SN2

What is SN2

Substitution, nucleohilie, biomolecular.

A nucleophile attaches to an electrophile and kicks out a leaving group

BAD Nu:

H2O, carboxylic acid, alcohols and anything with a t-butyl groups

Requirement for SN2 reactions

Carbon attached to LG needs to be sp³

What happens when a nucleophile attaches to an electrophile during SN2

Inversion of stereochemistry, the molecule flips 180 and so wedges and dashes switch.

I Bring Cookies, H2O, and Sweets!

I−>Br−>Cl−>H2​O>RSO3−​

what is OTS

A for RSO3- => a good LG

Fastest degree of substitution

methyl > 1 > 2 > 3

Beta branching

How many carbons are attached to the beta carbon

Leaving group ability and acidity

Conjugates of strongest acids are the best leaving groups

Periodic trends for Leaving gropus

To the right and bottom

Formal Charge of LG

The charge of the LG before leaving
+ > neutral > -

Resonance on LG

If the LG can do resonance then it is more stable when it leaves

Can you do an SN2 reaction with an alcohol?

OH is not a good leaving group to do SN2

OLD school method

Converting a primary OH into a good LG by using a H-X where x is a nucleophilic halogen. Only works with primary alcohols

What are good Nu: for converting

H-Cl, H-Br, and H-I

High Tech method

Replace OH with OTS. Works with primary and secondary alcohol

Periodic trends of Nucleophilic

To the left and bottom

Formal Charge of Nucleophiles

- > neutral > +

Sterics of nucleophiles

Bulkier nucleophiles are not good

Solvents affect on SN2

Polar aprotic solvents work best for SN2 reactions. Polar solvents stabilize polar transition of SN2 and Nu: are polar. Aprotic solvents are less reactive to the nucleophile because the lack of H bonding.

Polar aprotic solvents

Acetone, DMSO, DMF, HMPAA

Aprotic solvent

Does not have 1 H attached to an e- atom