1559T_ch08_132-14710/30/0511:59Pa9e134 ⊕ EQA 134.Chapter 8 HYDROXY FUNCTIONAL GROUP:ALCOHOLS:PROPERTIES,PREPARATION,AND STRATEGY OF SYNTHESIS onge han any other dipole-dipole attraction.which is why it merits the special name ydroger CH3 CHs 08- dimcylche Remember.the requireme y elec tract them 8-3.Acidity and Basicity of Alcohols If you understa the acidic and basic nature of water,then you will need to leam only a little bit that is new here with alcohols.The equilibrium processes are qualitatively similar: H0+H20H0 As a ROH RO The differences arise from the presence of the R group (instead of an H).which can affect the relative stabil- n substituents in R(such as halogens) will stabilize RO，however,there y making ROH a stronger acid(see entries in Table 8-2). The acidity and n many or their re hen an alcohol d i ts as an cid and loses a proton,it be .a good nucleophile and strong base capable ceaterimgint 2 and SN reaction of alcohols coming up later. 85 Synthesis of Alcohols by Nucleop philic subs be prepared by 2displacement reactions of HOth appropriate substrates (.gprima haloalkanes).This approach sor netimes work secondar but elir n often inter eres.To phile.However.the chemistr n the ofhe c vid much more versatile and reliable means of synthesizing alcohols. nd Redu ecursors (starting materials)for the synthe The same process converts ketones to secondary alcohol much stronger than any other dipole–dipole attraction, which is why it merits the special name hydrogen bonding. Remember, the requirements for hydrogen bonding are hydrogens, such as those attached to very elec￾tronegative atoms (e.g., N, O, F), and electronegative atoms with lone pairs (again, mainly N, O, and F) to at￾tract them. 8-3. Acidity and Basicity of Alcohols If you understand the acidic and basic nature of water, then you will need to learn only a little bit that is new here with alcohols. The equilibrium processes are qualitatively similar: The differences arise from the presence of the R group (instead of an H), which can affect the relative stabil￾ities of the three species involved. Simple alkyl groups generally destabilize both ROH2 and RO
in solu￾tion, relative to ROH, more than H3O and OH
are destabilized, relative to water. So most ordinary alcohols are both weaker acids and weaker bases than water. Electron-withdrawing substituents in R (such as halogens) will stabilize RO
, however, thereby making ROH a stronger acid (see entries in Table 8-2). The acidity and basicity of alcohols will play major roles in many of their reactions. When an alcohol acts as a base and is protonated by a strong acid, becoming ROH2 , it then contains a good leaving group and is capable of both substitution and elimination reactions (Chapter 9). When an alcohol acts as an acid and loses a proton, it becomes RO
, a good nucleophile and strong base capable of entering into E2 and SN2 reactions (Chapters 6 and 9). So this chemistry really serves as a general entry to the more extensive survey of reactions of alcohols coming up later. 8-5. Synthesis of Alcohols by Nucleophilic Substitution After a section on industrial methods, a review covering SN2 and SN1 routes to alcohols is presented. Primary alcohols may be prepared by SN2 displacement reactions of HO
with appropriate substrates (e.g., primary haloalkanes). This approach sometimes works for secondary systems, but elimination often interferes. To a limited extent, both secondary and tertiary alcohols may be formed in SN1 reactions with water as the nucleo￾phile. However, the chemistry described in the remainder of the chapter provides much more versatile and reliable means of synthesizing alcohols. 8-6. Oxidation and Reduction Carbonyl compounds such as ketones and aldehydes are useful precursors (starting materials) for the synthe￾sis of alcohols. Reaction with the hydride reagents NaBH4 and LiAlH4 converts aldehydes to primary alcohols. The same process converts ketones to secondary alcohols. These hydride reductions are the first of many H3O H2O HO
ROH2 ROH RO
As a base (adds H) As an acid (loses H) O O CH3 CH3 CH3 CH3

O O O O H H H CH3 CH3 H CH3 CH3


Strong “hydrogen bonding” type dipole–dipole attractions in methanol Weak dipole–dipole attractions in dimethyl ether 134 • Chapter 8 HYDROXY FUNCTIONAL GROUP: ALCOHOLS: PROPERTIES, PREPARATION, AND STRATEGY OF SYNTHESIS 1559T_ch08_132-147 10/30/05 11:59 Page 134