alkenes Flashcards
positive inductive effect definition
the ability to release electron density through a covalent bond
why are tertiary carbocations more stable than secondary carbocations
there is a positive inductive effect from 3 alkyl groups in a tertiary carbocation compared to 2 alkyl groups in a secondary carbocation
electrophile definition
an electron pair acceptor
what is an alkenes shape and bond angle
shape = planar
angle = 120*
which bond out of sigma and pi is more reactive and stronger
- a sigma bond is stronger as it has a higher bond enthalpy (347) than the pi bond (265)
- the pi bond is more reactive as less energy is needed to break the bonds
orbital definition and their shapes
a region of space where up to 2 electrons can be found
why is there no rotation around C=C bonds
- pi bond formed by overlap of p orbitals
- if rotation did occur, p orbitals would not overlap and pi bond would break
electrophilic addition with hydrogen halides:
reagent, conditions, product, electrophile, why it is an addition reaction mechanism and overall reaction
reagent = HBr or HCl
conditions = none
product = haloalkane
addition reaction = H atom and Br atom have been added
electrophile = H-Br
overall= CH2=CH2 + HBr -> CH3CH2Br
why is 2-bromopropane the major product
- 2-bromopropane is made from a secondary carbocation
- 1-bromopropane is made from a primary carbocation
- secondary carbocations are more stable than primary carbocations due to the positive inductive effect of the two alkyl groups
electrophilic addition with halogens
reagent, conditions, product, mechanism, overall reaction
reagent = Cl2 or Br2
conditions= none
product= haloalkane
overall reaction=
CH2=CH2 + Br2 —> CH2BrCH2Br
mechanism=
explain why bromine molecules react with the double bonds in alkenes
- C=C bond is electron rich
- this induces a dipole in Br2
- partially positive Br is attracted to C=C double bond
chemical test for alkenes
reagent, observations, overall equation
reagent = Br2 (orange liquid)
positive result = orange to colourless (alkenes present)
negative result = no visible change (alkenes not present)
overall= CH2=CH2 + Br2 —> CH2BrCH2Br
electrophilic addition with sulphuric acid
reagent, conditions, product, mechanism, overall reaction
reagent= H2SO4
conditions= none
product= alkyl hydrogen sulphate
overall= CH2=CH2 + H2SO4 —> CH3CH2OSO3H
mechanism=
(ignore H2O)
how to make alcohols from alkenes
step 1 =
alkene + H2SO4 —> alkyl hydrogen sulphate
step 2=
alkyl hydrogen sulphate + H2O —> alcohol + H2SO4
role of H2SO4 in making an alcohol into an alkene
Catalyst
-as H2SO4 is reproduced
electrophilic addition - direct hydration
reagent, conditions, product
reagent = H2O (g)
conditions = concentrated H3PO4 catalyst
product = alcohol
