[11.5] introduction to reaction mechanisms Flashcards
what are the two ways in which covalent bond can be broken?
- homolytic fission
- heterolytic fission
what occurs when a covalent bond is broken by homolytic fission?
- each of the bonded atoms each takes one of the shared pair of electrons from the bond
- each atom now has a single unpaired electron
what is a radical?
an atom or groups of atoms with an unpaired electron
(example) homolytic fission of the carbon-carbon bond in ethane
H₃C-CH₃ -> H₃C●+ ●CH₃ (radicals)
what occurs when a covalent bond is broken by heterolytic fission?
- one of the bonded atoms takes both of the electrons from the bond
- the atom that takes both electrons becomes a negative ion
- the atom that does not take the electrons becomes a positive ion
(example) heterolyic fission of the carbon-chlorine bond in chloromethane
H₃C-Cl -> H₃C⁺ + Cl⁻ (ions)
what is reaction mechanism?
the process of providing information about how a reaction takes place
what do curly arrows show in reaction mechanism?
they show the movement of electron pairs when bonds are being broken or made
where must curly arrow start?
- from a lone pair of electrons
- from a charge
- or, when showing bond breaking, from the middle of the line (C–Cl)
curly arrows and homolytic fissions
fish-hook arrows (arrows with half an arrow head) represent the movement of a single, unpaired electrons in mechanisms involving radicals (ie. homolytic fission)
what are the 3 types of reaction?
- addition
- substitution
- elimination
what is an addition reaction?
when two reactants join together to form one product
what is a substitution reaction?
when an atom or group of atoms is replaced by a different atom or group of atoms
what is an elimination reaction?
when a small molecule is removed from a larger one (eg. water)
- one reactant molecule forms two products
