alkenes Flashcards
why is there no rotation around the C=C double bond?
due to pi orbital
electron density above + below single bond
holds the C atoms in place
why are alkenes more reactive than alkanes?
higher electron density of double bond
pi bond is easier to break
what IM forces of attraction do alkenes have?
only vdW due to non-polar bonds
why are alkenes not soluble in water?
non polar bonds
van der waals are weaker than H bonding
what is an electrophile?
electron deficient atom/ion
accept a pair of electrons
(from the c=c bond)
what is the most stable kind of carbocation intermediate?
alkyl groups
have positive inductive effect
so most stable carbocation is the one BONDED TO MOST OTHER C ATOMS
(tertiary)
major products will be formed from which type of carbocations?
tertiary
(or most stable available?
conditions needed for electrophilic addition of H2O to an alkene?
acid catalyst
phosphoric acid usually
conditions needed for electrophilic addition of a hydrogen halide to an alkene?
room temperature
conditions needed for electrophilic addition of halogen molecule to an alkene?
room temperature
organic solvent
how does a non polar molecule act as if it were an electrophile?
C=C has high electron density
induces a temporary dipole in halogen molecule
partially positive atom attracted to double bond
3 uses of poly(chloroethene) / PVC
drainpipes
vinyl
aprons
why do things containing mainly c-c and c-h bonds not decompose easily?
bonds are non polar
so not attacked by enzymes
what are stereoisomers?
molecules with same structural formula
BUT
different spatial arrangement of atoms/gps
what type of bond is the C=C bond?
planar bond
what is addition polymerisation?
reaction by which alkenes react with another alkene to form polymers
why are addition polymers unreactive?
lack reaction C=C bond
this is an area of high electron density
and vulnerable to electrophilic attack
forces between polymer molecules?
weak vdW forces
why do some polymers melt over a range of temperatures?
consist of chains of different lengths
varying strength of vdW
why are the IM forces between polymers often strong?
chains often long
many electrons
many vdW
why does a tertiary carbocation form the major product?
tertiary carbocation has more alkyl gps attached POSITIVE INDUCTIVE EFFECT reduce + charge on carbon MORE STABLE remains in reaction mixture longer so MORE LIKELY TO REACT WITH ELECTROPHILE
what is an electrophile?
electron pair acceptor
what is a carbocation?
species containing positive charge on C atom
is dilute sulphuric acid an electrophile?
NO
concentrated sulphuric acid is an electrophile
what is heterolytic fission?
covalent bond breaks and both electrons move to one atom
2 OPPOSITELY CHARGED IONS FORMED
