organic Flashcards
(21 cards)
optical isomerism
- a form of stereoisomerism
- have the same structural formula but different arrangement of atoms in space
optical isomers are ___ ___ of each other and have a ___ carbon atom
another word for optical isomers is ___
- mirror images
- chiral
- enantiomers
chiral
has 4 different groups attached yo a carbon atom
enantiomers are ___ ___ of each other and are ____
- mirror images
- non-superimposable
optically active isomers will rotate ___ ___ ___. this is a method of detecting an optically active compound
plane polarised light
plane polarised light only oscillates in one direction
optically active compounds will ___ plane polarised light
one enantiomer will ___ light clockwise, the other will ___ it anticlockwise (at same angle)
bc there is 2 enantiomers in the solution, might have more of one enantiomer than the other — so we get an overall oscillation
rotate
racemic mixture
when there is an equal amount of each enantiomer
racemates do not rotate plane polarised light — the 2 enantiomers rotate light in opposite directions and they cancel out
…
how is a racemic mixture (of a chiral product) made
- by reacting achiral substances together
- when the molecules react there is an even chance of forming each enantiomer — enantiomers made in equal amounts
(it is very difficult to adapt a reaction to only produce 1 enantiomer and it can be expensive)
molecules with planar profiles such as double bonds in C=C and C=O can make racemic products
these reactions occur where we have an attack on the carbonyl group (C=O) of unsymmetrical ketones and aldehydes
as the C=O part of a molecule is planar, the nucleophile can attack (the C) either from above or below, forming 2 different enantiomers
…
due to the ___ nature of C=O, there is an even chance of the nucleophile attacking from the ___ and the ___
this means we are likely to get a 50/50 mixture of both enantiomers and hence we produce a ___ ___ of products
as with all racemic mixtures, they do not rotate ___ ___ ___. the rotation of plane polarised light by either enantiomer ___ ___
- planar
- top
- bottom
- racemic mixture
- plane polarised light
- cancel out
ending of aldehydes (C=O on end)
ending of ketones (C=O in middle)
- -al
- -one
aldehydes can be readily oxidised however ketones can’t be oxidised
aldehydes are oxidised to carboxylic acids, using an oxidising agent [O]
…
(T) test to distinguish between an aldehyde and ketone
- add aldehyde/ketone to Tollens’ reagent
- place in hot water bath
*don’t use bunsen as aldehydes and ketones are flammable - aldehydes — Tollens’ is reduced to silver → silver mirror formed
- ketone — no silver mirror formed
how to make Tollens’ reagent [Ag(NH3)2]^+
silver nitrate (colourless) → add few drops of NaOH — pale brown ppt → add few drops of dilute ammonia until ppt dissolves
(F) test to distinguish between an aldehyde and ketone
- add aldehyde/ketone to Fehling’s solution
- place in hot water bath
*don’t use bunsen as aldehydes and ketones are flammable - Fehling’s solution is blue as it contains Cu^2+ ions
- aldehydes — Fehling’s solution goes from blue solution to brick red ppt (Cu2O)
- ketone — remains blue
what is Fehling’s solution
Cu^2+ ions dissolved in NaOH
what do Tollens’ reagent and Fehling’s solution act as when reacted with an aldehyde
oxidising agent
aldehydes and ketones can be reduced to form primary and secondary alcohols, respectively
reducing agents [H] such as NaBH4 dissolved in methanol and water can reduce aldehydes and ketones
it is the hydride ion (H^-) produced by the reducing agent that reduces aldehydes and ketones to alcohols — mechanism is the same for aldehydes and ketones
…
potassium cyanide reacts with carbonyl compounds (C=O) to produce hydroxynitriles (molecule contains OH and CN group) via a nucleophilic addition mechanism
potassium cyanide is used to produce the CN^- ions. when dissolved in acidic solution it dissociates to form K^+ and CN^- ions — KCN → K^+ + CN^-
KCN is a salt and salts breakdown very readily in solution
…
risks and precautions when using potassium cyanide
risks:
- KCN is an irritant and is very dangerous if ingested or inhaled
- when KCN reacts with moisture it can form the toxic gas, hydrogen cyanide
precautions:
- wear gloves while handling
- wear safety goggles at all times
- wear a lab coat to prevent clothing contamination
- use a fume cupboard to prevent exposure to toxic fumes
