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ORGANIC CHEMISTRY
General, Organic, and Biochemistry
9th Edition
Katherine J. Denniston
Joseph J. Topping
Danaè R. Quirk Dorr
Robert L. Caret
Copyright © 2017 McGraw-Hill Education. Permission required for reproduction or display
13.1 Structures and Physical Properties
13.1 Structure and Physical Properties
• Aldehydes and ketones are polar compounds
• The carbonyl group is polar
– The oxygen end is electronegative
1
13.1 Structure and Physical
Properties
Hydrogen Bonding in Carbonyls
• Aldehydes and ketones cannot form
intermolecular hydrogen bonds
• However, water can form hydrogen bonds to
them
Physical Properties
Carbonyls boil at
• Higher temperatures than:
– Hydrocarbons
– Ethers
• Lower temperatures than:
– Alcohols
13.2 Nomenclature and Common
Names
2
Naming Aldehydes
• Locate the parent compound
– Longest continuous carbon chain
– Must contain the carbonyl group
• Replace the final –e of the parent with –al
• Number the chain with the carbonyl carbon as 1
• Number and name all substituents
13.2 Nomenclature and
Common Names
Naming Aldehydes
What is the name of this molecule?
1.
2.
3.
4.
Parent chain – 5 carbons = pentane
Change suffix – pentanal
Number from carbonyl end – L to R
Number / name substituents – 2-methyl
5
4
3
2-methylpentanal
2
1
13.2 Nomenclature and
Common Names
Common Names of Aldehydes
• These names are taken from Latin roots as are
the first 5 carboxylic acids
• Greek letters are used to indicate the position of
substituents with the carbon atom adjacent or
bonded to the carbonyl carbon being the a
carbon
13.2 Nomenclature and
Common Names
IUPAC and Common Names With
Formulas for Several Aldehydes
Examples of Ketones
Simplest ketone MUST have 3 carbon atoms so
that the carbonyl group is interior
2
• Base name: longest chain with the C=O
• Replace the –e of alkane name with –one
• Indicate position of C=O by number on chain
so that C=O has lowest possible number
13.2 Nomenclature and
Common Names
IUPAC Naming of Ketones
2
Rules directly analogous to those for aldehydes
• Base name: longest chain with the C=O hept
• Replace the –e of alkane name with –one
• Indicate position of C=O by number on chain
so that C=O has lowest possible number 2
5
4
3
2
1
4-methyl-2-heptanone
13.2 Nomenclature and
Common Names
Common Names of Ketones
• Based on the alkyl groups that are bonded to
the carbonyl carbon
– Alkyl groups are prefixes (2 words) followed by the
word ketone
– Order of alkyl groups in the name
• Alphabetical
• Size – smaller to larger
13.3 Important Aldehydes and Ketones
3
• Methanal (formaldehyde) - gas used in aqueous
solutions as formalin to preserve tissue
• Ethanal (acetaldehyde) - produced from ethanol
in the liver causing hangover symptoms
• Propanone (Acetone) - simplest possible ketone
– Miscible with water
– Flammable
– Both acetone and methyl ethyl ketone (butanone) are
very versatile solvents
13.3 Important Aldehydes
and Ketone
Important Uses of Carbonyl
Compounds
• Used in many industries
– Food chemicals
• Natural food additives
• Artificial additives
– Fragrance chemicals
– Medicines
– Agricultural chemicals
13.3 Important Aldehydes
and Ketone
Vanillin and 2-Octanone
13.3 Important Aldehydes
and Ketone
Benzaldehyde and
Cinnamaldehyde
13.3 Important Aldehydes
and Ketone
Citral and α-Demascone
13.4 Reactions Involving Aldehydes and
Ketones
4
Preparation of aldehydes and ketones
• Principal means of preparation is oxidation of the
corresponding alcohol
– Primary alcohol produces an aldehyde
– Secondary alcohol produces a ketone
– Tertiary alcohol does not oxidize
• This oxidation process removes two hydrogens
13.4 Reactions Involving
Aldehydes and Ketones
1° Alcohol Oxidation
• An aldehyde is formed
4
13.4 Reactions Involving
Aldehydes and Ketones
2° Alcohol Oxidation
• A ketone is formed
4
13.4 Reactions Involving
Aldehydes and Ketones
3° Alcohol
• 3o alcohols cannot undergo
oxidation:
4
13.4 Reactions Involving
Aldehydes and Ketones
Reactions of Aldehydes and
Ketones
1. Oxidation and Reduction
a. Aldehydes: oxidized to carboxylic acids
b. Aldehydes and ketones are reduced to
alcohols: aldehydes to primary alcohols and
ketones to secondary alcohols
2. Addition
a. Alcohols to give hemiacetals and acetals,
13.4 Reactions Involving
Aldehydes and Ketones
Oxidation of Aldehydes
• Aldehydes are easily oxidized to carboxylic
acids by almost any oxidizing agent
5
– So easily oxidized that it is often difficult to prepare
them as they continue on to carboxylic acids
13.4 Reactions Involving
Aldehydes and Ketones
Visually Distinguishing Aldehydes
From Ketones
Visual tests for the aldehyde functional group
based on its easy oxidation are:
• Tollen’s Test
– Silver ion is reduced to silver metal
– Use a basic solution of Ag(NH3)2+
– The silver metal precipitates and coats the container
producing a smooth silver mirror
13.4 Reactions Involving
Aldehydes and Ketones
Tollen’s Test
13.4 Reactions Involving
Aldehydes and Ketones
Benedict’s Test
• Benedict’s Test
– Reagent is a buffered aqueous solution
of Cu(OH)2 and sodium citrate
– Reacts with aldehydes, but not with
ketones
– Cu2+ is reduced to Cu+
• Solution of Cu2+ is a distinctive blue color
• Color fades during the reaction as Cu+
precipitates as the red solid, copper(I)
oxide, Cu2O
13.4 Reactions Involving
Aldehydes and Ketones
Benedict’s Test on Glucose
• Benedict’s Test
13.4 Reactions Involving
Aldehydes and Ketones
Reduction of Carbonyls
7
• Both aldehydes and ketones are readily
reduced to alcohols
– Reduction occurs with hydrogen as the reducing agent
• Classical reaction is hydrogenation
– React with hydrogen gas
– Requires a catalyst – Ni, Pt, Pd
13.4 Reactions Involving
Aldehydes and Ketones
Addition Reactions
7
• Principal reaction is the addition reaction
across the polar C=O double bond
– Very similar to the addition hydrogenation of
alkenes
– Requires catalytic acid in the solution
• Product of the reaction is a hemiacetal
– Hemiacetals are quite reactive
– Undergo a substitution reaction with the –OH
group of the hemiacetal is exchanged for another
–OR group from the alcohol
– Reaction product is an acetal
– This reaction is reversible
13.4 Reactions Involving
Aldehydes and Ketones
Hemiacetal and Acetal Formation
Generalized structure
of a hemiacetal
7
Generalized structure
of an acetal
13.4 Reactions Involving
Aldehydes and Ketones
Aldehyde and Alcohol Reaction
• Product of the addition reaction is a
hemiacetal followed by formation of an acetal
13.4 Reactions Involving
Aldehydes and Ketones
Ketone and Alcohol Reaction
13.4 Reactions Involving
Aldehydes and Ketones
Intramolecular Hemiacetal
Formation
• The aldehyde and alcohol functional groups
can both be parts of the same molecule in an
intramolecular reaction
13.4 Reactions Involving
Aldehydes and Ketones
Hemiacetals and Carbohydrates
• This reaction is important in the chemistry of
carbohydrates, where hemiacetals are readily
formed:
13.4 Reactions Involving
Aldehydes and Ketones
Acetals and Carbohydrates
• The acetal is formed between the hemiacetal
hydroxyl group in blue with the alcohol
hydroxyl group in red on a second molecule
13.4 Reactions Involving
Aldehydes and Ketones
Keto-Enol Tautomers
8
• Tautomers are isomers which differ in the
placement of:
– A hydrogen atom
– A double bond
– The keto form has a C=O while the enol form has a
C=C.
• The keto form is usually the most stable
Reaction Schematic
Summary of Aldehyde and
Ketone Reactions
1. Aldehydes and ketones
a. Oxidation of an aldehyde
b. Reduction of aldehydes and ketones
c. Addition reactions
i.
ii.
Hemiacetal and acetal
Cyclic Hemiactetal and acetal
2. Keto-enol tautomerization
Summary of Reaction Equations