Chapter 25 isomerism + Chapter 26 compounds containing carbonyl group

isomers definition

compounds with the same molecular formulae but different arrangement of atoms

structural isomers definition

molecules with the same molecular formula but different structural formula

stereoisomers definition

molecules with the same molecular formula but different arrangement of atoms in space

what type of isomers are optical isomers?

stereoisomers

what must all optical isomers have?

chiral carbon

what is a chiral carbon?

a carbon that is connected to 4 different substituents

optical isomers rotate…

plane polarised light

racemic mixture definition

contains and equal mixture of the two enantiomers, both equally rotate plane polarised light so no optical activity

what is optical activity

when a compound rotates plane polarised light

for nucleophilic addition when reducing aldehydes and ketones how is a racemic mixture formed and why does this not effect plane polarised light

• nucleophile attacks planar carbonyl group

• the product exists in two forms

• as nucleophile can attack from above or below

• so 2 enantiomers produced in equal amounts

• forms racemic mixture and both rotate plane polarised light in opposite directions equally so cancels out

state and explain how you could distinguish between 2 enantiomers

• plane polarised light

• rotates in opposite directions

general formula for aldehydes

RCHO

general formula for ketones

RCOR^’

what can oxidising agent be represented as

[o]

describe pathway for oxidation of primary alcohols

primary alcohols → aldehydes → carboxylic acids

describe pathway of oxidation for secondary alcohols

secondary alcohols → ketones

conditions for oxidation of primary alcohols to aldehydes

• acidified potassium dichromate

• simple distillation

conditions for oxidation of aldehydes or secondary alcohols

• reflux

• excess acidified potassium dichromate

what can we acidify potassium dichromate with

dilute sulphuric acid

reducing agent for aldehydes/ ketones

• NaBH4

through what mechanism can aldehydes and ketones be reduced

nucleophilic addition

what is another reagent used for nucleophilic addition other than NaBH4

KCN/HCN

why is KCN preferred

as HCN is toxic

products of KCN and aldehydes/ketones with nucleophilic addition

hydroxynitriles

products of NaBH4 and aldehydes/ketones with nucleophilic addition

alcohol

KCN needs an…

acid catalyst to provide hydrogen ions

nucleophile in NaBH4

Hydride ion

reducing agents can be represented as:

[H]

test for carboxylic acid

• sodium hydrogen carbonate

• effervescence produces CO2

tollens reagent half equation

[Ag(NH₃)₂]²⁺ + e^- → Ag + 2NH₃

carboxylic acid general formula

RCOOH

carboxylic acid + base

salt + water

carboxylic acid + metal carbonate

salt + water + carbon dioxide

carboxylic acid + alcohol

ester + water

• condensation reaction (esterification)

short chain esters use:

• Perfumes and food flavourings - sweet smells

• Solvents - low boiling points, polar compounds so readily dissolve, evaporate easily

• Plasticisers - make esters more flexible during polymerisation process

ester hydrolysis:

• acid hydrolysis

• base hydrolysis

acid hydrolysis conditions and definitions

splits ester into carboxylic acid and alcohol

CONDITIONS:

• Dilute sulphuric or hydrochloric acid

• Heat under reflux

base hydrolysis conditions and definitions

splits ester into carboxylate ion and alcohol

CONDITIONS:

• Sodium hydroxide

• Heat under reflux

biodiesel produced by

addition of 3 methanol + KOH catalyst

NAE (acyl chloride/ acid anhydride + ammonia)

amide

NAE (acyl chloride/acid anhydride + R-NH2)

N-substituted amide

NAE (acyl chloride/ acid anhydride + alcohol)

ester

NAE (acyl chloride/acid anhydride + water)

alcohol

NAE by product of acid anhydride

carboxylic acid

NAE by product of acyl chloride

HCl

what are acylation reactions

when a substance is reacted with acyl chloride

uses of acylation reactions

• cheaper

• less corrosive

• doesn’t react with water readily

• safer as by product HCl