o chem– alkenes
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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
the conditions for electrophilic addition of alkenes with a gas X2 is… 1. X2 2. r.t.p. 3. _______________
absence of UV light
how is alcohols produced from alkenes?
water is added
what are the reagents for lab synthesis of alcohol from alkenes?
• cold conc H2SO4 • warm H2O
the industrial method for alcohol production from alkenes is…
steam, H3PO4 catalyst, 300ºC, 65 atm
what kind of reaction is the addition of H2 to alkenes?
reduction/hydrogenation
how are alkanes produced from alkenes?
addition of H2 (g)
the reagents and conditions of hydrogenation are… 1. H2 (g) 2. ??? catalyst 3. high T and P
Ni
what catalyses addition polymerisation? (short)
radicals, salts
what are the conditions for add polym?
high pressure