Polar Aprotic Solvents

F- > Cl- > Br- > I-

Nucleophilicity = Basicity

Solvates cations

Polar Protic Solvents

I- > Br- > Cl- > F-

Nucleophilicity /=/ Basicity

Solvates cations and anions

SN1 Reactions

- formation of a carbocation

- love polar protic solvents

- result in EQUAL mixture of stereoismers (R and S) racemic mixture

- 3 > 2 > 1 > CH3 (1 and CH3 do not do SN1 reactions)

SN1 Reaction Rate

only the concentration of the alkyl halide affects the reaction rate

rate = [alkyl halide]

SN2 Reactions

- backattack

- love polar aprotic solvents

- can result in inversion of configuration if reaction is on a chiral carbon (if not, config. is retained)

- CH3 > 1 > 2 > 3 (3 does not undergo SN2)

E1 and E2 Reaction

3 > 2 > 1

SN2 Reaction Rate

concentration of alkyl halide and nucleophile affects reaction rate

[alkyl halide][Nu]

Examples of polar protic solvents

H20, MeoH, EtOH, acetic acid, ammonia

(contains a Hydrogen)

Examples of polar aprotic solvents

DMSO, DMF, acetone, acetonitrile, CN-, I-

Elimination is favored when

- using a strong base (pka > 14) and has a negative charge

- high temperature

- 2 or 3 alkyl halide

- using a strong, bulky base such as isopropyide or tert-butoxide

Zaitsev's Rule

formation of the most substituted alkene is favored with a small base

this is because the most substituted alkene is the most stable

most stable -> major product

E2 reactions on cyclic molecules

must be anti-coplanar

Cis formations on cyclic molecules yield how many products

2

Trans formations on cyclic molecules yield how many products

1

True/False

Trans alkenes are more stable than cis alkenes

True

when 2 alkenes can be formed, the most substituted will predominate when...

a strong unhindered base is used

when 2 alkenes can be formed, the least substituted will predominate when...

a strong, bulky base is used

when substituents are all facing up, the molecule is...

cis

when one substituent is facing up and the other is facing down, the molecule is...

trans

the halogen must be _____ in order to react with a labile hydrogen.

anti-coplanar

What kind of reagent would you use to eliminate a halogen?

A strong, bulky base

Basicity is a ____ matter

thermodynamic

Nucleophilicity is a _____ matter

kinetics

Regioselectivity

When more than one constitutional isomer is produced and one predominates

Stereoselectivity

When more than one stereoisomer is produced and one predominates

E ( entegegen)

when heaviest groups are on opposite sides of the plane

(based on atomic weight)

Z (Zusamenn)

when heaviest groups are on the same side of the plane

(atomic weight)

the most substituted has the ...

lowest heat of hydrogenation