Aldehydes & Ketones Flashcards
How do we DISTINGUISH between ALDEHYDES & KETONS?
- Aldehydes can be OXIDISED into CARBOXYLIC ACIDS
- Ketones CANNOT be OXIDISED into a CARBOXYLIC ACID
Why can ALDEHYDES be OXIDISED into CARBOXYLIC ACIDS?
There is a HYDROGEN ATTACHED to the CARBONYL GROUP
How do we OXIDISE KETONES?
- We would have to BREAK the C-C BOND
- So they are NOT EASILY OXIDISED
How come there is a COLOUR CHANGE with OXIDATION reactions of ALDEHYDES?
- As an ALDEHYDE is oxidised, another compound is REDUCED
- So a REAGENT is used which causes the COLOUR CHANGE
What are the 2 REAGENTS that can be used to DISTINGUISH between ALDEHYDES & KETONES?
- Tollens’ Reagent
- Fehlings’ Solution
- KETONES DO NOT REACT WITH EITHER
What is TOLLENS’ REAGENT?
- COLOURLESS solution of SILVER NITRATE
- DISSOLVED in NH3(aq)
What VISIBLE OBSERVATION can be made when TOLLENS’ REAGENT reacts with an ALDEHYDE?
- If HEATED in a test tube with an ALDEHYDE
- A SILVER MIRROR is formed after a few minutes
What is FEHLINGS’ SOLUTION?
- A BLUE SOLUTION of complexed COPPER IONS (Cu II)
- DISSOLVED in NaOH
What VISIBLE OBSERVATION can be made when FEHINGS’ SOLUTION reacts with an ALDEHYDE?
- If HEATED with an ALDEHYDE the Cu2+ is REDUCED
- To a BRICK RED PRECIPITATE of Cu+O
How would you NOT HEAT KETONES & ALDEHYDES in a REACTION and why?
- NOT using NAKED FLAME
- Because both are FLAMMABLE
What can PRIMARY ALCOHOLS be OXIDISED into?
Primary Alcohol —> Aldehyde —> Carboxylic Acid
What can SECONDARY ALCOHOLS be OXIDISED into?
Secondary Alcohol —> Ketones
What are ALDEHYDES & KETONES?
- CARBONYL GROUPS
- With the FUNCTIONAL GROUP C=O
What is the GENERAL FORMULA for ALDEHYDES & KETONES?
Cn + H2n + O
What is the GENERAL FORMULA for CARBOXYLIC ACIDS?
Cn + H2N+1
What INTERMOLECULAR FORCES holds ALDEHYDES and KETONES together?
- The presence of CARBONYL groups means that there are VAN DE WAALS forces
- But also PERMANENT DIPOLE-DIPOLE interactions
What INTERMOLECULAR FORCES holds ALCOHOLS together?
- Van De Waals
- Permanent Dipole-Dipole Interactions
- Hydrogen Bonding
Describe the SOLUBILITY of ALDEHYDES and KETONES
- Although they CANNOT form H-BONDS with other CARBONYL compounds
- The O- can use its LONE PAIR to form a H-BOND with the H atoms in WATER
- ALL aldehydes and ketones CAN DISSOLVE in ORGANIC SOLVENTS
What VISIBLE OBSERVATION can you make when K2CR2O7 OXIDISES an ALDEHYDE or 1o ALCOHOL?
Orange —> Green
What is one reason why TOLLENS’ REAGENT is used as an [O] for ALDEHYDES rather than K2CR2O7?
It produces a CLEARER VISIBLE CHANGE
What can CARBOXYLIC ACIDS be REDUCDED into?
Carboxylic Acid —> Aldehyde —> Primary Alcohol
What can KETONES be REDUCED into?
Ketones —> Secondary Alcohols
What TWO SOLUTIONS are in FEHLING’S SOLUTION?
- FEHLING’S A - Contains Cu2+ (Blue)
- FEHLING’S B - Complexing agent that can form DATIVE BONDS with metal atoms / ions
When ALDEHYDES react with FEHLING’S SOLUTION, what is OXIDISED and what is REDUCED into what?
- Cu2+ is REDUCED into Cu+
- Aldehydes OXIDISE into CARBOXYLIC ACIDS
