440 CHAPTER 12 Reactions of Alcohols, Ethers, Epoxides, and Sulfur-Containing CompoundsHoward J. Lucas (1885–1963)
was born in Ohio and earned B.S.
and M.S. degrees from Ohio State
University. He published a
description of the Lucas test in- He was a professor of
chemistry at the California
Institute of Technology.
PROBLEM 1The observed relative reactivities of primary, secondary, and tertiary alcohols with a
hydrogen halide are If secondary alcohols underwent an reaction
rather than an reaction with a hydrogen halide, what would be the relative reactivities
of the three classes of alcohols?Because the reaction of a secondary or a tertiary alcohol with a hydrogen halide is
an reaction, a carbocation is formed as an intermediate. Therefore, we must check
for the possibility of a carbocation rearrangement when predicting the product of the
substitution reaction. Remember that a carbocation rearrangement will occur if it leads
to formation of a more stable carbocation (Section 4.6). For example, the major
product of the reaction of 3-methyl-2-butanol with HBr is 2-bromo-2-methylbutane,
because a 1,2-hydride shift converts the initially formed secondary carbocation into a
more stable tertiary carbocation.PROBLEM 2Give the major product of each of the following reactions:a. c.b. d.12.2 Amines Do Not Undergo Substitution Reactions
We have just seen that alcohols are much less reactive than alkyl halides in substitution
reactions. Amines are even less reactive than alcohols. The relative reactivities of
an alkyl fluoride (the least reactive of the alkyl halides), an alcohol, and an amine can
be appreciated by comparing the pKavalues of the conjugate acids of their leavingCHCH 3CH 3OH+ HCl
OH ∆CH 3
+ HClCH 3 C CHCH 3CH 3 OHCH 3
+ HBr
∆
CH 3 CH 2 CHCH 3OH+ HBr
∆SN 1SN 13 ° 72 ° 71 °. SN 2+ H 2 OBr−secondary carbocation tertiary carbocationCH 3 CHCHCH 3OH +OH
HCH 3 CHCHCH 3CH 3CH 3 CHCHCH 3CH 3 CHCHCH 3+ HBrBr−CH 3 CH 3CH 3 CH 3Br BrCH 3 CCH 2 CH 3+CH 3CH 3 CCH+ 2 CH 33-methyl-2-butanol2-bromo-3-methyl-
butane
minor product1,2-hydride
shift2-bromo-2-methyl-
butane
major productBRUI12-437_480r3 27-03-2003 11:50 AM Page 440