5. Alkenes Flashcards
general formula
CnH2n
what does a C=C consist of
one sigma bond
one pi bond
Why are pi bonds vulnerable to electrophiles
they have a high density
how is a sigma bond formed in a C=C
one sp2 orbital from each carbon overlap to form a single C-C
how is pie bond formed in C=C
- sideways overlap with 2 p orbitals
- forms a pie bond above and below the plane of molecule
which bond is weaker: pie or sigma
Pie bond
sterioisomers
same structural formulae but different spatial arrangement of atoms
why do E-Z isomers exist
due to restricted rotation about the C=C
when do E-Z isomers arise
- restricted rotation around the C=C
- two different groups/atoms attached to the double bond
cis isomers
same side
Trans isomers
different sides
Alkenes with hydrogen
- alkene-> alkane
- reagent: hydrogen
- condition: nickel catalyst
- type of reaction: addition
electrophile
electron pair acceptor
reactions with halogens
- reagent: bromine
- condition: rtp
mechanism of reaction of alkenes with halogens + type of bond fission
electrophillic addition
heterolytic
test for alkenes
bromine water (orange) decolourises
Reaction with steam
reagent: H2 gas
condition:
concentrated phosphoric acid
pressure (60-70)
temperature (300c)
alkenes with potassium manganate and H+
- forms diols
- observation : KMnO4 solution turns colourless from purple
boiling point
increases with molecular mass
lower than alkanes
solubility
insoluble in water but soluble in organic solvents
