paper 2 practise Flashcards
what is meant by a sigma bond?
the head on overlap of p-orbitals between carbon atoms
what is meant by a pi bond?
the sideways overlap of p-orbitals above/below the carbon atoms
how do you determine the number of pi/sigma bonds?
pi=no. of double bonds
sigma=all bonds C-C,C-H etc.
why can some compounds not show stereoisomerism?
one of the carbons in the C=C could have two of the same groups attached
what is one way of determining the number of optical stereoisomers?
number of chiral centres (cis sometimes) double it
how can you recrystallise the impure crystals to obtain a pure sample of C?
- dissolve the crystals in hot solvent
- add the minimum amount of solvent
- cool it,filter it and leave it to dry
why could an unsaturated hydrocarbon have a lower melting point?
more branched=fewer points of contact
fewer points of contact=weaker induced dipole-dipole interactions so less energy required to overcome the intermolecular forces
how can you check the purity of the compound?
- obtain the melting point and compare to known values
- a pure sample will have a sharp melting point very close to the data book value
state the trend in the relative ease of nitration of phenol,benzene and benzoic acid
phenol is more easily nitrated
why is phenol more easily nitrated compared to benzene/benzoic acid?
- phenol has a lone pair of electrons on a benzene ring so delocalises into the ring
- as a result the ring is more susceptible to attack
- COOH group on the benzoic acid is an electron withdrawing group
why could a polymer be biodegradable? (but only if an ester)
ester group can be hydrolysed
what can make an alcohol more soluble?
if it contains more OH groups.
what statements are true about recrystallisation?
the organic compound is more soluble in hot solvent AND the hot solution is cooled before the purified organic compound is collected
why can/can’t 13C NMR spectroscopy be used to distinguish compounds?
can=different number of carbon environments
can’t=if it contains OH/NH and D2O is added they may be the same so hard to distinguish
name two ways you can identify a carbonyl group and distinguish between two compounds without using spectroscopy
- Brady’s reagant=orange crystalline precipitate
- measure melting point and compare it to known values
