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Unit 6 – Alcohols and Ethers. Types of Alcohols Nomenclature Properties of Alcohols Synthesis of Alcohols Reactions of Alcohols. Types of Alcohols. Alcohol: organic compound containing one or more hydroxyl (OH) groups. - PowerPoint PPT Presentation
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Unit 6 – Alcohols and EthersTypes of AlcoholsNomenclatureProperties of
AlcoholsSynthesis of AlcoholsReactions of Alcohols
Types of Alcohols Alcohol:
organic compound containing one or more hydroxyl (OH) groups.
Alcohols are often classified by the type of carbinol carbon atom present the carbon bonded to the OH group
CH3OH
CH3CH2OH
CH3CHCH3
OH
CH3OH
CH3CH2OH
CH3CHCH3
OH
CH3OH
CH3CH2OH
CH3CHCH3
OH
Methanolwood alcohol
Ethanoldrinking alcohol
Isopropyl alcoholrubbing alcohol
CH3OH
CH3CH2OH
CH3CHCH3
OHOH
CH3
H3C
CH3
CCH3OH
CH3CH2OH
CH3CHCH3
OH
Types of Alcohols Primary alcohol:
the carbinol carbon is attachedto one other carbon atom
Secondary alcohol: the carbinol carbon is attached
to two other carbon atoms
Tertiary alcohol: the carbinol carbon is attached
to three other carbon atoms
CH3OH
CH3CH2OH
CH3CHCH3
OH
Types of Alcohols Diol:
an alcohol with two OH groups
Glycol: a vicinal diol
OH groups on adjacent carbons
OHCH3
HO OH
OHCH3
HO OH
HO
OH OHCH3
OH
CH3
Ethylene glycolcar antifreeze
propylene glycolmedicine, food
Types of Alcohols Phenol:
a compound with a hydroxyl group bonded directly to an aromatic (benzene) ring
Thiols: an organic compound with an SH group
sulfur analog of alcoholsalso called mercaptans
CH3CH2CH2CH2SH
OHphenol
3-methyl-1-butanethiolCH3CHCH2CH2SH
CH3CH=CHCH2SH
OH
CH3
IR of Alcohols Alcohols typically exhibit a strong, broad,
rounded peak at about 3300 cm-1+ for the O-H bond.
SDBSWeb : http://riodb01.ibase.aist.go.jp/sdbs/ (National Institute of Advanced Industrial Science and Technology, 11/1/09)
IR of Alcohols In the absence of hydrogen bonding, the
O – H peak can be relatively sharp and hard to distinguish from an N – H peak. The frequency for an O-H peak in the
absence of hydrogen bonding is typically somewhat higher (~3600 cm-
1).
The O-H peak for a carboxylic acid is much broader and typically spans the distance from ~2500 – 3500 cm-1.
IR of Alcohols
acid O-H acid O-H
alcohol O-H w/hydrogen bonding
alcohol O-H w/o hydrogen bonding
Nomenclature IUPAC Naming System for Alcohols:
Find the longest continuous chain that contains the carbinol carbon atom
Drop the “e” from the corresponding alkane name and add the suffix “ol”
a substituted pentanolOH
CH3
Nomenclature IUPAC Naming System for Alcohols:
Number the longest chain starting from the end closest to the OH group.OH takes priority over double and triple bonds
OH group is assumed to be on C #1 on a cycloalkane ring
Name and number all substituents as with an alkane or alkene.
(2R, 3R)-3-methyl-2-pentanol
Don’t forget R or S if appropriate.
OH
CH3
Nomenclature To name an alcohol that contains a
double bond: use “ol” suffix after the name of the
alkene (drop the last “e”) number the chain to give the carbinol
carbon the lowest possible number place the position number for the C=C
in front of the base name (or before the “en”) and the position number for the OH in front of the “ol” suffix
OHCH3
4-methylhex-5-en-1-ol4-methyl-5-hexen-1-ol
Nomenclature To name diols:
use suffix “diol” after the name of the alkane (keep the ending “e”)
indicate the position of each OH groupplace position of each OH group in front of the base name or in front of the suffix “diol”
OH
OH
2, 3-pentanediolor
pentane-2, 3-diol
Nomenclature To name thiols:
Use the same rules for naming alcoholsuse “thiol” suffix instead of “ol” suffix
SH2-pentanethiol
SH
CH3
3-methyl-2-pentanethiol
Nomenclature Common names are often used with
phenols:
SH
CH3
OHBr
NO2
OH
Cl
OH
SH
CH3
OHBr
NO2
OH
Cl
OH
SH
CH3
OHBr
NO2
OH
Cl
OH
SH
CH3
OHBr
NO2
OH
Cl
OH
OH
phenol
2-bromophenol or
ortho-bromophenol
3-nitrophenol or
meta-nitrophenol
4-chlorophenol or
para-chlorophenol
ortho = 1,2 meta = 1,3 para = 1,4
Nomenclature Common names are often used with
phenols:OH
CH3
OHOH
OH
OH
OH
OH
OHCH3
OHOH
OH
OH
OH
OH
OHCH3
OHOH
OH
OH
OH
OH
OHCH3
OHOH
OH
OH
OH
OH
2-methylphenolortho-cresol
Benzene-1,2-diolcatechol
Benzene-1,3-diolresorcinol
Benzene-1,4-diolhydroquinone
OH OHOH
OH
OH
OH
OH
CH3
4-methylphenolpara-cresol
NomenclatureExample: Name the following compounds:
OH
CH3
OH
CH3
SH
OH
CH3
SH
OH
OH
OH
CH3
SH
OH
OH
OHBr
NomenclatureExample: Draw the structures of the following compounds.
3-isopropyl-2-methyl-2-hexanol
trans-2-bromocyclohexanol
(E)-2-chloro-2-buten-1-ol
Properties of Alcohols The physical properties of alcohols are
strongly influenced by the presence of the hydrophilic (“water loving”) OH group. The OH group is capable of forming
hydrogen bonds with other alcohol groups or with water.
Properties of Alcohols Due to hydrogen bonding, alcohols have
significantly higher boiling points than alkanes with comparable molecular weights.
CH3CH2OH MW = 46BP = 78oC
CH3CH2CH3 MW = 44 BP = - 42oC
Properties of Alcohols BP increases as the amount of hydrogen
bonding increases: 1-propanol BP = 97oC
1,2-propanediol BP = 188oC(propylene glycol)
1,2,3-propanetriol BP = 290oC(Glycerol)
Physical Properties
Alcohols with 1-3 carbons are soluble in water.
Properties of Alcohols Solubility decreases as the size of the
alkyl group increases. 1-hexanol is less soluble than ethanol
Solubility increases as the alkyl group becomes more compact/spherical. t-butyl alcohol is more soluble than 1-
butanol.
Solubility increases with increasing number of OH groups.
Acidity of Alcohols and Phenols The acidity of alcohols varies widely and
can be expressed using the acid dissociation constant, Ka
ROH + H2O RO- + H3O+
Ka = [RO-][H3O+] pKa = -log Ka[ROH]
Acidity increases as: Ka increases pKa decreases
Alkoxide ion
Acidity of Alcohols and Phenols Structural trends and acidity:
Acidity of H2O, CH3OH, and CH3CH2OH are similar. (pKa = 15.7, 15.5, and 15.9 respectively)
Acidity decreases as number of carbons in the R group increases.CH3OH pKa = 15.5t-butyl alcohol pKa = 18.0
Acidity of Alcohols and Phenols Structural trends and acidity:
Acidity increases with the addition of electron-withdrawing halogens
ClOH OH
pKa = 14.3 pKa = 15.9
C
OH
CH2OHClCl
Cl
pKa = 12.2
Acidity of Alcohols and Phenols Structural trends and acidity:
Phenols are more acidic than water or alcohols
C
OH
CH2OHClCl
Cl
OH
C
OH
CH2OHClCl
Cl
OH
OHpKa = 18.0 pKa = 10.0
O O
O
O
O O
O
O
O O
O
O
O O
O
O
Acidity of Alcohols and Phenols Phenols are stronger acids than alcohols.
React readily with aqueous NaOH
Phenols are soluble in aqueous strong base solutions but are insoluble in aqueous NaHCO3.
+ NaOH + H2O
NaOH O +
Sodium phenoxide
Acidity of Alcohols and Phenols Since alcohols are very weak acids, a very
strong base is used to remove the acidic proton.
Unless they are water soluble, alcohols are not soluble in aqueous base solution.
CH3CH2OH Na(s) CH3CH2O-Na+ H2 (g)+ 1/ 2+
OH + K (s) O-K+ + 1/ 2 H2 (g)
ROH + NaH THF RO-Na+ + H2 (g)
Synthesis of Alcohols Nucleophilic Substitution on an alkyl halide
SN2 conditions most usefulstrong nucleophilemethyl > 1o > 2o
inversion of configuration
C NaOHacetone
HOR
XH
HCH
H
R
Synthesis of Alcohols Acid Catalyzed Hydration (Hydrolysis) of
Alkenes
Markovnikov product formed Equilibrium process Less useful synthetically than other
methods rearrangements often occur
C NaOHacetone
HO
CH2SO4
H2O C
RX
HH
CH
H
R
C CR R
OH
Synthesis of Alcohols Oxymercuration-Demercuration of
Alkenes
Markovnikov product
Anti addition to double bond
C NaOHacetone
HO
C(1) Hg(OAc)2 (aq)
(2) NaBH4C
RX
HH
CH
H
R
C CR R
OH
H
Synthesis of Alcohols Hydroboration-Oxidation of Alkenes
Anti-Markovnikov product
Syn addition to double bond
C NaOHacetone
HO
C(1) BH3-THF
(2) H2O2, NaOH C
RX
HH
CH
H
R
C CR R
HOH
Synthesis of Alcohols Syn Hydroxylation of Alkenes
Syn addition to double bond
Reagents: OsO4, H2O2
cold, dilute KMnO4, OH-or
C NaOHacetone
HO
C COsO4, H2O2
RX
HH
CH
H
R
C CR R
OH OH
Synthesis of Alcohols Anti-Hydroxylation of Alkenes
epoxide intermediate
Anti addition to double bond Common peroxyacids:
CH3CO3H MCPBA
C NaOHacetone
HO
C C(1) RCO3H(2) H+/H2O
RX
HH
CH
H
R
C CR R
OH
OH