Title: Structures of Alcohols, Phenols, Thiols and Ethers
1Structures of Alcohols, Phenols, Thiols and Ethers
- Alcohols, phenols, thiols and ethers consist of a
hydrocarbon singly bonded to an oxygen or a
sulfur - Alcohols have an -OH group attached to an alkane,
phenols have an -OH group attached to a benzene,
thiols have an -SH group attached to an alkane
and ethers have an O bonded to two Cs
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3Naming Alcohols
- Parent name ends in -ol
- Find longest chain containing the C to which the
OH group is attached - Number Cs starting at end nearest OH group
- Locate and number substituents and give full name
- - use a number to indicate position of OH group
- - cyclic alcohols have cyclo- before the parent
name numbering begins at the OH group, going in
direction that gives substituents lowest possible
numbers - - use a prefix (di-, tri-) to indicate multiple
OH groups in a compound
4Nomenclature
5Classification of Alcohols
- Alcohols can be classified as methyl, primary,
secondary or tertiary - Classification is based on the number of alkyl
groups attached to the carbon to which the OH
group is attached - If OH is attached to a 1? C, its a 1? alcohol,
etc.
6Naming Phenols
- Phenol is the common name for an OH group
attached to a benzene, and is accepted by IUPAC - Compounds with additional substituents are named
as substituted phenols - Ortho, meta and para are used when there is only
one other substituent - If there are two or more additional substituents,
each must be numbered, beginning at the OH and
going in direction that gives substituents lowest
numbers (or alphabetical if same in both
directions)
7Many phenols have pleasant odors, and some are
bioactive - Euganol (from cloves) is a topical
anesthetic - Thymol (from thyme) is an antiseptic
8Naming Thiols
- Parent name ends in -thiol
- Find longest chain containing the C to which the
SH group is attached - Number Cs starting at end nearest SH group
- Parent name is alkane name of carbon portion of
longest chain, followed by thiol - Locate and number substituents and give full name
- - use a number to indicate position of SH group
- - cyclic thiols have cyclo- before the parent
name numbering begins at the SH group, going in
direction that gives substituents lowest possible
numbers - - use a prefix (di-, tri-) to indicate multiple
SH groups in a compound
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10Thiols - Nomenclature
- Common names for simple thiols are derived by
naming the alkyl group bonded to -SH and adding
the word "mercaptan"
11Naming Ethers
- Simple ethers are named by their common names
- For common names name each alkyl group attached
to the oxygen followed by ether - For complex ethers IUPAC names are used
- For IUPAC names
- 1. Name as an alkane, with larger alkyl group
being the parent chain - 2. The smaller alkyl group and the O are named
together as an alkoxy group (replace -yl with
-oxy) - 3. Number chain starting at end nearest alkoxy
group - 4. Use a number to give location of alkoxy group
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13Naming Cyclic Ethers
- Cyclic ethers are generally named by their common
names (we will not study the IUPAC names) - A cyclic ether containing two carbons is called
ethylene oxide (generally known as epoxides) - A cyclic ether containing 4 carbons (with 2
double bonds) is called a furan - A cyclic ether containing 5 carbons (with 2
double bonds) is called a pyran - A cyclic ether containing 4 carbons and 2 oxygens
is called a dioxane
14Naming Examples
15Physical Properties of Alcohols, Phenols, Thiols
and Ethers
- All of these types of compounds have a bent
geometry around the O or the S, and are polar
compounds - Alcohols and phenols contain a very polarized O-H
bond, and they can H-bond with themselves and
with other alcohols or water - - Small alcohols (4 or less Cs) are soluble in
water - - Phenol is soluble in water (even with 6 Cs)
because it partially ionizes in water (its a
weak acid) - - Alcohols and phenols have relatively high
boiling points - Thiols are much less polar than alcohols because
the electronegativity of S is the same as that of
C (2.5), much less than that of O (3.5), so C-S
and S-H bonds are not polar - - thiols do not H-bond and have relatively low
boiling points - Ethers do not H-bond with themselves, so have
boiling points similar to hydrocarbons - -ethers are only slightly soluble in water and
are highly flammable
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18Physical Properties
- bp increases as MW increases
- solubility in water decreases as MW increases
19Acidity and Basicity of Alcohols and Phenols
- Alcohols and phenols, like water, can act as
either weak acids or weak bases (although phenol
is more acidic) - Phenols are more acidic because the anion that
forms upon loss of the proton is stabilized by
resonance
20Combustion Reactions of Alcohols and Ethers
- Both alcohols and ethers can burn with oxygen to
produce water, carbon dioxide and heat (just like
hydrocarbons) - However, ethers are much more flammable than
alcohols and care should be taken when working
with ethers in the laboratory (just a spark from
static electricity can set off ether fumes) - Examples
- CH3CH2OH 3O2 ? 2CO2 3H2O
Heat - CH3-O-CH3 3O2 ? 2CO2 3H2O
Heat
21Dehydration of Alcohols to Form Alkenes
- An alcohol can lose a water molecule to form an
alkene using an acid catalyst such as H2SO4 and
heat (an elimination reaction) - This is the reverse of the addition of H2O to an
alkene - Dehydration is favored by using heat (endothermic
reaction) and a solvent other than water (lower
concentration of H2O) - When more than one alkene can be formed,
Zaitsevs rule states that the more substituted
alkene will be the major product - Order of reactivity 3? gt 2? gt (1? gt
methyl) - - In fact this reaction only works with 3? and
2? alcohols
22Mechanism of Acid-Catalyzed Dehydration of an
Alcohol
- First, the acid catalyst protonates the alcohol
- Next, H2O is eliminated to form a carbocation
- Finally, a proton is removed to form an alkene
H3O