organic chemistry analysis

• How should you name secondary and tertiary amines? (same AND not same substituent groups)

  IF SAME: Dimethylamine IF NOT SAME: N-ethylmethylamine OR N, N-ethylmethylpropylamine
• What was wrong with Kekule's benzene structure and why?

  Doesn't react readily with halogens:

  - If it had 3 C=C bonds it's expected to react rapidly with Br2 by electrophilic addition.

  - It doesn't react readily as its e- density is too low

  - requires a catalyst and does so by electrophilic substitution. Bond length is intermediate:

  - C=C bonds are shorter than C-C bonds ∴ benzene should be irregular/deformed.

  - When bond length were measured. They were all the same, intermediate in length between single and double carbon-carbon bonds ∴ regular hexagonal shape.

  Enthalpy change of hydrogenation is less exothermic than expected:

  - Scientists measured it to be -120kJmol-1 for cyclohexene ∴ with benzene we'd expect -360kJmol-1.

  - Was measured to be -208kJmol-1 ∴ more stable than expected.
• Describe the π-ring in benzene and its consequences

  1) Sideways overlap of 6 p-orbitals (each containing 1 e-).

  2) Electron density above and below the plane spread over 6 12C's ∴ low electron density ∴ unable to polarise many molecules ∴ reactions require catalysts.

  3) Delocalised electrons meaning not attached to any single atom.

  
• Describe the nomenclature for substituted arenes

  - The lowest number is given to the lowest position of the alphabet: 1-bromo-4-chloro-2-ethylbenzene

  - When benzene is attached to an alkyl group with 7 or more carbons OR an alkyl with a functional group on it, it is the substituent: Phenylethanone 2-phenylhexane
• Give the 3 non-systematic arenes you need to know

  Benzoic acid Phenylamine Benzaldehyde
• What are the conditions, reactants, steps (with mechanism), type of reaction, and precautions of nitration of benzene?

  - Conditions/reactants: 50 °C, conc. HNO3 (nitric acid), conc. H2SO4 (sulfuric acid) catalyst.

  Form the nitronium ion... Stage 1: H2SO4 + HNO3 → HSO4- + H2NO3+ Stage 2: H2NO3+ → NO2+ + H2O Overall: HNO3 + H2SO4 → NO2+ + HSO4- + H2O

  React nitronium ion with benzene... The catalyst H2SO4 has reformed.

  - Type of reaction: electrophilic substitution. - Perform within a water bath ∵ reaction is exothermic. Any temperature too high will lead to polynitration rather than mononitration
• What are the reactants and steps (with mechanism) of the halogenation of benzene?

  - Reactants: halogen, halogen carrier (e.g., FeBr3/AlBr3 for bromination and FeCl3/AlCl3 for chlorination) as a catalyst.

  1. The halogen carrier polarises the halogen allowing it to react with the halogen carrier to form a positive electrophile. Br2 + FeBr3 → Br+ + FeBr4-

  2. React the electrophile with the benzene by electrophilic substitution... A positive electrophile has to be formed because benzene isn't very polarising.
• What are the conditions, reactants, and mechanism for Friedel-Crafts alkylation of benzene?

  - Conditions: heating under reflux.

  - Reactants: haloalkane with its halogen carrier (e.g., AlCl3 for CH3Cl).

  - Mechanism: electrophilic substitution,

  The CH3Cl + AlCl3 forms [CH3]+ + [AlCl4]-.
• How does the reactivity of methylbenzene and benzene compare?

  Methylbenzene is more reactive ∵ alkyl group releases electrons into π-ring ∴ increasing its electron density ∴ more polarising ∴ more reactive.
• How does benzene compare to other alkenes? (3)

  1) Bezene reacts by electrophilic substitution WHEREAS other alkenes react by electrophilic addition.

  2) Benzene has 6 delocalised e-'s in π-ring, 12 localised σ e-'s (2 in each C-C) WHEREAS other alkenes have 2 localised e-'s in π-bond and 2 in σ-bond in C=C. Benzene has 12 σ-bonds in total so 24 σ e-'s.

  3) Benzene requires a cataylst (eg, halogen carrier) ∵ its e- density is too low to polarise molecules WHEREAS other alkenes react readily ∵ high e- density.
• What is phenol?


  A benzene group with a -OH directly attached.

  
• What type of acid is phenol and how will it react with metals and bases?

  1. A weak acid.

  2. Reacts with metals and strong bases (eg, NaOH): THIS INCLUDES ANY OTHER AROMATIC COMPOUND WITH AN -OH.

  3. Too weak to react with weak bases (eg, Na2CO3) unlike carboxylic acids.
• How do alcohols react with bases?

  They don't because they're not acidic.
• How can you distinguish between phenol and a carboxylic acid?

  Carboxylic acids will react with a weak base (e.g., Na2CO3) leading to effervescence HOWEVER phenol will not.
• Describe the bromination of phenol (product, conditions, reactants)

  - Forms a white ppt (can be used to distinguish as the bromine decolourises).

  - No halogen carrier required, reacts readily, room temperature.

  
• Describe the nitration of phenol (with equation / diagrams)


  1. Reacts readily with dilute nitric acid to form a mixture:

  2. Reacts readily conc. nitric acid to produce 2,4,6-trinitrophenol:

  
• Why is phenol more reactive than benzene? (3)

  - The lone pair on the 16O partially delocalises into the π-ring (1)

  - Electron density increases (1)

  - Making it more polarising (1) as it includes dipoles making molecules polar.
• Give 2 uses of phenol

  - Antiseptic (used by Lister, called carbolic acid).

  - Detergents.

  - Dyes.
• Describe the 3 cases with 'directing groups' with examples

  "1. Unsubstituted ring - electron density constant so electrophiles are equally likely to react with any carbon.

  2. Substituted with electron-donating group (-OH or -NH2) - e-'s partially delocalise into the ring increasing its density at carbon 2, 4, 6 making them more likely to react.

  3. Substituted with electron-withdrawing group (-NO2) - no e-'s to delocalise, withdraws density from the ring, particularly carbons 2, 4, 6 making 3, 5 more likely to react. You can remember -NO2 as being an electron-withdrawing group since NO for ""NOT OPEN"".
• What is an acyl halide?

  Where R is an alkyl group and X is a halogen.

  
• What are the conditions, reactants, equation, and mechanism for Friedel-Crafts acylation of benzene?

  - Conditions: heating under reflux

  - Reactants: acyl halide and halogen carrier (e.g., CH3COCl for AlCl3)

  - Equation: CH3COCl + AlCl3 → [CH3CO]+ + [AlCl4]-

  - Mechanism: electrophilic substitution,
• What are carbonyl compounds?

  An aldehyde or ketone (containing C=O bond).

  
• Are carbonyls soluble and if so, why and which ones?

  - Yes as it can form hydrogen bonds with water. - The small ones.
• How is Tollens' Reagent used? (aka ammoniacal silver nitrate)

  Aldehydes are oxidised by Tollens' into carboxylic acids with Ag+ ions being reduced and coating inside of the test tube with a silver mirror: Ag+ (aq) + e- → Ag (s) and This cannot happen with ketones as they cannot be oxidised.
• How is Brady's Reagent used to identify carbonyls? And how does it react? (4)

  - Reacts with carbonyls to form a orange/yellow ppt (1)

  (2) - Recrystallise and determine melting point (3)

  - Compare to database values (4)
• How are alcohols formed from carbonyls? (without catalyst method) (reagents, type of reaction, mechanism, example equation)

  - NaBH4 is used as a source of hydride (H-) ions.

  - Type of reaction: reduction,

  - Mechanism:

  - Examples: CH3CH2CHO + 2[H] → CH3CH2CH2OH CH3COCH3 + 2[H] → CH3CH(OH)CH3 [H] just means some reducing agent.
• How can carbonyls be converted to alcohols? (with CATALYST) (type, reagents, conditions, example)

  - Type: reduction.

  - Reagents: H2 and nickel catalyst.

  - Conditions: high pressure.

  - Example: CH3CHO + H2 → CH3CH2OH
• What are nitriles?


  An organic compound that has a C≡N functional group

  
• How are nitriles named?


  The C≡N becomes part of the main chain (e.g., 2-hydroxy-2-methylpropanenitrile).
• How can carbonyls become hydroxynitriles and why would you do this? (with reagents, conditions, mechanism)

  - Reagents: sodium cyanide (NaCN) and dilute H2SO4 OR HCN.

  - Conditions: RTP.

  - Mechanism: nucleophilic addition.

  - In the case below, NaCN supplies CN- ions and H2SO4 supplies H+ ions.

  - This is useful for increasing the length of the carbon chain. Hydrogen cyanide (HCN) can be used as it dissociates in water to the ions but it's highly toxic.
• How does the strength of carboxylic acids vary with carbon chain length and why?

  - Increasing length means weaker acid.

  - Increasing the length pushes e- density onto the COO- making it more negative thus less stable thus less likely to form.
• What are salts of carboxylic acids called?

  Carboxylates. E.g, (CH3COO-)Na+ is called sodium ethanoate.

  
• What is different about methanoic acid to other carboxylic acids?

  It can be oxidised as its structure as it has an aldehyde group.

  
• How are esters named?

  The alcohol ends in -yl and is the prefix. The carboxylic acid ends in -anoate and is the suffix. This is called ethyl-methanoate.

  
• Describe the 2 types of esterification

  1. Esterification using acid catalyst: - Carboxylic acid + alcohol ⇌ ester + water - Sulfuric acid catalyst required for H+ ions - Heat under reflux

  2. Esterification using acid anhydrides: - Acid anhydride + alcohol → ester + carboxylic acid - Room temperature - Higher yield achieved

  
• What is an acid anhydride?

  Two carboxylic acids joined together. Ethanoic anhydride
• Give 2 ways esters can be hydrolysed (with conditions)

  1. Heating with HOT AQUEOUS ACID: - Use sulfuric acid catalyst under reflux. - Forms the original reactants. - CH3CH2CO2CH2CH3 + H2O ⇌ CH3CH2COOH + CH3CH2OH (reversible so doesn't give a good yield)

  2. Heating with HOT AQUEOUS ALKALI (saponification): - Use sodium hydroxide under reflux. - Forms a carboxylate salt and alcohol. - CH3CH2CO2CH3 + NaOH → (CH3CH2CO2-)Na+ + CH3OH The anion in the salt is resistant to attack by weak nucleophiles such as the alcohol so this reaction isn't reversible.

  
• How and why are acyl chlorides better than carboxylic acids?

  They are more reactive than carboxylic acids as Cl is a good leaving group.
• How are acyl chlorides formed? (with equation)

  - By reacting carboxylic acid using SOCl2 (thionyl chloride). - CH3COOH + SOCl2 → CH3COCl + SO2 + HCl
• How do acyl chlorides react with water?

  To produce a carboxylic acid and HCl (steamy white fume).