organic 3 weak areas

describe kekule model of benzene

• benzene is made up of a planar (flat) ring of carbon atoms with alternating single and double bonds between them.

• each carbon atom is also bonded to one hydrogen atom.

• benzene molecule was constantly flipping between two forms (isomers) by switching over the double and single bonds

why is kekule model of benzene wrong

• you’d expect benzene to have three bonds with the length of a C–C bond and three bonds with the length of a C=C bond

• However X-ray diffraction studies have shown that all the carbon‑carbon bonds in benzene have the same length

describe delocalised model of benzene

• each carbon atom forms three s‑bonds — one to a hydrogen atom, and one to each of its neighbouring carbon atoms.

• These bonds form due to head-on overlap of their atomic orbitals.

• Each carbon atom then has one remaining p‑orbital, containing one electron, which sticks out above and below the plane of the ring.

• These p‑orbitals on each of the carbon atoms overlap sideways to form a ring of p‑bonds that are delocalised around the carbon ring.

• The delocalised p‑bonds are made up of two ring-shaped clouds of electrons — one above and one below the plane of the six carbon atoms.

• All the bonds in the ring are the same — so, they’re all the same length.

• 5) The electrons in the rings are said to be delocalised because they don’t belong to a specific carbon atom. They are represented as a circle inside the ring of carbons rather than as double or single bonds.

why dont benzene undergo elctrophillic addition reaction?

• the delocalised p‑bonds spread out the negative charge and make the benzene ring very stable.

• so benzene is unwilling to undergo addition reactions which would destroy the stable ring.

• more evidence supporting the delocalised model.

• in alkenes, the p-bond in the C=C double bond is an area of localised high electron density which strongly attracts electrophiles. In benzene, this attraction is reduced due to the negative charge being spread out.

• so benzene prefers to react by electrophilic substitution

benzene + O2

• co2 + h20

• observation : smoky flame

• there is little o2 to burn benzene completely so carbon atoms stay as carbon and form particulates of soot in the hot gas making the flame smoke

what does a halogen carrier do?

• accepts a lone pair of electrons from a halogen atom on an electrophile.

• As the lone pair of electrons is pulled away, the polarisation in the molecule increases and sometimes a carbocation forms.

• This makes the electrophile stronger

reagents for alkylation of benzene and draw the mechanism

• halogenoalkane + halogen carrier (aluminum chloride-AlCL3) + reflux

reagents for acylation of benzene and draw mechanism

• acyl chloride + heated under reflux in a non-aqueous solvent (like dry ether)

reagents for nitration of benzene and draw mechanism

• warm benzene with concentrated nitric acid and concentrated sulfuric acid

reagents to make aliphatic amines from halogenoalkane

• halogenolakne

• excess ethanolic ammonia

reagents required for both methods of reducing a nitrile to an primary amine

expensive method:

• lithium aluminum hydride (LiAlH4)

• in a non‑aqueous solvent ( dry ether)

• dilute acid.

industrial method:

• hydrogen gas

• metal catalyst, such as platinum or nickel

• high temperature and pressure (catalytic hydrogenation)

reagents for reducing a nitro compound to make a aromatic amine

• tin

• concentrated HCL

• reflux

• naOH

reagents and observations for the acylation of amines

• reagent: acyl chloride (ethanoyl chloride + concentrated aqueous solution of the amine)

• products: N substituted amide + salt

• observation: solid, white mixture of the products.

products and reagents for acyl chloride + ammonia or a primary amine

acyl chloride + ammonia

• concentrated ammonia

• room temperature

• product: primary amide

acyl chloride + primary amine

• primary amine

• room temperature

• product: N-substituted amide

reagents to make polyamides and draw the mechanism

• dicarboxylic acids + diamines

conditions required for hydrolysis of protein to amino acids and draw the mechanism

• Hot aqueous 6 mol dm–3 hydrochloric acid

• heated under reflux for 24 hours

• product: ammonium salts of the amino acids - neutralised using a base.

• chromatography to identify the amino acid monomers

reagents for the condensation polymerisation of polyesters and draw mechanism

• dicarboxylic acids + diols

reagents for making Grignard reactants

• refluxing

• halogenoalkane with magnesium

• in dry ether.

reagent and condition for making a carboxylic acid using Grignard reagents

Q: Butanoic acid can be synthesised from bromopropane in three steps. Give the reagents and conditions needed for each step, and the product formed at each stage of the synthesis.

• 1. bubble thru CO2 (reagent) + dry ether

• 2. dilute HCL

product, reagents and conditions for Grignard reagents with carbonyl compounds

• product: alcohol

• 1. carbonyl compound is added to the Grignard reagent in dry ether,

• 2. dilute acid is added to the reaction mixture