5. NOMENCALTURE OF ALCOHOL
Common Naming of alcohols:
Number the-longest carbon chain so that the -OH group is
attached to the carbon atom with the lowest possible
number.
Name the parent compound by using the alkane name and
replacing the -e ending with an -ol ending.
Indicate the position of the hydroxyl group with a number
in any alcohol containing three or more carbon atoms.
6. 1. Aliphatic alcohol
i. The parent alcohol - the longest C chain
with OH group attached to it
OH group is given the lowest number in
the chain.
prefix & suffix used if alkyl groups are
exist more than one times
9. ii. When there are two or more –OH
groups present, the name ends with
diol, triol and so on.
OH OH
CH3CHCH2CHCH3 2,4-pentanediol
OH
CH3CCH2OH 1,2,2-propanetriol
OH
10. 2. Aromatic alcohol (phenols)
In most cases, the name phenol is used
as the parent’s name.
OH OH
NO2
CH3
4-methylphenols 3-nitrophenols
(4-methyl hydroxybenzene)
11. Physical Properties of Alcohol:
As the alkane-like alkyl group (hydrophobic @
water hating) becomes larger, water solubility
decrease.
H O H
hydrogen bond
R OH
12. (i) Boiling point
The boiling point of an alcohol is always much higher than
that of the alkane with the same number of carbon atoms.
Intermolecular foces:
Between alkanes, the presence of van der Waals forces.
Between alcohols, the presence of hydrogen bonding
Hydrogen bonding are much stronger than VdW forces
and therefore it takes more energy to separate alcohol
molecules than it does to separate alkane molecules.
Therefore, boiling point of alcohols is higher than
alkanes.
13. • The boiling points of the alcohols increase as the
number of carbon atoms increases.
– Alcohols with lower number of carbons has
smaller size compared to alcohols with higher
number of carbons.
– Alcohols with smaller size will have weaker van
der Waals forces instead of hydrogen bonding that
is formed between OH group.
– Therefore, alcohols with lower number of carbons
have lower boiling points.
14. Volatility
• But they also cause alcohols to have a lower volatility than
alkanes of a similar molecular mass
Solubility
• Alcohols dissolve in water because hydrogen bonds form
between the polar –O-H groups of the alcohols and water
molecules
• The first three members of the homologous series are
soluble in water
• Solubility decreases as the chain length increases; the
larger part of the alcohol molecule is made up of a non-
polar hydrocarbon chain. Also the hydrocarbon part of the
chain doesn’t form hydrogen bonds with water
15. Chemical properties of Alcohols
• As an acid and as a base
- Alcohol can donate or accept a proton
1. Reaction with Sodium (alcohol as acid)
2. Dehydration of alcohols to yield alkenes
(alcohol as basic)
16. 1.Reaction with Sodium (alcohol as acid)
As an acid
R-OH + H2O RO- + H3O+
• Alcohol reacts with Sodium to form sodium
alkoxide and hydrogen gas.
• This reaction shows the acidic properties of
alcohol.
eg: RO-H + Na RO-Na+ + 1/2H2
CH3CH2OH + Na CH3CH2O-Na+ + 1/2H2
(sodium alkoxide)
17. 2.Dehydration of alcohols to yield alkenes
As a base
R-CH2-OH + HA RCH2-OH2 + A-
eg:
CH3-CH2-OH + H2SO4 conc CH2=CH2 + H2O
Refer to the Saytzeff Rule to predict major
alkene product.
18. Saytzeff Rule
• major product is the more stable alkene.
• Which is the more stable alkene?
– the most number of alkyl groups
attached to the C = C
19. Preparation of Alcohol:
(a) Fermentation of Carbohydrates : by yeast
eg:
C6H12O6 2CH3CH2OH + 2CO2
sugar ethanol
This process still widely used to prepare
alcohol
20. (b) Hydration of Alkenes
- Alkenes was added by H2O and H2SO4 / H3PO4.
This reaction follows Markovnikov’s Rule
eg:
R-C=CH2 + H2O / H+ R-C-CH3
Alkene Alcohol
21. Markovnikov Rule:
• In addition of electrophilic to an
alkene, the more positives reagent adds
to the carbon double bond that have
largest number of hydrogen bonded to
it.
22. (c) Hydrolysis of Haloalkanes
- Alkyl Halide react with strong bases (NaOH)
to produce alcohols and Sodium Halides (NaX)
eg:
R-X + OH- R-OH + X-
H2O/reflux
CH3-Br + NaOH CH3-OH + NaBr
23. (d) Addition of Grignard Reagents to Carbonyl
Compounds
- We can use aryl, alkyl and vinylic halides
react with magnesium in ether solution to
generate Grignard reagents, RMgX.
ether
- R-X + Mg RMgX
where R = alkyl/aryl/vinyl
24. • These Grignard reagents react with carbonyl
compounds to yield alcohol.
hydrolysis / H3O+
RMgX + RCHO R2CHOH
Grignard alcohol
reagent
25. Mg / ether
CH3CH2 X CH3CH2 MgBr
O
H2O / H+
H C CH3
carbonyl
OH
CH3CH2CCH3
H
26. (e) Reaction with carboxylic acid to form
an ester (esterification)
general equation: H+
RCOOH + R’OH RCOOR’ + H2O
eg:
CH3COOH + CH3CH2OH CH3COOCH2CH3 + H2O
carboxylic acid alcohol ester water
(etanoic acid) (ethanol)
27. (f) Hydrogenation of Alcohol
• Dehydrate with conc. H2SO4,
• then add H2 - Hydrogenation
OH
H2SO4 H2
CH3CHCH3 CH2 CHCH3 CH3CH2CH3
Pt
alcohol alkene alkane
28. (g) Reaction with Hydrogen Halides, Phosphorus
Halides (PX3 /PX5) and Thionyl Chloride (SOCl2)
- When alcohol react with a hydrogen halide, a
substitution takes place producing alkyl halide and
water.
General reaction:
(i) R - OH + H X R - X + H2O
(ii) 3ROH + PX3 3RX + H3PO3
(iii) ROH + PCl5 RCl + POCl3 + HCl
(iv) ROH + SOCl2 RCl + SO2 + HCl
30. (h) Formation of Tosylate
• Typical acids used for alcohol dehydration are H2SO4
or p-toluenesulfonic acid (TsOH).
• More substituted alcohols dehydrate more
easily, giving rise to the following order of reactivity.
31. Tosylate: A Good Leaving Group
• Alcohols are converted to tosylates by treatment with
p-toluenesulfonyl chloride (TsCl) in the presence of
pyridine.
• This process converts a poor leaving group (¯OH) into a
good one (¯OTs).
• Tosylate is a good leaving group because its conjugate
acid, p-toluenesulfonic acid (CH3C6H4SO3H, TsOH) is a
strong acid (pKa = -7).
32. Tosylate: A Good Leaving Group
• (S)-2-Butanol is converted to its tosylate with
retention of configuration at the stereogenic center.
Thus, the C—O bond of the alcohol is not broken
when tosylate is formed.
33. Tosylate: A Good Leaving Group
• Because alkyl tosylates have good leaving groups, they
undergo both nucleophilic substitution and
elimination, exactly as alkyl halides do.
• Generally, alkyl tosylates are treated with strong nucleophiles
and bases, so the mechanism of substitution is SN2, and the
mechanism of elimination is E2.
34. Tosylate: A Good Leaving Group
• Because substitution occurs via an SN2 mechanism, inversion
of configuration results when the leaving group is bonded to
a stereogenic center.
• We now have another two-step method to convert an alcohol
to a substitution product: reaction of an alcohol with TsCl
and pyridine to form a tosylate (step 1), followed by
nucleophilic attack on the tosylate (step 2).
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35. Tosylate: A Good Leaving Group
• Step 1, formation of the tosylate, proceeds with retention of
configuration at a stereogenic center.
• Step 2 is an SN2 reaction, so it proceeds with inversion of
configuration because the nucleophile attacks from the backside.
• Overall there is a net inversion of configuration at a stereogenic
center.
Example:
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