o chem– alkenes Flashcards
what are 2 other names for LDF attractions?
- id-id
- VDW’s forces
do cis isomers or trans isomers have higher boiling points?
cis isomers
why do cis isomers have a higher b.p.? (4)
- cis isomer has net dipole moment
- trans does not -> individual dipole moments cancel out
- thus cis is a polar molecule
- held together by pd-pd attractions which are stronger than id-id attractions btw non-polar trans isomer
- more energy needed to overcome pd-pd attractions
- thus higher b.p
does cis or trans isomer have a higher m.p.?
trans
why does the trans isomer have a higher m.p.? (4)
- better symmetry than cis isomer
- allows more efficient packing of solid
- closer packing allows for stronger id-id attractions btw molecules
- more energy req to overcome
- thus higher m.p.
electrophiles are electron ________ species
deficient
why do alkenes undergo reactions with electrophiles
- alkenes are e- rich due to presence of 2π e- in double bond
- electrophiles (e- deficient) are attracted
what are the reagents and conditions of electrophilic addition with HX?
r.t., HX
write out the mechanism for the addition of HBr to C2H4
-
what is markonikov’s rule?
the electrophile is added to a C=C double bond in a way such that the most stable carbocation intermediate is produced
what does markonikov’s rule mean for the
the electrophile (delta +) is added to the C atom in the C=C that has the most no. of H
the most stable carbocations are…
tertiary carbocations
why are tertiary carbocations the most stable (similar concept to tertiary radicals) (2)
- has the greatest number of e- donating alkyl groups
- positive charge of the carbocation is dispersed to a larger extent
what is a racemic mixture?
a mixture of an equal amount of 2 enantiomers
why is a racemic mixture formed?
- nucleophile attacks a trigonal planar carbocation
- nucleophile has equal chance of attacking from either side of the plane
- thus equal amts of enan formed
