Organic II- Topic 17 Flashcards
What is a chiral carbon atom/chiral centre?
A carbon atom with 4 different groups attached to it.
What are enantiomers?
Two different optical isomers of each other (mirror images) due to chiral compound
What is true of enantiomers?
Non-superimposable
What is optical activity?
The ability of a single optical isomer to rotate the plane of polarisation of plane-polarised monochromatic light in molecules containing a single chiral centre
What is a racemic mixture?
A mixture with equal quantities of each enantiomer of a chiral compound
What don’t racemic mixtures do?
Don’t rotate plane polarised light and the two enantiomers cancel each other’s light-rotating effect
Difference between Sn1 and Sn2 mechanisms
Sn1= single enantiomer reactant produces a racemic mixture of 2 optical isomers of each other ( won't rotate plane-polarised light) Sn2= single enantiomer reactant produces a single enantiomer product
if butan2ol solution proceeds via SN1 mechanism, why doesn’t it rotate plane-polarised light?
SN1 mechanisms produce racemic mixtures. Therefore there will be equal amounts of both isomers. The enantiomers light-rotating effects will cancel
How many steps are in an SN1 vs SN2 mechanism?
SN1 = 2 Step SN2= 1 Step
2,4 DNPH reacts with carbonyls and forms a ….. ….. ….
Bright orange precipitate.
How can the results of 2,4 DNPH and a carbonyl forming the identity of carbonyl compound?
Purification of org ppt by recrystallisation. Melting point of crystals can be compared to melting points of all known possible derivatives/ known values on database
How can you reduce carbonyls?
Using LiAlH4 in dry ether, to form:
aldehyde —-> primary alcohol
ketone—-> secondary alcohol
How do carbonyls react with Iodine in the presence of alkali?
form a yellow ppt of CHI3 and an antiseptic smell.
If something contains a methyl carbonyl group it must be either….
ethanal
or a ketone with at least 1 methyl group
Explain why it is necessary to use HCN and KCN in nucleophilic addition? [1]
As HCN alone provides insufficient CN-
Describe 3 tests that can be used to confirm the presence of an aldehyde and their positive results.
Warm with Tollens reagent, if carbonyl present then silver mirror will form.
Warm with Benedicts or Fehlings solution and if carbonyl present then blue solution forms red ppt
Warm with Acidified dichromate ions to form carbonxylic acid from the aldehyde (solution turns orange to green as the dichromate ions are reduced)
A chiral molecule is….
non-superimposable on it’s mirror image
