Optical isomerism and carbonyl compounds

Define stereoisomers

Same structural formula atoms arranged differently

What is a chiral carbon

Carbon with 4 different atoms/groups attached

Tetrahedral arrangement is possible so that one mirrors another l

How do you distinguish between aldehydes and ketones 

Tollens reagent-colourless silver nitrate dissolved in aqueous ammonia 

[Ag(NH3)2]+

If heated with aldehyde = silver mirror 

Fehlings solution 

Blue complex copper ions dissolved in NAOH 

If aldehyde brick red precipitate

How do you form hydroxy nitriles (two reagents)

Nucleophillic addition 

KCN + aldehyde/ketone 

Followed by dilute acid 

If HCN no acid needed because H+,dangerous slow

Explain why hydroxynitriles produces a racemic mixture 

Carbonyl group is planar

Nucleophile can attack on either side with equal probability 

To produce racemic mixture 

Equal amounts of to enatiomers 

Define racemic mixture

Equal mixture of both enatiomers

Describe how separate samples of each of these enatiomers could be distinguished 

Use plane polarised light 

See if they rotate light in opposite directions 

How do you reduce aldehydes/ketones and what do they produce 

Sodium tetrahydrideoborate

NaBH4

Aldehydes =reduced to primary alcohols 

Ketones = secondary alcohols 

Hazards of KCN

Toxic 

Fume cupboard

Risk of HCN gas released from solution

Heat in water bath as organic compounds flammable

Why does compound NOT show sterioisomerism

No chiral centre

Not 4 different groups attached to carbon 

By considering the mechanism (reduction with NaBH4) explain why the product has no effect on plane polarised light 

Nucleophile attacks compound 

Carbonyl group planar

H- attacks from either side with equal probability 

exists in two chiral forms 

Racemic mixture /equal amounts of each 

Enatiomers rotate plane polarised light equally

So effects cancel 

State relationship between two chiral molecules with the same structural formula 

Non superimposable mirror images 

How to test for carboxylic acid+observations

React with carbonate (caco3/naco3/nahco3)

Effervescence -bubbles of co2

What is the relationship between solubility and carboxyllic acid chain length

R group length increases

Less soluble 

More hydrocarbon chain which is non polar so does not form hydrogen bonds 

What reaction forms an esters 

Esterification 

Reaction between carboxyllic acid and alcohol 

Concentrated H2SO4 catalyst 

Reversible 

Uses of esters 

Solvents 

Plasticiser -weaken IMF polymer chains making them flexible 

Food flavourings +perfume 

What do you form from acid/base hydrolysis  of ester

Acid-carboxylic acid 

Base-carboxylate ions (non reversible higher yield ,reflux