Chapter 17 - Organic Chemistry II Flashcards
(27 cards)
What is ‘chirality’ ?
When a compound and its mirror image are non-superimposable (optical isomerism)
What is a ‘chiral centre’ ?
A central carbon bearing four different substituents/groups which makes the molecule asymmetric/no line of symmetry
What is ‘plane polarised light’ ?
Monochromatic light that oscillates in only one plane
What is ‘unpolarised light” ?
Light that oscillates in all planes perpendicular to the direction of travel
What is a ‘polariser’ ?
A device that converts unpolarised light to plane-polarised light
What is a ‘polarimeter’?
A device used to measure the angle of rotation caused by a chemical - plane-polarised light passes through the analyser.
What are ‘enantiomers’ ?
Optical isomers that are mirror images of each other - they rotate the plane of polarisation of plane-polarised light
What is ‘optical activity’ ?
The ability of a single optical isomer to rotate the plane of polarisation of plane-polarised monochromatic light. An optically active molecule has no planes of symmetry
What is a ‘racemic’ mixture?
An equimolar mixture (50:50) of enantiomers of a chiral compound. The two enantiomers cancel out each others light rotating effect so the plane of polarisation of the plane-polarised light is not rotated
What is a ‘dimer’ ?
A molecule consisting of two identical molecules (monomers) linked together
What is ‘esterification’ ?
The reaction between a carboxylic acid and an alcohol in the presence of an acid catalyst to form an ester
e.g.
CH₃OH + CH₃COOH ⇌ CH₃COOCH₃ + H₂O (ᴄᴀᴛᴀʟʏsᴇᴅ ʙʏ ᴄᴏɴᴄ. H₂SO₄)
What is required in an esterification reaction involving hydrolysis?
The addition of a water molecule to break an ester bond
Is acidic hydrolysis reversible?
Yes, acidic hydrolysis is a reversible reaction but basic hydrolysis is irreversible
Irreversible reaction under basic conditions:
e.g. CH₃COOCH₃ + NaOH → CH₃COONa + CH₃OH
What is ‘condensation polymerisation’ ?
A reaction in which many monomers bond together to form a large molecule with the addition formation of a small molecule, usually water (or HCL, for example).
Forms polyesters and polyamides
What are ‘polyamides’ ?
Polymers with repeating units linked by amide bonds.
e.g. Wool and silk
What are ‘amide bonds’ ?
A type of chemical bond formed between a carbonyl group (C=O) and a nitrogen atom (N)
–> Commonly found in proteins and are referred to as ‘peptide’ bonds
How is the general structure of an amide represented as?
R-C(=O) - NR’R”
R, R’, R” : Represent either a hydrogen or an organic group
What is ‘saponification’ ?
Refers to the process of making soap - a basic hydrolysis of long-chain triglycerides to glycerol and corresponding salts of carboxylic acids
What is an ‘Sₙ1’ reaction?
- Nucleophilic substitution
- Unimolecular (one species in the slow step)
- Slow step: heterolytic fission of a halogenoalkane to give the carbocation, which is then attacked by a nucleophile
- If the reaction is performed on a chiral carbon centre, the carbocation intermediate is planar which means that it is susceptible to nucleophilic attack from both sides with equal probability
–> This leads to the formation of racemisation at a chiral centre. - Common with tertiary halogenoalkanes
What is an ‘Sₙ2’ reaction?
- Nucleophilic substitution
- Bimolecular (2 species in slow step)
- Single step mechanism
- Involves direct nucleophilic attack on halogenoalkane
- If the reaction is performed on a chiral centre, the reaction causes the inversion of the configuration so that the nucleophile approaches the carbon ONLY from the opposite side to the leaving group
- Common with primary halogenoalkanes
What is a primary (1°) halogenoalkane?
The carbon which is attached to the halogen is bonded to only one other alkyl group.
I.e the Carbon in C-X is bonded to ONE alkyl group
What is an exception to the rule on primary halogenoalkanes?
CH₃Br and other methyl halides are considered primary halogenoalkanes even though there are no alkyl groups attached the one carbon in the C-X bond.
What is a secondary (2°) halogenoalkane?
The carbon which is bonded to the halogen is also bonded to 2 other alkyl groups (they don’t have to be the same)
What is a tertiary (3°) halogenoalkane?
The carbon which is bonded to the halogen is also bonded to 3 other alkyl groups (they don’t have to be the same)
