Alkyl Hallides

Chapter 11

The larger the halogen, the _____ the carbon-halogen bond, and the _____ the bond length.

The larger the halogen, the weaker the carbon-halogen bond, and the larger the bond length.

Based on electronegativity, we expect the carbon of alkyl halides to be ______ polarized. Making the carbon the __________.

Based on electronegativity, we expect the carbon of alkyl halides to be positively polarized. Making the carbon the electrophile.

the higher the bond strength, ___________, and the more _____ the radical is

the higher the bond strength, the harder it is to rip apart, and the more unstable the radical is

radical stability (most stable to least stable)

• 3^o allylic/benzyllic

• 2^o allylic/benzyllic

• 1^o allylic/benzyllic

• 3^o

• 2^o

• 1^o

• acrylic/vinylic

radical substitution requires three steps:

1. initation

2. propogation

3. termination

how to make an alkyl halide

1. radical halogenation

2. allylic bromination (use NBS)

3. monohalogenation

4. dihologenation

5. alcohol

oxidation

decreases e- density on carbon by

• forming C-O, C-N, C-X

• breaking C-H

reduction

increasing e- density on carbon by

• forming C-H

• breaking C-O, C-N, C-X

radical halogenation

alkane (no double bonds) + light + Cl₂ or Br₂ = alkyl Hallie

Cl is not selective

Br is selective

in radical halogenation _____ is not selective, while ____ is selective

in radical halogenation Cl is not selective, while Br is selective

Br is less reactive (less electronegative) than Cl, and as a result only really reacts with the weakest C-H bond (tertairy), resulting in the most stable radical (tertiary radical)

allylic bromation

NBS+ alkene + light = alkyl halide with bromine at the allylic position

alcohol substitution

1. HCl, HBr, HI (not HF), can rip alcohols off of tertiary carbons

2. SOCl₂ and PBr₃ can rip alcohols off of primary and secondary carbons, they also flip the stereocenters

3. HF can rip alcohols off of primary and secondary carbons, but they are often combined with pyradine for safety reasons

when we start with an alkene we can use

• HBr (monohalogenation)

• Br₂ or Cl₂ (dihalogenation)

• NBS

formation of Grignard reagents $

formation of gilman reagents

organometalic coupling

we always pair HF with

pyridine

gringard reations occur in what solvents

ether, THF (weakly polor, aprotic solvent)