ORGANIC CHEMISTRY - CHAPTER 9: FURTHER REACTIONS OF ALCOHOLS AND THE CHEMISTRY OF ETHERS

Important Concepts

1. The reactivity of ROH with alkali metals to give alkoxides and hydrogen follows the order R = CH3 > primary > secondary > tertiary.
2. In the presence of acid and a nucleophilic counterion, primary alcohols undergo SN2 reactions. Secondary and tertiary alcohols tend to form carbocations in the presence of acid, capable of E1 and SN1 product formation, before and after rearrangement.
3.  Carbocation rearrangements take place by hydride and alkyl group shifts. They usually result in interconversion of secondary carbocations or conversion of a secondary into a tertiary carbocation. Primary alkyl oxoniumions can rearrange by a concerted process consisting of loss of water and simultaneous hydride or alkyl shift to give secondary or tertiary carbocations.
4. Synthesis of primary and secondary haloalkanes can be achieved with less risk of rearrangement by methods using inorganic esters.
5. Ethers are prepared by either the Williamson ether synthesisor by reaction of alcohols with strong nonnucleophilic acids. The first method is best when SN2 reactivity is high. In the latter case, elimination (dehydration) is a competing process at higher temperatures.
6.  Crown ethersand cryptandsare examples of ionophores,polyethers that coordinate around metal ions, thus rendering them soluble in hydrophobic media.
7. Whereas nucleophilic ring opening of oxacyclopropanesby anions is at the less substituted ring carbon according to the rules of the SN2 reaction, acid-catalyzed opening favors the more substituted carbon, because of charge control of nucleophilic attack.
8. Sulfur has more diffuse orbitals than does oxygen. In thiols,the S – H bond is less polarized than the O – H bond in alcohols, thus leading to diminished hydrogen bonding.Because the S – H bond is also weaker than the O – H bond, the acidityof thiols is greaterthan that of alcohols.
9.  Note on color use: Throughout the main parts of the text, beginning in Chapter 6, reacting species in mechanisms and most examples of new transformations are color coded red for nucleophiles, blue for electrophiles, and green for leaving groups. Color coding is notused in exercises, summaries of new reactions, or chapter-end problems

From "Organic Chemistry" Textbook of VOLLHARDT & SCHORE

ORGANIC CHEMISTRY - CHAPTER 8: HYDROXY FUNCTIONAL GROUP: ALCOHOLS

Important Concepts

1. Alcohols are alkanols in IUPAC nomenclature. The stem containing the functional group gives

the alcohol its name. Alkyl and halo substituents are added as prefixes.

2. Like water, alcohols have a polarized and short O – H bond. The hydroxy group is hydrophilic

and enters into hydrogen bonding. Consequently, alcohols have unusually high boiling points

and, in many cases, appreciable water solubility. The alkyl part of the molecule is hydrophobic.

3. Again like water, alcohols are amphoteric: They are both acidic and basic. Complete deprotonation to an alkoxide takes place with bases whose conjugate acids are considerably weaker than the alcohol. Protonation gives an alkyloxonium ion. In solution, the order of acidity is primary .secondary .tertiary alcohol. Electron-withdrawing substituents increase the acidity (and reduce the basicity).

4. The conversion of the electrophilic alkyl group in a haloalkane, C^δ+ − X^δ-, into its nucleophilic analog in an organometallic compound, C^δ- − M^δ+, is an example of reverse polarization.

5. The carbon atom in the carbonyl group, C = O, of an aldehyde or a ketone is electrophilic and therefore subject to attack by nucleophiles, such as hydride in hydride reagentsor alkyl in organometallic compounds. Subsequent to aqueous work-up, the products of such transformations are alcohols.

6. The oxidation of alcohols to aldehydes and ketones by chromium(VI) reagents opens up important

synthetic possibilities based on further reactions with organometallic reagents.

7.  Retrosynthetic analysis aids in planning the synthesis of complex organic molecules by identifying

strategic bonds that may be constructed in an efficient sequence of reactions.

From "Organic Chemistry" Textbook of VOLLHARDT & SCHORE