topic 6C Flashcards
general formula for alkenes
CnH2n
bonding in alkenes
- C=C double covalent bond consists of one sigma and one pi bond
- pi bonds are exposed and have higher electron density
formation of sigma (σ) bond
- one sp2 orbital from each carbon overlap to form a single C-C bond (σ)
formation of pi (π) bond
- bond is formed by sideways overlap of two p orbitals on each carbon atom forming a π bond above and below the plane of the molecule
- restricted rotation about pi bond
what is an electrophile
an electron pair acceptor
reaction of alkenes with hydrogen
- group change
- reagent
- conditions
- type of reaction
- group change: alkene to alkane
- reagent: hydrogen
- conditions: nickel catalyst
- type of reaction : addition/reduction
electrophilic addition: reaction of alkenes
- sigma bond is weaker than a pi bond so less energy is needed to break a sigma bond.
- the bonds in alkenes are areas with high electron density.
- this is accesible to electrophilic attack by electrophiles
- alkenes udnergo addition reactions
reaction of alkenes with bromine/chlorine
- group change
- reagent
- conditions
- mechanism
- type of reagent
- type of bond fission
- group change : alkene to dihalogenoalkane
- reagent : bromine dissolved in organic solvent
- conditions : room temp
- mechanism : electrophilic addition
- type of reagent: electrophile
- type of bond fission : heterolytic
reaction of alkenes with hydrogen bromide
- group change
- reagent
- conditions
- type of reaction
- group change : alkene to halogenoalkane
- reagent: HCl or HBr
- conditions: room temp
- mechanism: electrophilic addition
- reagent type: electrophile
- bond fission: heterolytic
reaction of alkenes with potassium manganate (VII)
- group change
- reagent
- conditions
- type of reaction
- observation
- group change: alkene to diol
- reagent: KMnO4 in acidified solution
- conditions: room temp
- type of reaction: oxidation
- observation: purple to colourless
reaction of alkenes with bromine water
- reagent
- conditions
- type of reaction
- observation
- reagent: bromine dissolved in water
- conditions: room temp
- type of reaction: addition
- observation: orange to colourless
hydration of alkenes to form alcohols
- reacted in water in the presence of an acid catalyst
essential conditions for the hydration of alkenes
- high temperature 300 to 600°C
- high pressure 70 atm
- catalyst of conc H3PO4
what do high pressures mean
- it cannot be done in the lab; must be done industrially
- there are no waste products so there’s a high atom economy
- separation of products is easier and cheaper
what is heterolytic bond fission
heterolytic bond fission of a covalent bond results in the formation of ions