Topic 15 A-D

- molecules that are non-superimposable mirror images of each other (enantiomers)

- caused as a result of chirlaty in molecules with a single chiral centre (carbon atom)

A carbon atom bonded to 4 different groups in a tetrahedral structure (asymmetric)

the ability of an optical isomer to rotate the plane of plane polarised light

molecules with a single chiral centre

clockwise - (D)
anticolock wise (L)

A mixture containing equal amounts of both enantiomers

e.g. 4- hydroxybutanoicacid

1- identify the hydroxy acid
2-remove H from -OH & remove OH from COOH
3-connect the oxygen to form a ring

No. The rotations caused by each enantiomer cancel each other out, resulting in no net rotation of plane-polarised light.

the reaction formed the chiral center in a planar intermediate, allowing attack from either side equally.

SN1 forms a planar carbocation intermediate, allowing nucleophilic attack from either side equally, giving equal amounts of both enantiomers.

A new chiral centre is formed from a planar C=O, giving a racemic mixture.

Lower boiling points than alcohols of similar molar mass (because H-bonding is stronger than dipole–dipole interactions).

-small aldehydes/ketones are highly soluble in water due to strong hydrogen bonding with water molecules.

-Hydrogen bonding is the predominant IMF

The hydrocarbon chain becomes larger and london forces become more dominant → reduced ability to hydrogen bond with water → lower solubility.

Aldehydes (NOT ketones).

Blue → brick-red precipitate of Cu₂O.

Aldehydes (NOT ketones).

Formation of a silver mirror (Ag metal).

Aldehydes (NOT ketones).

Orange → green as Cr₂O₇²⁻ is reduced to Cr³⁺.

reduction [H+]

Aldehydes → primary alcohols
Ketones → secondary alcohols

lithium aluminium hydride (LiAlH4) + Dry ether

Nucleophilic addition.

Presence of any carbonyl group (aldehydes + ketones).

Formation of an orange precipitate

Recrystallise product → measure melting point → compare with database values.

Methyl ketones (CH₃CO–R) + Alcohols that oxidise to methyl ketones (e.g., ethanol, 2-propanol)

Formation of a yellow precipitate of CHI₃

Ethanal (CH₃CHO)

Any methyl ketone, e.g., propanone, butanone.

Because dimers are formed via two hydrogen bonds between molecules → more energy needed to break intermolecular forces.

Small carboxylic acids can form hydrogen bonds with water → highly soluble.

Primary alcohols can be oxidised using acidified potassium dichromate (VI)

Primary alcohol + 2[O] ---> Carboxylic acid

aldehyde + [O] ---> carboxylic acid

Nitriles (–C≡N) are hydrolysed under acidic or basic conditions → produce carboxylic acids.

acidic: RCN + 2H2O + (H+) --> RCOOH + (NH4+)

basic:

RCN + (OH-) + H2O --> (RCOO-) + NH3
then acidify:
(RCOO-) + (H+) ---> RCOOH

Reduces carboxylic acids → primary alcohols.

RCOOH + 4[H] --> RCH2OH

Forms a carboxylate salt and water.

Acid + base --> salt + water

Example:

CH3COOH + NaOH --> CH3COONa + H2O

Forms acyl chloride (RCOCl)
(alkanoyl chloride)
Example:

CH3COOH + PCl5 ---> CH3COCl + HCl + POCl3

Ethanoyl chloride

Forms esters in the presence of an acid catalyst (usually H₂SO₄).

Example:
CH3COOH + CH3CH2OH ---> CH3COOCH2CH3 + H2O

A: Forms a carboxylic acid and HCl gas.

Example:
CH3COCl +H2O ---> CH3COOH +HCl

Forms an ester and HCl gas.

Example:

CH3COCl + CH3CH2OH --> CH3COOCH2CH3 + HCl

Forms a primary amide and ammonium salt (white)

Example:

CH3COCl + 2NH3 ---> CH3CONH2 + NH4Cl

Forms a secondary amide and HCl.

Example:

CH3COCl + CH3NH2 ---> CH3CONHCH3 + HCl

The ester reacts with hot dilute acid (H⁺/H₂O) → forms a carboxylic acid and an alcohol.

Example:

CH3COOOCH2CH3 + H2O ---> CH3COOH + CH3CH2OH

The ester reacts with aqueous OH⁻ (NaOH or KOH) → forms a carboxylate salt and an alcohol.

CH3COOCH2CH3 + (OH-) ---> CH3COO- + CH3CH2OH
then acidify:
CH3COO- + (H+) ---> CH3COOH

polymer formed by condensation polymerisation of diols (–OH) and dicarboxylic acids (–COOH), producing ester linkages (–COO–) and water as a by-product.

ethylene glycol (HO–CH₂CH₂–OH) and terephthalic acid (HOOC–C₆H₄–COOH)

Because each bond formation releases a small molecule (water), unlike addition polymers where no by-product is formed.

Formation of ester linkages

Requires di-functional monomers (diol + dicarboxylic acid)

By-product water is released

Produces high molecular mass polymer

-tests for the presence of a Carboxylic acid (COOH)
-fizzing