isomerism
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define structural isomers
compounds that have the same molecular formula but different structural formula.
what are chain structural isomers
structural isomers which have different arrangements of the carbon skeleton
properties of chain structural isomers
similar chemical properties different physical properties (more branching results in lower boiling point)
what are positional structural isomers
structural isomers which have the same functional group but the functional group is in a different position on the carbon skeleton.
properties of positional structural isomers
similar chemical properties slightly different physical properties
what is a functional group structural isomer
structural isomers which have different functional groups
properties of functional group structural isomers
different chemical properties different physical properties
define stereoisomerism
same molecular formula same bonds present different 3 dimensional orientation of their atoms in space
Z
same side
E
different side
what two characteristics does a molecule need to show geometric isomerism
double bond the two groups on the carbons of the double bond should be different (both carbons can have the same two groups as long as the 2 differ from each other)
what is geometric isomerism
occurs around double bonds restricted rotation around the double bond molecules do not readily interconvert
define optical isomers
are molecules which are isomers which are non superimposable mirror images of each other
what is a chiral carbon
a carbon with 4 different groups attached to it (often means a molecule shows optical isomerism)
what key property do optical isomers show regarding plane polarised light
optical isomers rotate the plane of plane polarised light each isomer will rotate the light by the same amount but in the opposite direction
what is a racemic mixture
a solution which contains equal numbers of moles of both optically active isomers/enantiomers of a compound
why are racemic mixtures not optically active
optical rotations will cancel out
which nuleophillic substitution mechanism do tertiary halogenoalkanes react via
SN1
which nucleophillic substitution mechanism do primary halogenoalkanes react via
SN2
what is steric hindrance
large groups getting in the way of attacking species
do primary or tertiary halogenoalkanes have a lower steric hindrance (and therefore lower stability)
primary
why does SN2 mechanism mean optical activity
SN2 can only be attacked from 1 angle (opposite side of leaving group) all molecules form bonds in the same place pure therefore shows optical activity
why does SN1 mechanism mean no optical activity
can be attacked from various places bonds can form in various places forms a racemic mixture of the 2 isomers optical activity of each isomer cancels out so none shown