Reaction mechanisms Flashcards
What are the 4 types of organic reactions and what are they?
1. Substitution: An atom (group) of the moleucle is replaced by another atom (group)
2. Addition: π bond of a compound serves to create two new covalent bond that join two reactant together
3. Elimination: Two atoms (groups) are removed from a moleucle which is thus cleft into two products
4. Rearragement: Atoms and bonds are rearranged within the molecule; this, isomeric compound is formed
Whats mean by the following:
- Homolytic mechanism
- Heterolytic mechanism
Homolytic mechanism: each fragment possesses one of the bonding electrons; thus, radicals are formed
A-B –> A• + B•
Heterolytic mechanism: One of the fragments retain both of the bonding electrons, thus ions are formed
A-B –> A+ + :B-
Whats homogenic bond making?
one electron donated by each fragment (radical)
Whats heterogenic bond making?
Two electrons donated by one frament
Give two examples of nucleophiles and electrophiles?
Nucleophiles:
- Anions (H-, OH-)
- Neutral molecules (NH3, HOH)
Electrophiles:
- Cations
- Neutral molecules (lewis acids: AlCl3)
Whats nucleophilic substitution and whats the general formula?
What type of compound tends to react in this way?
An electron-rich nucleophile introduces an electron pair into the substrate; the leaving atom/group retains the original bonding electron pair
:Nu- + R-Y –> Nu-R + :Y-
This reaction is typical of haloalkanes
Whats are the two type of nucleophilic substitution reactions?
SN2 and SN1
Whats the SN2 reaction?
- takes place in a single step without intermediates
- Bimolecular reaction
- incoming nucleophile reacts with the alkyl halide or the substrate from a rdirection opposite the group that is displaced (the leaving group)
Whats the rate equation for the SN2 reaction and whats its steroechemical outcome?
Rate equation:
rate = k[R-Hal][Nu]
stereochemical outcome:
inversion
Whats the rate equation for the SN1 reaction and the stereochemical outcome?
Rate equation:
rate = k[R-Hal]
Stereochemical outcome:
Racemisation
Tell me some facts about SN1 reactions?
- unimolecular
- Has two step, first step is the rate-determining step
Look up mechanisms for SN1 and SN2 reactions
Whats an electrophilic addition reaction and whats it typical of?
An electrophile forms a covalent bond by attacking an electron-rich unsaturated C=C bond
Typical of: alkenes and alkynes
Whats the mechanism for nucleophilic addition reactions?
What are the 3 elimination mechanisms? What are they?
1. E1 mechanims: two step, unimolecular reaction mechanim involving carbocation intermediate, step wise action
2. E2 mechanisms: One step, bimolecular reaction mechanism, concerted action
3. E1cB mechanim: two step mechanisms involved carbanion intermediate; step wise action
Whats Keto-enol tautomerism?
An equilibrium between a keto and an enol form of carbonyl compounds
