Unit 4 Organic Flashcards
How do you make Tollen’s reagent
Silver nitrate and aqueous ammonia
What gives a positive result for Tollen’s? - observation
Aldehydes- silver mirror forms
What gives a positive result for Fehling’s?
Aldehydes- solution changes from blue to red due to the formation of a red precipitate
Optical Isomerism
Occurs in carbon compounds with 4 different groups of atoms attached to a chiral/asymmetric carbon
What is optical activity?
The ability of an optical isomer to rotate plane polarised light
Racemic mixture
A mixture containing a 50/50 mixture of two enantiomers
Describe the optical activity of a racemic mixture
- A racemic mixture will have no effect on plane polarised light
- Each enantiomer will rotate light in opposite directions by the same degree
- no overall reaction since enantiomers are in equal quantities
Aldehyde + acidified potassium dichromate
- Aldehydes are oxidised
- colour change from orange to green
Ketone + acidified potassium dichromate
- ketones do not react, do not get oxidised
- solution remains orange
What kind of halogenoalkanes undergo SN1 reactions
Tertiary Halogenoalkanes
What kind of halogenoalkanes undergo SN2 reactions
Primary and secondary halogenoalkanes
Aldehyde –> Primary Alcohol
Reagent: LiAlH4 in dry ether
Ketone –> Secondary Alcohol
Reagent: LiAlH4 in dry ether
What qualitative test can be used to test for the presence of a carbonyl group (and positive result)
- React with 2,4DNPH/ Brady’s Reagent
- Orange precipitate
What kind of reaction will form a racemic mixture? Explain
SN1:
- the bond around the carbocation is planar
- equal chance of the nucleophile attacking from either above or below
- produces enantiomers in equal proportions –> racemic mixture
