Topic 6: Nucleophilic Substitution Flashcards
What happens when a single enantiomer of a primary alkyl halide reacts with a nucleophile
1 bond broken and 1 bond formed in synchronous fashion
Nucleophile attacks from behind the bond that is breaking
Inversion of configuration
SN2
The products when a single enantiomer of a tertiary alkyl halide reacts with a nucleophile are … . … step mechanism with a … intermediate. … can attack intermediate … by …
racemic
2
positively charged achiral trigonal planar
Nucleophile
above or below
SN1
Why would a nucleophile attack from behind?
Electrostatics: like charges repel so nucleophile approaches as far as possible from electron rich leaving group, minimising repulsive interaction
Sterics: nucleophile and leaving group on different trajectories so they don’t get in the way of each other
Stereoelectronics: donation of electron pair from nucleophile to electrophile from filled orbital in nucleophile (HOMO) to unfilled oribital in electrophile (LUMO)
HOMO and LUMO
Highest/lowest occupied MO
Do secondary alkyl electrophile react via a 1 or 2 step mechanism
Depends
What does SN2 mean
Substitution
Nucleophilic
RDS is bimolecular- 2 molecules involved (nucleophilic + electrophile)
SN2 transition states
Bonds breaking and forming have dotted lines as they haven’t completely formed or broken
Enclosed with square brackets with double dagger sign and overall charge in top right hand corner
What does SN1 mean
Substitution
Nucleophilic
RDS unimolecular depending on electrophile
SN1 transition states
2:
1st bond breaking have dotted lines as they haven’t completely broken
Enclosed with square brackets with double dagger sign in top right hand corner
2nd is the same but with dotted lines for bond being formed
Intermediate between 2 transition states
SN1 reaction solvents
Polar protic
E.g. alcohols and carboxylic acids
SN2 reaction solvents
Polar aprotic
E.g. DMF, HC, acetone, MeCN, DMSO
