Ch 8

dehydration reaction

secondary or tertiary alcohols + acid (H2SO4) w THF solvent and heating → alkene + water

dehydration reaction arrows

process is reversible, so in excess, the water forces reaction back towards the alcohol (converts alkene into alcohol)

dehydration reaction intermediate

oxonium ion where H2O detaches and forms carbocation intermediate

dehydration reaction acids

uses weak acids, does not work well w H-X acids (those give substitution bc X ions are much more nucleophilic)

syn product in alkene reactions

product is synperiplanar

anti product in alkene reactions

product is antiperiplanar

syn stereochem in alkene reactions

during mechanism, both new bonds formed occur on the same face

anti stereochem in alkene reactions

during mechanism, both new bonds formed occur on the different faces

halohydrin

alkene + X2 and H2O → OH and X antiperiplanar alkane

halohydrin mechanism

anti addition and follows markovnikov’s rule

HX Reaction

• markovnivov product formed

• carbocation intermediate

• racemization occurs if new chiral center forms

X2 Reaction

• anti stereochemistry - anti periplanar groups

H2SO4 + H2O + heat →

• Markovnikov product formed

• carbocation intermediate

• ½ - acid catalyzed addition that forms an alcohol

• not stereoselective

• can have carbocation rearrangements

H3PO4 + H2O + heat →

• Markovnikov product formed

• carbocation intermediate

• 2/2 - acid catalyzed addition that forms an alcohol

• not stereoselective

• can have carbocation rearrangements

1. Hg(OAc)2, H2O/THF

2. NaBH4

• Markovnikov product formed

• hydration reaction

• no carbocation rearrangements

• hydration and addition that forms an alcohol

1. BH3, THF

2. H2O2, HO-

• addition leads to mix of two enantiomers

• anti-markovnikov product in asymmetric alkenes

• hydration and addition that forms an alcohol

• four membered transition state leads to syn stereochemistry

• no carbocation rearrangements

H2, Pd/C

• syn stereochemistry

• reduction reaction

• only for alkenes

mCPBA, CH2Cl2

• former is a peroxyacid

• syn stereochemistry

• oxidation reaction

1. OsO4

2. NaHSO3, H2O

• formation of a diol

• syn stereochemistry

• oxidation reaction

1. O3

2. Zn, H3O+

• cleavage of alkene

• 2 new carbonyls formed

• oxidation reaction

KMnO4, H3O+

• cleavage of alkene

• oxidation reaction

• 1 hydrogen - carboxylic acid

• 2 hydrogens - CO2

CHCl3, KOH

• formation of cyclopropane

• reaction includes formation of a carbene, which reacts w the double bond

• syn stereochemsitry

oxidation reactions

• C-H bonds broken

• C-O bonds formed, gaining

reduction reactions

• C-O bonds broken, losing

• C-H bonds formed

oxidizing agents

• have O-O bonds

• have metal-O bonds