Mechanisms Flashcards
Outline the 3 parts of free radical substitution
Initiation
Propagation
Termination
What atoms are involved in free radical substitution?
Halogen atoms
Outline the steps in initiation
Diatomic atoms gain one electron each to become 2 free radicals
e.g: Cl2 -> 2Cl*
Outline the steps in propagation
- One free radical reacts with reagent to form a new free radical from the compound
- New free radical reacts with diatomic atoms to form OG free radical
Outline the propagation of CH3CH2F + Cl2
- CH3CH2F + Cl* -> CH3C*HF +HCl
- CH3C* HF +Cl2 -> CH3CHFCl + Cl*
Outline the steps of termination
All 3 combinations of free radicals cancel out
Outline the 3 termination steps for CH3CH2F + Cl2
- Cl* + Cl* -> Cl2
- CH3C* HF + Cl* -> CH3CHClF
- 2CH3C*HF -> CH3CHF - CHFCH3
Outline the 3 Nucleophiles, their reagents and the conditions that undergo nucleophilic substitution
- :OH- - KOH/NaOH (aq) - Reflux
- :CN- - NaCN/KCN (aq) ethanol solvent - Reflux
- :NH3 - NH3 - sealed tube
Outline why Ammonia nucleophilic substitution is in a sealed tube
NH3 BP is low so reflux = evaporate
Outline the mechanism steps for nucleophilic substitution with ammonia
- NH3 bonds to C with Halogen - removes halogen atom
- CNH3+ loses H atom from 2nd :NH3 atom to form NH4+
- NH4+ forms NH4Br with :Br-
Outline what atoms react in elimination
Halogenoalkane + KOH or H2SO4
Solvent = ethanol
Outline the steps of elimination reactions
- :OH- bonds with H on adjacent C to C with halogen - creates double bond & H2O
- Halogen lost by saturated C - alkene formed
Outline the 2 reactions of how CFCs reduce Ozone
- Cl* + O3 -> ClO* + O2
- ClO* + O3 -> Cl* + 2O2
Define electrophiles
Electron pair acceptor
Outline what reacts in electrophilic addition
Alkenes (or anything e- dense) and electrophiles
Outline 3 electrophiles
- Halogens (Br2, Cl2, etc)
- HBr
- H2SO4 (used in fermentation)
Outline the steps in electrophilic addition
- Electrophile accepts e- (+ dipole gains)
- -ve Ion attacks + C atom
Outline the structure of H2SO4 when drawing mechanisms
H—OSO3H
Outline the electrophilic addition steps of fermentation
- H+ accepts 2e- from C=C
- :O-SO3H attacks C+ forming alkane
- Warm H2O with H+ (aq) used - forms alcohol from alkane & reforms H2SO4
Define a Carbocation
Ion with a + C atom
Outline primary, secondary and tertiary carbocations
Primary = Only attached to 1 C group
Secondary = Attached to 2 C groups
Tertiary = Attached to 3 C groups
Rank the 3 carbocation types by stability in descending order and outline why
Tertiary, Secondary, Primary
Tertiary most stable because alkyl group slightly release e- towards C+ (inductive e- donating)
What determines the major and minor product of electrophilic addition?
The C+ stability
More stable C+ = major product
Outline the 2 nucleophiles that react in nucleophilic addition
- :CN-
- :H-
What type of compound reacts in nucleophilic addition?
Ketone
Outline the 2 reagents that react in nucleophilic addition
- Acidified KCN (aq)
- NaBH4 (aq)
Why does the nucleophilic addition of ketones form racemic mixtures
Outline the mechanism steps of the nucleophilic addition between butanone and HCN
- :CN- ion attacks the +δ C atom part of the C=O group. e- pair attacks the =O group forming :O-
- The :O- ion attacks a H+ ion from the acid forming an R-OH group
Outline the mechanism steps of the nucleophilic addition of a ketone with 2[H]
- :H- ion attacks the +δ C atom bonded to the C=O group. The e- pair from C=O attacks the O atom forming :O-
- The :O- atom attacks a H+ ion forming an R-OH group
