1what is the definition of the following and how is it caused:
-optical isomerisim
- 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)
2What is a chiral centre?
A carbon atom bonded to 4 different groups in a tetrahedral structure (asymmetric)
3what is the definition of the following:
- Optical activity
the ability of an optical isomer to rotate the plane of plane polarised light
4Which molecules show optical activity?
molecules with a single chiral centre
5what are the directions in which plane-polarised light is rotated
clockwise - (D)
anticolock wise (L)
6what is the definition of the following:
- racemic mixture
A mixture containing equal amounts of both enantiomers
7how do you draw a cyclic ester
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
8Does a racemic mixture show optical activity?
No. The rotations caused by each enantiomer cancel each other out, resulting in no net rotation of plane-polarised light.
9What does the presence of a racemic mixture suggest about a reaction mechanism?
the reaction formed the chiral center in a planar intermediate, allowing attack from either side equally.
10Why does SN1 produce a racemic mixture?
SN1 forms a planar carbocation intermediate, allowing nucleophilic attack from either side equally, giving equal amounts of both enantiomers.
11What happens to optical activity in nucleophilic addition to carbonyl compounds (e.g., aldehydes/ketones)?
A new chiral centre is formed from a planar C=O, giving a racemic mixture.
12How does the lack of intermolecular hydrogen bonding affect the physical properties of aldehydes and ketones
Lower boiling points than alcohols of similar molar mass (because H-bonding is stronger than dipole–dipole interactions).
13How does hydrogen bonding with water affect solubility? (aldehydes/ketones)
-small aldehydes/ketones are highly soluble in water due to strong hydrogen bonding with water molecules.
-Hydrogen bonding is the predominant IMF
14Why does solubility decrease as chain length increases?
The hydrocarbon chain becomes larger and london forces become more dominant → reduced ability to hydrogen bond with water → lower solubility.
15What does Fehling’s/Benedict’s solution test for and the observations?
Aldehydes (NOT ketones).
Blue → brick-red precipitate of Cu₂O.
16What does Tollens reagent test for and the observations?
Aldehydes (NOT ketones).
Formation of a silver mirror (Ag metal).
17What does acidified pottasium dichromate (K2Cr2O7)test for and the observations?
Aldehydes (NOT ketones).
Orange → green as Cr₂O₇²⁻ is reduced to Cr³⁺.
18what is lithium aluminium hydride (LiAlH₄) used for
reduction [H+]
Aldehydes → primary alcohols
Ketones → secondary alcohols
19what are the conditions required for reduction of carbonyl's
lithium aluminium hydride (LiAlH4) + Dry ether
20What type of mechanism occurs when carbonyls react with HCN/KCN? (Draw it)
Nucleophilic addition.
21What does 2,4-DNPH test for and the observations?
Presence of any carbonyl group (aldehydes + ketones).
Formation of an orange precipitate
22How do you identify the carbonyl after a 2,4-DNPH test?
Recrystallise product → measure melting point → compare with database values.
23What does iodoform test for and the observations?
Methyl ketones (CH₃CO–R) + Alcohols that oxidise to methyl ketones (e.g., ethanol, 2-propanol)
Formation of a yellow precipitate of CHI₃
24Name carbonyl compounds that give a positive iodoform test
Ethanal (CH₃CHO)
Any methyl ketone, e.g., propanone, butanone.
25Why do carboxylic acids have higher boiling points than alcohols of similar size?
Because dimers are formed via two hydrogen bonds between molecules → more energy needed to break intermolecular forces.
26How does hydrogen bonding affect the solubility of carboxylic acids in water?
Small carboxylic acids can form hydrogen bonds with water → highly soluble.
27How can carboxylic acids be prepared from alcohols?
Primary alcohols can be oxidised using acidified potassium dichromate (VI)
Primary alcohol + 2[O] ---> Carboxylic acid
aldehyde + [O] ---> carboxylic acid
28How can carboxylic acids be prepared from nitriles
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
29what happens when LiAlH4 in dry ether reacts with carboxylic acids
Reduces carboxylic acids → primary alcohols.
RCOOH + 4[H] --> RCH2OH
30What happens when a carboxylic acid reacts with a base?
Forms a carboxylate salt and water.
Acid + base --> salt + water
Example:
CH3COOH + NaOH --> CH3COONa + H2O
31What happens when carboxylic acids react with PCl₅?3
Forms acyl chloride (RCOCl)
(alkanoyl chloride)
Example:
CH3COOH + PCl5 ---> CH3COCl + HCl + POCl3
Ethanoyl chloride
32How do carboxylic acids react with alcohols?
Forms esters in the presence of an acid catalyst (usually H₂SO₄).
Example:
CH3COOH + CH3CH2OH ---> CH3COOCH2CH3 + H2O
33What happens when an acyl chloride reacts with water?
A: Forms a carboxylic acid and HCl gas.
Example:
CH3COCl +H2O ---> CH3COOH +HCl
34What happens when an acyl chloride reacts with an alcohol?
Forms an ester and HCl gas.
Example:
CH3COCl + CH3CH2OH --> CH3COOCH2CH3 + HCl
35What happens when an acyl chloride reacts with concentrated NH₃?
Forms a primary amide and ammonium salt (white)
Example:
CH3COCl + 2NH3 ---> CH3CONH2 + NH4Cl
36What happens when an acyl chloride reacts with a primary amine (RNH₂)?
Forms a secondary amide and HCl.
Example:
CH3COCl + CH3NH2 ---> CH3CONHCH3 + HCl
37What happens when an ester undergoes acidic hydrolysis?
The ester reacts with hot dilute acid (H⁺/H₂O) → forms a carboxylic acid and an alcohol.
Example:
CH3COOOCH2CH3 + H2O ---> CH3COOH + CH3CH2OH
38What happens when an ester undergoes alkaline hydrolysis (Saponification)
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
39What is a polyester?
polymer formed by condensation polymerisation of diols (–OH) and dicarboxylic acids (–COOH), producing ester linkages (–COO–) and water as a by-product.
40How is Terylene formed?
ethylene glycol (HO–CH₂CH₂–OH) and terephthalic acid (HOOC–C₆H₄–COOH)
41Why is polyester a condensation polymer?
Because each bond formation releases a small molecule (water), unlike addition polymers where no by-product is formed.
42Features of condensation polymerisation for polyesters:
Formation of ester linkages
Requires di-functional monomers (diol + dicarboxylic acid)
By-product water is released
Produces high molecular mass polymer
43What does aqueous sodium hydrogencarbonate test for, and what is observed
-tests for the presence of a Carboxylic acid (COOH)
-fizzing