課件columbia有機(jī)化學(xué)有機(jī)化學(xué)課件15.html

1、15.13Preparation of ThiolsNomenclature of Thiols1) analogous to alcohols, but suffix is -thiol rather than -ol2) final -e of alkane name is retained, not dropped as with alcoholsNomenclature of Thiols1) analogous to alcohols, but suffix is -thiol rather than -ol2) final -e of alkane name is retained

2、, not dropped as with alcoholsCH3CHCH2CH2SHCH33-Methyl-1-butanethiolThiols are prepared from alkyl halidesSN2 using thiourea as source of nucleophilic sulfurthe product is an isothiouronium saltH2NSH2NCRXH2NSH2NCR+Thiols are prepared from alkyl halides H2NSH2NCR+hydrolysis in base converts the isoth

3、iouronium salt to the desired thiolNaOHH2OH2NOH2NCR+HSCH3(CH2)4CH2BrCH3(CH2)4CH2SH1-Hexanethiol (84%)1. (H2N)2CS2. NaOHExample15.14Properties of Thiols1. low molecular weight thiols have foul odors2. hydrogen bonding is much weaker in thiols than in alcohols3. thiols are stronger acids than alcohols

4、4. thiols are more easily oxidized than alcohols; oxidation takes place at sulfurProperties of Thiolshave pKas of about 10; can be deprotonated in aqueous base.stronger acid(pKa = 10)weaker acid(pKa = 15.7)Thiols are stronger acids than alcoholsHRSOHRSHOH+Oxidation of thiols take place at sulfurthio

5、ldisulfideRSHRSSRthiol-disulfide redox pair is important in biochemistryother oxidative processes place 1,2, or 3 oxygen atoms on sulfurOxidation of thiols take place at sulfurthioldisulfidesulfinic acidsulfonic acidRSHRSSRsulfenic acidRSOHRSOHO+RSOHO2+OHSCH2CH2CH(CH2)4COHSHO2, FeCl3(CH2)4COHa-Lipoi

6、c acid (78%)Example: sulfide-disulfide redox pairOOSS15.15Spectroscopic Analysis of AlcoholsOH stretching: 3200-3650 cm1 (broad) CO stretching: 1025-1200 cm1 (broad) Infrared SpectroscopyFrancis A. Carey, Organic Chemistry, Fourth Edition. Copyright 2000 The McGraw-Hill Companies, Inc. All rights re

7、served.200035003000250010001500500Wave number, cm-1Figure 15.4: Infrared Spectrum of CyclohexanolOHCHCOOHchemical shift of OH proton is variable; dependson temperature and concentrationOH proton can be identified by adding D2O; signal for OH disappears (converted to OD)HCO signal is less shielded th

8、an HCH1H NMRCOHHd 3.3-4 ppmd 0.5-5 ppm01.02.03.04.05.06.07.08.09.010.0Chemical shift (d, ppm)Figure 15.5 (page 607)CH2CH2OHchemical shift of COH is d 60-75 ppmCO is about 35-50 ppm less shielded than CH13C NMRCH3CH2CH2CH3CH3CH2CH2CH2OHd 13 ppmd 61.4 ppmUV-VISUnless there are other chromophores in th

9、emolecule, alcohols are transparent aboveabout 200 nm; lmax for methanol, forexample, is 177 nm.molecular ion peak is usually smalla peak corresponding to loss of H2Ofrom the molecular ion (M - 18) isusually presentpeak corresponding to loss of analkyl group to give an oxygen-stabilized carbocation is usuallyprominentMass Spectrometry of Alcoholsmolecular ion peak is usually smalla peak corresponding to loss of H2Ofrom the molecular ion (M - 18) isusually presentpe