2.1 stereochemistry Flashcards
in a biological system, what usually occurs with optical isomers?
usually, only one isomer will be present in the system and be biologically active. the other isomer will be biologically inactive or cause a different response.
optical isomers have identical chemical properties except:
when in a chiral environment, e.g. a biological system
what is the name given to a mixture containing equal amounts of both optical isomers?
a racemic mixture
why are racemic mixtures optically inactive?
the rotational effect of one enantiomer will cancel out the other
what can be said of mixtures containing equal amounts of both optical isomers
they will be optically inactive (have no effect on plane polarised light)
what can be said of substances that rotate plane polarised light?
that they are optically active
how is plane polarised light rotated by each enantiomer?
one will rotate it in a clockwise direction, the other in an anticlockwise direction. the light will be rotated by the same amount
optical isomers have identical physical properties, except for:
their effect on plane polarised light
define optical isomers
non-superimposable mirror images of each other (called enantiomers)
how many isomeric forms can an atom containing a chiral carbon have?
two
what is a chiral carbon?
a carbon that has four different groups attached
where does optical isomerism occur?
when a molecule contains a chiral carbon
why can geometric isomerism also arise in cyclic structures?
ring structure means that rotation around the C - C bond becomes restricted.
why are trans isomers usually less polar than cis isomers?
symmetry allows polarity to cancel out
which type of geometric isomer is usually more polar?
cis
which type of geometric isomer usually has a higher boiling point?
cis
when do cis isomers occur?
when the groups are on the same side of the double bond
when do trans isomers occur?
when the groups are on the opposite side of the double bond
why does geometric isomerism occur?
as there is no free rotation of the groups of atoms around a double bond
where does geometric isomerism occur?
in molecules containing a C = C bond, when there are different groups on each side of the double bond
when do stereoisomers occur?
when atoms are bonded together in the same order but are arranged differently in a 3D space
when do structural isomers occur?
when atoms are bonded together in a different order
