Return to Contents Chapter 15: Alcohols, Diols and Thiols Ch 15 contents
Alcohols, Diols and Thiols Answers
 
Qu 1: (a) Since 1-propanol would be the anti-Markovnikov alcohol, use BH3 then H2O2 /  NaOH
(b) Need to add a C, so open epoxide with an organometallic reagent, e.g. CH3MgBr in Et2O or THF, followed by an acidic work-up.
(c) Right number of C, so simple reduction using either LiAlH4 in THF then acidic work-up or NaBH4 in EtOH
(d) Right number of C, so simple reduction using LiAlH4 in THF then acidic work-up. NaBH4 will not reduce RCO2H
(e) Reduction of a propanoate ester with LiAlH4 in THF will give the primary alcohol.
Qu 2: (a) Since 2-propanol would be the Markovnikov alcohol, use aq. H2SO4 / heat.
(b) Right number of C, so simple reduction using either LiAlH4 in THF then acidic work-up or NaBH4 in EtOH
(c) Need to add a C, use an organometallic reagent, e.g. CH3MgBr in Et2O or THF, followed by an acidic work-up.
(d) Right number of C, just need to change the functional group. Use aq. NaOH.
Qu 3: (a) cis-1,2-cyclohexanediol
(b) trans-1,2-cyclohexanediol
(c) (R,R)- and (S,S)-2,3-butanediol
(d) meso-2,3-butanediol
(e) (R,R)- and (S,S)-2,3-butanediol. Compare this to reaction (d), changing the stereochemistry of the overall additon process to anti means that the products will be diastereomeric with those in (d).
(f) They are diastereomers. Since the addition is syn, the relationship is defined by the relationship of the alkene starting materials.
Qu 4: (a) Thionyl chloride converts ROH to RCl, so benzyl chloride, C6H5CH2Cl.
(b) A Williamson ether synthesis, giving C6H5CH2OCH2CH3
(c) Under aqueous, the product will be benzoic acid, C6H5CO2H
(d) With the more selective oxidation conditions, the product will be benzaldehyde, C6H5CHO
(e) An ester preparation giving benzyl ethanoate, CH3CO2CH2C6H5
Qu 5: In each case, disconnect the alcoholic portion from the acid portion:
Qu 6: Periodic acid, HIO4, causes oxidative cleavage of 1,2-diols. 
        In the case of a cyclic diol, this would break the ring.  The product here would be 1,6-hexanedial.
Qu 7: The best method for ether synthesis is the Williamson method from an alcohol and an alkyl halide.
 
(a) This is the best disconnection to a primary halide (good SN2) and the tertiary alcohol. The tertiary bromide would be prone to elimination.
(b) This is the only choice since aryl bromides do not undergo substitution, we must make it the alcoholic component.
(c) A symmetrical cyclic ether so we can disconnect either C-O bond, it makes no difference.