Transcript Alcohols, etc.

Power Point to Accompany
Principles and Applications of
Inorganic, Organic, and
Biological Chemistry
Denniston, Topping, and Caret
4th ed
Chapter 13
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
13-1
Formulas
Alcohols have the general formula R-OH
Ethers have the formula R-O-R
R can be aliphatic or aromatic
Phenols have the formula Ar-OH
Ar must be an aromatic ring (eg.
Benzene)
Thiols have the formula R-SH
Disulfides have the formula R-S-S-R
R may be aliphatic or aromatic
13-2
13.1 Alcohol: Structure and Properties
Low molecular weight alcohols (up to 5-6
carbons) are soluble in water because they
are polar and hydrogen bond (through the
OH) with the water molecule.
Eg. CH3CH2OH solube but CH3OCH3 barely
soluble.
CH3CH2CH2CH2OH, 7 g per 100 mL but
HOCH2CH2CH2CH2OH is very soluble!
(two OH groups)
13-3
Alcohol Boiling Pts
Alcohols have abnormally high bp
relative to their molecular weights due
to their ability to hydrogen bond.
CH3
CH3CH
CH2
2O
O
H
H
H
O CH2 CH3
13-4
Alcohol Boiling Pts-2
Trends in boiling points (Similar MW)
CH3CH2CH3 bp -42
oC
bp -23
oC
CH3O CH3
CH3CH2OH bp +78.5
oC
13-5
13.2 Alcohols: Nomenclature
IUPAC: based on the longest chain
containing the OH carbon.
The e of the alkane name is replaced
with ol. The chain is numbered
from the end giving the OH carbon
the lower number. The name is
prefixed with the number indicating
the position of the OH group.
For cyclic alcohols, the OH is at C-1.
13-6
Alcohols: names-2
Name the alcohols.
CH3
CH3CH CH CH3
OH
CH3
OH
3-methyl-2-butanol
3-methylcyclohexanol
OH must be at C-1 13-7
Alcohols: names-3
The common names for alcohols consist
of the alkyl group name, a space, and
the word alcohol. Name:
CH3
CH3 C CH3 CH3CH CH3
OH
OH
t-butyl alcohol
isopropyl alcohol
13-8
13.3 Alcohol Examples of Interest
CH3CH2OH
HO CH2CH2OH
ethyl alcohol
(drinking alcohol)
ethylene glycol
(antifreeze)
OH
HO CH2CH CH2OH
glycerol
(in fats,
a moisturizer)
13-9
13.4 Classes of Alcohols
CH3CH2OH
CH3CH CH3
OH
CH3
CH3 C CH3
OH
Primary:
one R group on
alcohol C
Secondary:
Two R groups on
alcohol C
Tertiary:
Three R groups on
alcohol C
13-10
13.5 Reactions Involving Alcohols: prep
1. Form alkenes by adding water
(hydration)
Major Product
CH3 CH CH2
H2O, H+
OH
CH3 CH CH3
OH
CH3 CH2 CH2
13-11
Alcohols Rxns: prep
2. Form aldehydes/ketones by reduction
hydrogenation with H2.
o
2
O
OH
H2,
CH3 C CH3 Pt/Pd/Ni CH3 CH CH3
O H,
1o OH
2
CH3 C H Pt/Pd/Ni CH3 CH2
13-12
Alcohols: reactions
1. Alcohols dehydrate with heat and strong
acid to give alkenes. Zaitsev’s rule (most
substituted alkene) applies to determine the
major product.
warm
CH3
H2SO4 or
CH3CH CH CH3H PO
3
OH
CH3
CH3C CH CH3
Major product
4
CH3
CH3CH CH CH2
Minor product 13-13
Alcohols: reactions
Zaitsev’s rule applied again
CH3
OH
warm
H2SO4 or
H3PO4
H may leave from
CH3
major product:
more substituted
alkene
13-14
Alcohols: reactions
2. Oxidation
Secondary alcohols oxidize to ketones. (The
reaction is also an elimination of 2H.)
The usual oxidizing agent is a Cr(VI) species.
Tertiary alcohols do not oxidize as there is no
H on the carbonyl carbon to remove!
OH CrO3, py or
O
K2Cr2O7
2H eliminated
13-15
Alcohols: reactions
Primary alcohols usually oxidize to
acids. With some care (Usually CrO3)
an aldehyde may be obtained.
[O]
CrO3, py
CH3CH2CH2 OH
[O]
KMnO4
O
CH3CH2CH
Easily oxidized
to acid
O
CH3CH2C OH
13-16
13.6 Redox in Living Systems
Oxidation-gain of oxygen
loss of hydrogen (usually 2)
Reduction-loss of oxygen
gain of hydrogen (usually 2)
More oxidized form
H
R C H
H
H
H
R C OH R C O
H
More reduced form
OH
R C O
13-17
Biological Redox-2
Oxidoreductases catalyze biological
redox reactions. Coenzymes (organic
molecules) are required to donate or
accept hydrogen.
NAD+ is a common coenzyme.
-
COO
COO
H O C H Malate
C O
CH2 dehydrogenase CH
2 COO
COO
+ NADH + H+13-18
+ NAD+
13.7 Phenols
Widely used as health care germicides and
as flavors and preservatives. OH
CH3
OH
OH
CH3CH
CH3
Thymol
(mint)
CH3
p-cresol
in Lysol
HO
CH2
5
CH3
hexyl resorcinol
in throat lozenges
13-19
13.7 Phenols-2
OH
+ NaOH
ONa
+ H2O
Phenols are acidic but not as acidic as
carboxylic acids. They react with NaOH to
give salts and water. (Acid/base chapter.)
Note: alcohols are not acidic in the context of
our class.
13-20
13.8 Ethers
Ethers are slightly polar but do not
hydrogen bond to one another.
Trends in boiling points (Similar MW)
CH3CH2CH3 bp -42
oC
bp -23
oC
CH3O CH3
CH3CH2OH bp +78.5
oC
13-21
Ethers: names
Common names for ethers consist of the
names of the two groups attached to the O
listed in alphabetical order (or size) and
followed by ‘ether’. Each part is a separate
word. Name:
CH3CH2
CH3
O
CH3 CH O CH3
Isopropyl methyl ether
ethyl phenyl ether13-22
Ethers: names-2
The IUPAC names for ethers are based
on the alkane name of the longest
chain attached to the O. The shorter
chain is named as an alkoxy
substituent. (alkane with the ane
replaced by oxy, eg. CH3CH2O=ethoxy)
Thus
CH3CH2CH2CH2CH2-O-CH3
1-methoxypentane
13-23
Ethers: reactions
• Chemically ethers are moderately inert
• Symmetrical ethers may be prepared
by dehydrating two alcohol molecules
CH3 CH2OH
HO CH2 CH3
H+ (H3PO4)
warm
CH3 CH2O CH2 CH3
13-24
Ethers: uses
Ethers are often used as anesthetics.
CH3 CH2O CH2 CH3 Diethyl ether
First successful
general anesthetic
F Cl
CH3O C C H
penthrane
F Cl
13-25
13.9 Thiols: names
Named based on longest alkane chain
with the suffix thiol position indicated
by number. E. g.
CH3
CH3 CH CH2 CH2
SH
3-methy-1-butanethiol
13-26
Thiols/Disulfides: reactions
COOH I (very mild)
2
H C SH
H
H2, Pt
NH2
LiAlH4
cysteine, an
NaBH4
amino acid
2
COOH
COOH
C CH2 S S CH2C H
NH2
NH2
+ 2H
cystine, important
in proteins
The thiol-disulfide redox pair is responsible
for a critical factor in protein structure
called a disulfide bridge.
13-27
The End
Alcohols, etc.
13-28