organic speedrun - incomplete Flashcards
What are enantiomers
Isomers that are related as object and mirror image
How do we know if an object shows optical activity?
It rotates the plane of polarised light
What is a racemic mixture
-an equine lad mixture if two enantiomers that has no optical activity
Which nucleophilic substitution reaction mechanism produces a racemic mixture?
Sn1
Reduction of an aldehyde? Explain conditions etc
Reducing reagent is LiAlH4 , both the carbonyl compound and the reagent are dissolved in dry ether
It goes to a primary alcohol
CH3CH2CHO + 2[H] —> CH3CH2CH2OH
Reduction of a ketone ?
-liAlH4 in dry ether
-gives a secondary alcohol
Same ting as aldehyde
Why are aldehydes easy to oxidise?
They have an hydrogen attached to the C=O.
Why are ketones resistant to oxidation
They don’t have that particular hydrogen atom attached to the C=O.
Reaction between aldehydes and acidified potassium dichromate?
Orange to green solution.
Forms a carboxylic acid
Condition : heat under reflux
Difference between sn1 and sn2 mechanism ?
Also explain optical activity in sn2
Sn1 an intermediate is formed whereas in sn2 the reaction occurs via a transition state
In sn2 if the reactant was chiral then during the reaction the opposite enantiomers would form and the product will show optical activity?
Compare the C=C and C=O bonds and what type of reactions take place?
The C=O bond is polarised because the O is more electronegative than carbon. The positive carbon atoms attracts nucleophiles.
However electrophiles are attracted to the C=C bond
The C=O bond is also stronger
Fehlings + aldehyde?
Deep blue to red precipitate
Tollens reagent + aldehyde?
Colourless to silver mirror. It often sticks to the test tube
Test for CH3CO group?
Reaction with iodine in alkaline solution (iodoform reaction)
+ve result - yellow ppt
-only aldehyde that gives a +ve result is ethanal
- only methyl ketones will give +ve result
Carbonyl compound + hydrogen cynaide? Plus optical activity?
- in this reaction involves a hydrogen atom attaching to the oxygen atom of the carbonyl group and a cyanide group attaching to the carbonyl group.
- product is called HYDROXYNITRILES
- Since the cynaide ion can attack from either above or below the plane equal amount of both enantiomers are formed
Test for C=O group?
Addition of 2,4-DNP
+ve result - bright orange ppt
Water is lost in this reaction and the 2,4 DNP adds across the C=O bond and the product contain an C=N
How can we use the 2,4 DNP reaction test for aldehydes and ketones,
the derivative (precipitate formed) is filtered, washed , recrystallised and then dried. Then by finding the melting point of the crystals you can compare it with tables of the melting points of all common aldehydes and ketone and find yours
