₄)] in the presence of heat to an aldehyde, before being fully oxidised to a carboxylic acid
*Colour change of the oxidising agent from orange to green (K₂Cr₂O₇) or purple to colourless (KMnO₄)
Eg. Ethanol –> Ethanal –> Ethanoic acid
–> The carboxylic acid product can be directly obtained by using KMnO₄ (stronger reducing agent), or by using a reflux set-up
–> While the aldehyde is not usually isolated, it can be distilled off using a distillation set-up before it can be oxidised further, since hydrogen bonds are not present within aldehydes, making their boiling points lower than their equivalent alcohols
- Secondary alcohols: Can be oxidised by the same oxidising agents to a ketone
Eg. Ethanol –> Ethanone - Tertiary alcohols: Resistant to oxidation
*Oxidation test can be conducted to distinguish primary/secondary alcohols from tertiary ones
Describe how alcohols and carboxylic acids can be reacted together to form an ester
Process: Esterification/condensation
Mechanism: Nucleophilic substitution
Alcohol + Carboxylic acid –> Ester + Water
Eg. Ethanol + propanoic acid –> Ethyl propanoate + water
Describe how halogenoalkanes undergo nucleophilic substitution
- Nucleophile: Molecule/anion with a lone pair of electrons, and is attracted to a positively charged region in a molecule, and donates an electron pair to form a covalent bond
[Nucleophile replaces halogen atom in a halogenoalkane] - Halogenoalkane + NaOH –> Alcohol + NaX
Eg. C₂H₅Br + NaOH –> C₂H₅OH + NaBr - Halogenoalkane + ammonia –> amine
Eg. C₂H₅Br + NH₃ –> C₂H₅NH₂ + HBr - Halogenoalkane + cyanide –> nitrile
Eg. C₂H₅Br + CN⁻ –> C₂H₅CN + Br⁻
