topic 17 Flashcards
what is a chiral centre
a carbon atom with four different groups bonded to it so the molecule has no line of symmetry`
what is optical isomerism
a type of stereo isomerism chiral carbon atoms with non super imposable mirror images of each other
how are chiral centres indicated
with an asterisk
what are two different optical isomers called
enantiomers
how do enantiomers differ from eachother?
they rotate the plane of polarised light
what is a racemic mixture?
this is two enantiomers that exist in equal amounts( equimolar)
how do enentiomers of the same molecule differ
they rotate light by the same degree in opposite directions
what happens to light in the presence of a racemate
the plane of polarised light remains the same as the polarisation rotation is cancelled out
what are the two ways that nucleophillic substitution can occur
the negative charge can leave the chiral carbon first so that the nucleophile can attack from any direction .
the nucleophile could attack at the same time as the negative charge leaves so that it can only attack from one direction.
what is a carbonyl compound
a organic compouds containing a C=O group.and the functional group of -CO
what are the most common carbonyl groups
aldehydes and ketones
how are aldehydes produced
via the oxidation and distillation of primary alcohols
what do aldehydes react with to form carboxyllic acids
potassium dichromate
how are ketones formed
through the oxidisation and distillation of secondary alcohols
whats the main difference between aldehydes and ketones?
the positioning of the CO group
what is the positioning of the CO group on aldehydes
it is always on the end of an organic group and ends in -al
how many of each atom is there in the atom proponal
3 carbons, 6 hydrogens. and one oxygen atom.
what is tollens reagent used for
to distinguish between aldehydes and ketones
why is tollens reagent heated in a water bath and not under a flame
this is a safety precaution because aldehydes and ketones are very flammable
how do we test for aldehydes and ketones?
acidified potassium dichromate (K2Cr2O7)
what does potasssium dichromate show for the presence of aldehydes and ketones
it oxidises aldehydes. aldehydes turn from orange to green
no observations for ketones
what functinal group does carboxyll have
-COOH
what bonds do carboxyllic acids have
C=O(carbonyl group) bond and a -OH bond (a
whats the general formula for aldehydes?
RCHO
how are carboxylic acids formed from aldehydes
they are oxidised in the presence of acidified potassium dichromate (VI)
what is the general formula for ketones
RCOR
C=O
where is the carbonyl group on ketones
in between two hydrocarbon groups
what alcohols can be oxidised
primary and secondary
what happens when primary alcohols are heated in the presence of acidified potassium dichromate
an aldehyde is formed
what happens when secondary alcohols are oxidises in the presence of K2Cr2O7
ketones are formed
what is potassium dichromate used as and why
an oxidising agent because it is reduced in the reaction
what will be observed when a tertiary alcohol reacts with potassium dichromate
no colour change is observed
how can oxidation reactions to form carbonyl compounds from alcohols be reversed
they can be reversed through reduction reactions using lithium tetrehydridoaluminate in a dry ether
why is the reduction reaction carried out in a dry ether
because lithium aluminium hydride reacts violently with water
what is an arene
an aromatic compound that contains a benzene ring
do arene have low or high boiling points and why
low boiling points because they are non polar and cant be dissolved in water
do arenes have low or high melting points and why
high because of the high stability of the delocalised benzene ring
how are the pi bonds in benzene formed
there is a delocalised outer electron in the p-orbital in each carbon going into the centre to form an overlapping ring
why doesnt benzene undergo electrophillic addition
this would mean that the stable ring of electrons would be broken so instead electrophillic substitution occurs.
what is halogenation
an electrophillic substitution reaction where benzene reacts with a halogens in the presence of a catalyst
what is an example of a catalyst for halogenation reactions
FeBr3 iron(III) bromide
what functional group is linked with carboxyllic acids
-COOH
what is the general formula for grignards reagent and what is each letter
RMgX
R- alkyl group
Mg-magnesium
X-halogen
what is an alkyl group example
methyl ethyl
what is an amine
when an alkyl group replaces a hydrogen on ammonia
what is the purpose of grignards reagent
to lengthen the carbon chain
how do you distinguish between the classification of amine i.e primary secondary or tertiary
primary is only one alkyl group
secondary is two alkyl groups
tertiary is two alkyl groups that have displaced the hydrogen in ammonia
what is formed when grignards reagent is reacted with carbon dioxide and hydrolysed
a carboxylic acid
what is formed when grignards reagent is reacted with a carbonyl compound and hydrolysed?
an alcohol
