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Ch10 - 2 10 C hapter I 0 A lcohols S olutions 211 S...

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210 Solutions Chapter I 0: Alcohols CHAPTER 10 Solutions to the Problems Problem 10.1 Write IUPAC names for these alcohols, including configuration for (a): Solutions 211 Chapter 10: Alcohols Emblem 10.6 Predict the position of equilibrium for this acid-base reaction. o II CH 3 CH 2 6 Na+ + CH 3 -:C-OH ~ CH 3 CH 2 0H Acetic acid is the stronger acid; equilibrium I~es' to the right. o II CH 3 CH 2 0- Na+ + CH 3 -C-OH --==="'-- CH 3 CH 2 0H pK a 4.76 pK a 15.9 (stronger (stronger (weaker (weaker base) acid) acid) base) Problem 10.7 Show how to convert (R)-2-pentanol to (S)-2-pentanethiol via a tosylate: OH SH ~ ? ~ (R)-2-Pentanol (S)·2-Pentanethiol In the first step, the -OH group is converted to the good leaving group -OTs by treatment with tosyl chloride (Ts-CJ) in pyridine. ~TS Pyridine Step 1: + Ts-CI ~ (R)-2-Pentanol Next the good nucleophile HS- is used to carry out an SN2 reaction and displace the -OTs group. Note that the inversion of stereochemistry seen with SN2 reactions insures that the desired (S) isomer of 2-pentanethiol is produced. 9Ts ~2 Step 2: (inversion) (S)-2-Pentanethiol Problem 10.8 Draw structural formulas for the alkenes formed by acid-catalyzed dehydration of each alcohol. Where isomeric alkenes are possible, predict which is the major product. ~ acid-catalyzed dehydration. + (a) 2-Methyl-2-butanol ~ Major acid-catalyzed CfOH dehydration. ~CH3 + crC~ (b) CH 3 1- Methylcyclopentanol Major (b) (a)HO~ (S)-Z-Methyl-l-butanol 1- Methylcyclopentanol Problem 10.2 C"lassify each alcohol as primary, secondary, or tertiary. (e) (a)"""~OH Primary Secondary Secondary Problem iO.3 Write IUPAC narries for these unsaturated alcohols. OH (a) ~OH (b) N 3-Buten-l-01 (R)-3-Buten-Z-ol Problem lOA Arrange these compound~ in order of increasing boili~g point. HO~OH Heptane 1,5-Pentanediol In order of increasing boiling point they are: ~OH Heptane I-Hexanol bp 98.4°C bp IS7"C Hydrogen bonding, or lack of it, is the key. Both I-hexanol and 1,4-pentanediol can associate by hydrogen" bonding, so their boiling points are substantially higher than heptane. Because I,S-pentaliediol has more sites for hydrogen bonding, it has a higher boiling point than I-hexanoI. Problem 1O.5 Arrange these compounds in order of increasing solubility in water. HO~' CI~cr HO~ I-Butanol I-Propanol 1,2.Dichloroethane . CH 3 (d)~ "-J "OH Tertiary ~OH I-Hexanol I,S-Pentanediol bp 242°C In order of increasing solubility in water, they are: CI ..... ../'-.. "'-./ 'CI HO~ 1,2-Dichloroethane I-Butanol Slightly soluble 8 g/100 gHzO HO~ I .. Propanol Soluble in all proportions
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Solutions Chapter 10: Alcohols 212 Problem 10.9 Propose a mechanism to account for this acid-catalyzed dehydration. ex + ~o warm (racemic) This reaction can best be explained as an acid catalyzed El reaction with a carbocation rearrangement. The first steps irivol~e protonation of the -OH group; followed by loss of H20 to give a r carbocation.
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