organic 2 p2 Flashcards
what property must a carbon atom have for the molecule to display optical isomerism about that carbon atom?
4 different substituents attached to one carbon
what are the similarities and differences between two optical isomers?
same atoms and bonds, but they are non superimposable mirror images of one another NOT IDENTICAL in chemical properties necessarily
differ in the way they rotate plane polarised light - rotate by the same angle but in different directions
what word to used to describe optically active molcules?
chiral
example of a chiral molecule - lactic acid
what are a pair of isomers called?
enantiomers
what is the chiral centre?
the carbon that has four different substituents attached to it
denoted by a star on C - C*
how is light polarised?
by passing it through a polaroid filter, so oscillations are only in one plane
what effect does a racemic mixture have on plane polarised light?
none - the rotation by each enantiomer cancels out to nothing
what effect do the + and - isomers have on plane polarised light?
+ rotates plane clockwise
- rotates plane anti clockwise
what is the structure of a polarimeter?
light source (unpolarised light) –> polarising filter (polarised light) –> polarised light passes through compartment containing sample –> detector determines the angle of rotation of the plane polarised light
what are polarimeters used for?
to identify which enantiomer is present, the purify of the sample, the concentration of the sample etc.
are racemic mixtures formed in nature? why?
not often, as enzyme mechanisms are 3D so only form one enantiomer
why is optical isomerism a problem for the drug industry?
sometime, only one enantiomer is effective due to enzyme’s active site/cell receptors being 3D
what are the options to resolve the issue of only one enantiomer being effective?
1 separate enantiomers - difficult and expensive as have very similar properties
2 sell racemate - wasteful as half is inactive
3 design alternative synthesis to only produce one enantiomer
examples of optically active drugs?
ibuprofen, thalidomide
why is ibuprofen able to be sold as a racemate, even though the + isomer is needed to treat inflammation?
sold as 50% racemate
but body converts 60% of R- isomer to S+ isomer –> end up with 80% S+ isomer
what is the carbonyl group?
C=O
what is the functional group of an aldehyde?
RCHO (C double bonded to O, single bond to H and R) C=O is on end of chain
-al
what is the functional group for a ketone?
RCOR’ (C double bonded to O) C=O in middle of chain
-one
what kind of intermolecular forces do molecules with the carbonyl group have? why?
permanent dipole-dipole due to the polar C=O bond (O is delta -) not hydrogen bonds
how soluble are carbonyl groups in water? what influences solubility?
yes - form hydrogen bonds between water molecules and oxygen of C=O
as C chain length increases, solubility decreases
which bond in carbonyl compounds is usually involved in reactions? why?
C=O due to the polarity of the bond (large difference in electronegativity between C and O)
C=O is also the strongest bond in carbonyl compounds
why is adding HCN useful for carbonyl compounds?
increases the length of the carbon chain by one carbon atom - very useful!
will the product of HCN added to a carbonyl compound have optical isomers? why?
yes they will
in the aldehyde/ketone, the carbonyl carbon is planar, so the CN- can attack from either above or below forming two enantiomers
what is the name of the product when HCN is added to a carbonyl compound?
hydroxynitriles (have OH and CN groups)
what is Fehling’s solution? what colour is it?
copper complex ions
blue
what happens when an aldehyde is added to Fehling’s solution?
reduced to Cu+ ions –> colour change to brick red ppt
no change when a ketone is added
what is in Tollens’ reagent? what colour is it?
silver complex ions
colourless solution
what happens when an aldehyde is added to Tollens’ reagent?
silver mirror forms as Ag+ reduced to Ag(s)
ketone - no visible change
what is a quantitative test for the presence of a carbonyl group and how do you identify the carbonyl compound?
2,4-DNP reacts with both aldehydes and ketones to form an orange precipitate
to identify the compound take the melting point of orange crystal product and compare with known database values
reaction of propanone with iodine in the presence of alkali
CH3COCH3 + 3I2 + 4NaOH –> CHI3 + CH3COONa + 3NaI + 3H2O
what is another oxidising agent for alcohols and aldehydes? what change in colour does this undergo?
acidified potassium dichromate (VI) - H2SO4 and K2Cr2O7
colour change from orange to green
what is a reducing agent for aldehydes and ketones? what ions does this release in solution?
NaBH4 (sodium tetrahydridoborate (III)) or lithium tetrahydridoaluminate releases an H- ion
what type of mechanism is the reduction of an aldehyde?
nucleophilic addition
what is the functional group for a carboxylic acid?
-COOH
-oic acid
are carboxylic acids soluble in water? why? what influences their solubility?
yes - acid group can form hydrogen bonds with water molecules
what are the intermolecular forces in carboxylic acids?
hydrogen bonds in solid state - very strong
what are the 3 ways to prepare carboxylic acid?
oxidation of alcohols or aldehydes
hydrolysis of nitriles
propanoic acid and lithium tetrahydridoaluminate equation
CH3CH2COOH + 4[H] –> CH3CH2CH2OH + H2O
ethanoic acid and phosphorus (V) chloride equation
CH3CH2COOH + PCl5 –> CH3CH2COCl + POCl3 + HCl
how are esters formed? what is their functional group?
formed from carboxylic acids and alcohols
RCOOR’ (C=O, C-O-C)
ethanoic acid and propan-1-ol equation
CH3COOH + CH3CH2CH2OH –> CH3COOCH2CH3 +H2O
how do you name esters?
start with the group that has replaced the hydrogen then acid
e.g. propyl (from alcohol) ethanoate (from carboxylic acid)
equation for equilibrium formed by ethanoic acid in solution
(what happens to the - charge on the ethanoate ion in terms of electrons?)
(just an acid base question, HA —> ?)
CH3COOH(aq) ⇌ CH3COO-(aq) + H+(aq)
electrons delocalise so the - charge is shared across the whole of the carboxylate group
how can you distinguish carboxylic acids from other -OH containing compounds?
add NaHCO3, acids will produce sodium salt, water and carbon dioxide
ethanoic acid with NaOH equation
CH3COOH + NaOH –> H2O + CH3COO-Na+
ethanoic acid and Na2CO3 equation
2CH3COOH + Na2CO3 –> 2CH3COO-Na+ + H2O + CO2
what catalyst is needed for the formation of esters from alcohols and carboxylic acids?
conc strong acid e.g. H2SO4
what catalyst is needed for the hydrolysis of esters?
dilute strong acid e.g. H2SO4
what is an alternative method of hydrolysis? advantages?
base hydrolysis
reaction goes to completion due to neutralisation by base - more product in the mixture than acid catalysed hydrolysis
acid hydrolysis of ethyl propanoate equation and conditions
CH3CH2CCO2CH2CH3 + H2O ⇌ CH3CH2CO2H + Ch3CH2OH
dilute acid and heat under reflux
base hydrolysis of ethyl propanoate equation and conditions
CH3CH2CO2CH2CH3 + NaOH –> CH3CH2CO2-Na+ + CH3CH2OH
heat under reflux
what is transesterification?
converting one type of ester to another
what are carboxylic acid derivatives?
molecules that have the acyl group (R-C=O) as part of their structure, formed from carboxylic acids
e.g. acyl chlorides RCOCl, acid anhydrides RCOOCR
for the acylation of acyl chlorides or acid anhydrides with ammonia as the nucleophile, what are the products?
an amide
ethanoyl chloride and ammonia equation
CH3COCl + 2NH3 –> CH3CONH2 + NH4Cl
what are the products of the acylation of acyl chlorides or acid anhydrides if the nucleophile is a primary amine?
N-substituted amide
ethanoyl chloride and methylamine equation
CH3COCl + CH3NH2 –> CH3CONHCH3 + CH3NH3Cl
what are the products of the acylation of acyl chlorides or acid anhydrides if the nucleophile is an alcohol?
an ester
ethanoyl chloride and ethanol equation
CH3COCl + CH3CH2OH –> CH3COOCH2CH3 + HCl
what are the products of the acylation of acyl chlorides or acid anhydrides if the nucleophile is water? what is the name of the reaction?
carboxylic acid (hydrolyses ester linkage)
hydrolysis
ethanoyl chloride and water equation
CH3COCl + H2O –> CH3COOH + HCl
what is a commercially important acylation reaction?
the manufacture of aspirin
condensation
small molecule eliminated (usually H2O) to form a larger molecule
how many monomers are condensation polymers usually formed from? what properties do the monomers have?
two
each have two functional groups
examples of condensation polymers?
polyesters, polyamides, polypeptides
what is the linkage in a polyester?
ester linkage RCOOR’
what molecule is eliminated in formation of a polyester?
H2O
what are the two monomers which form a polyester?
diol and dicarboxylic acid
or a molecule with both alcohol and a carboxylic acid functional groups
which monomers is terylene made from? what is it used for?
benzene-1,4-dicarboxylicacid
ethane-1,2-diol
a fibre for making clothes
why can condensation polymers be broken down? how are they broken down?
they have polar bonds
hydrolysis (opposite of condensation)
what is the difference between addition and condensation polymerisation?
condensation makes the polymer and eliminates a small molecule
addition polymerisation breaks C=C to form only one product (just the polymer)
why do polyesters not show hydrogen bonding?
all O-H bonds are removed during polymerisation
