Organic Chemistry by Brown, Iverson, Anslyn, Foote | Mayya's Study Guide

Chapter 10: Alcohols

Table of contents of main topics:

Nomenclature of Alcohols
Reaction of Alcohols with Active Metals
Conversion of Alcohols to Haloalkanes and Sulfonates
Acid-Catalyzed Dehydration of Alcohols
The Pinacol Rearrangement
Oxidation of Alcohols
Periodic Acid Oxidation of Glycols
Summary of Alcohol Reactions

Nomenclature of Alcohols

Find the longest continuous carbon chain and start numbering from the end closest to the OH group. End the parent chain name with "ol" and put a number in front of the name signifying the carbon to which OH is attached.
If the OH group is on a ring, start counting from the carbon that has the OH group.
Proceed with naming substituted just like we did for alkanes and put the name together with substituents first (in alphabetical order) followed by the name of the parent.
If there are multiple OH groups, use "diol" (2), and "triol"(3)...
For molecules containing a double bond and an alcohol use parent name ending in "en"-#-"ol"

Alcohols can be classified as:

Primary = OH is on a carbon that is attached to one carbon only

Secondary = OH is on a carbon that is attached to two other carbons

Tertiary = OH is on a carbon attached to three more carbons

Reaction of Alcohols with Active Metals

Alcohols will get deprotonated when reacting with metals such as NaH.

Conversion of Alcohols to Haloalkanes and Sulfonates (How to make alcohol into a good leaving group).

Alcohols are very poor leaving groups. We oftentimes need to convert an alcohol into a good leaving group to do further reactions on the molecule. The reagents that make alcohol into a good leaving group are: HCl, HBr, HI, TsCl, PBr3 and SOCl2.

The reaction of alcohol with HBr or HCl yields Br or Cl instead of the OH group. Please note that these reactions are capable of rearrangements and do not always give the desired product.

Tertiary and secondary alcohols will reach with HX with Sn1, while primary alcohols with no extensive beta branching will undergo SN2.

Mechanism of the reaction of alcohol with HCl

The reaction of alcohol with TsCl (tosyl chloride) produces ROTs ( alkyl tosylate). OTs is an excellent leaving group. In this reaction, the stereochemistry of OH as it gets converted to OTS remains the same. For example, if OH was on a wedge, OTs would be on a wedge as well.

Preparation Of Sulfonate Esters Using sulfonyl chloride (OH into OTs)

PBr3 (phosphorus tribromide) turns OH into Br (works on most primary and secondary alkyl halides). Results in INVERSION of stereochemistry due to the SN2 reaction in the second step.

Reaction of alcohol with PBr3 and its mechanism

SOCl2 (thionyl chloride) with pyridine converts OH into Cl (also works on primary and secondary alcohols). It results in inversion of stereochemistry just like PBr3.

Reaction Of Alcohols With PBr3 and SOCl2

Acid-Catalyzed Dehydration of Alcohols

Alcohol can be reduced to an alkene via E1 elimination reaction. The reagent for the reaction is usually H2SO4/heat (sulfuric acid).

Mechanism for turning alcohol into an alkene.

The Pinacol Rearrangement

This is just another type of carbocation rearrangement.

First alcohol get protonate and becomes a good leaving group. OH2+ leaves to form a carbocation, which is followed by an alkyl shift. The electrons from OH go down to the carbocation to form a double bond and finally, OH gets deprotonated in the last step to make a ketone.

Oxidation of Alcohols

Secondary Alcohols

Secondary alcohols (OH is on a carbon that is attached to two other carbons) can be oxidized to ketones (OH turns into a =O), using a variety of reagents including: Na2Cr2O7 with H2SO4, PCC with CH2Cl2, CrO3 with H3O+ (Jones reagent), acetone and NaOCl/TEMPO, DMP, or 1. (COCl)2, DMSO 2. Et3N.

Primary Alcohols

Primary alcohols are molecules where the OH group is on a carbon that is attached to one carbon only. Depending on the reagent primary alcohols can be oxidized into either aldehydes or carboxylic acids. Na2Cr2O7 with H2SO4 and Jones reagent (CrO3 with H3O+) oxidize primary alcohols all the way to carboxylic acids, while PCC with CH2Cl2 stops at the aldehyde.