isomerism Flashcards
why do alkenes have a restricted rotation about the double bond?
the pi bond is the overlap of the two p orbitals from each carbon. this is slightly above and slightly below the carbon atom rather than directly between them. rotating would remove the overlap and break the bond
what is E/Z isomerism?
It’s a type of stereoisomerism in which the groups attached to either side of the C=C bond can be arranged differently in space because of the restricted rotation around the C=C bond
why do alkenes express E/Z isomerism?
there is restricted rotation about the double bond.
how are the E and Z isomers determined
priority is assigned to each group attached to the carbons with the double bond based on atomic number. if the highest priority on the left and right carbons are parallel to the bond then it’s the Z isomer.
how do the physical properties of E and Z isomers differ?
Z isomers can be polar if one of the groups forms a polar bond with carbon. E isomers cant be polar if both of the groups form polar bonds with carbon. this causes a higher boiling point for Z isomers.
E isomers pack together more tightly so they have stronger induced dipole-dipole interactions so E isomers have higher melting points
whats cis/trans isomerism
when each carbon atom in the c=c bond have an identical group attached
what is a structural isomer?
compounds with the same molecular formula but different structural formulae. for example Butane(C4H10) and methylpropane (C4H10)
Branched structural isomers are also called chain isomers
why are alkenes and cycloalkanes isomers
they are functional group isomers because they can have the same molecular formula but a different functional group
why can alkenes have positional isomers?
the functional group can be in positions places along the chain indicated by the number in the name (e.g. But-1-ene or But-2-ene)
