Chemistry
Physical Properties of Aldehydes and Ketones
Aldehydes and ketones have distinct physical properties. Aldehydes with fewer than five carbon atoms are typically colorless liquids with a pungent odor, while ketones are often colorless liquids with a pleasant smell. Both aldehydes and ketones have lower boiling points compared to alcohols and carboxylic acids of similar molecular weight due to their inability to form hydrogen bonds with themselves.
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eBook - ePubDAT Prep Plus 2023-2024
2 Practice Tests + Proven Strategies + Online
- (Author)
- 2023(Publication Date)
- Kaplan Test Prep(Publisher)
The location of the carbonyl group must be specified with a number, except in cyclic ketones, where it is assumed to occupy the number 1 position. The common system of naming ketones lists the two alkyl groups followed by the word ketone. When it is necessary to name the carbonyl as a substituent, the prefix oxo- is used. Figure 46.3 Physical Properties The Physical Properties of Aldehydes and Ketones are governed by the presence of the carbonyl group and its strong dipole moment. Due to differences in electronegativity, the carbon carries a strong partial positive charge, and the oxygen carries a strong partial negative charge. The dipole moments associated with the polar carbonyl groups of nearby molecules align, causing an elevation in boiling point of aldehydes and ketones relative to similar alkanes. However, aldehydes and ketones show lower boiling points than comparable alcohols because -OH groups can form hydrogen bonds, but carbonyls cannot. Figure 46.4 Overview of Aldehydes and Ketones Aldehydes and ketones are midway along the oxidation-reduction continuum (shown below). The carbonyl carbon has two bonds to oxygen, placing it between the single C–O bond of alcohols and the three carbon-oxygen bonds of the carboxyl group. Table 46.1 There are numerous methods of preparing aldehydes and ketones, but three are of particular interest: oxidation of alcohols, oxidative cleavage of alkenes, and Friedel-Crafts acylation of benzenes. These three mechanisms are important to study both as synthetic pathways of aldehydes and ketones and also as reaction pathways for other compounds. The reactions of aldehydes and ketones are likewise interrelated with those of other compounds and are often driven by the dipole moment of the carbon-oxygen double bond. Aldehydes and ketones can be oxidized or reduced to form carboxylic acids or alcohols, respectively. They can act as either the nucleophile or substrate in S N 1 and S N 2-type reactions
eBook - ePub- Robert J. Ouellette, J. David Rawn(Authors)
- 2015(Publication Date)
- Elsevier(Publisher)
Table 10.1 ) because of dipole-dipole intermolecular forces due to the carbonyl group. However, alcohols have higher boiling points than aldehydes and ketones even though alcohols have smaller dipole moments than carbonyl compounds. This order of boiling points is the result of hydrogen bonding in alcohols that is not possible in carbonyl compounds. As the molecular weights of the carbonyl compounds increase, their dipole-dipole attractive forces become less important than the London forces of the hydrocarbon skeleton. As a result, the Physical Properties of Aldehydes and Ketones become more like those of hydrocarbons as chain length increases. The boiling point differences become smaller, although the order of boiling points is still alcohol > carbonyl compound > alkane.Solubility of Aldehydes and Ketones in Water
Aldehydes and ketones cannot form hydrogen bonds with one another because they cannot function as hydrogen bond donors. However, the carbonyl oxygen atom has lone pair electrons that can serve as hydrogen bond acceptors. Thus, carbonyl groups can form hydrogen bonds with water. Hence, the lower molecular weight compounds formaldehyde, acetaldehyde, and acetone are soluble in water in all proportions.However, the solubility of carbonyl compounds in water decreases as the chain length increases, and their solubilities become more like those of hydrocarbons. Both acetone and 2-butanone (known in industry as methyl ethyl ketone, or MEK) are excellent solvents for many organic compounds. These polar solvents dissolve polar solutes because “like dissolves like.” These solvents also readily dissolve protic solutes such as alcohols and carboxylic acids because the carbonyl group acts as a hydrogen bond acceptor for these compounds, as shown in the molecular model of acetone hydrogen bonded to methanol, below.10.4 Oxidation-Reduction Reactions of Carbonyl Compounds
The carbonyl group is in an oxidation state between that of an alcohol and a carboxylic acid. Thus, a carbonyl group can be reduced to an alcohol or oxidized to a carboxylic acid.
eBook - PDFChemistry for Today
General, Organic, and Biochemistry
- Spencer Seager, Michael Slabaugh, Maren Hansen, , Spencer Seager, Spencer Seager, Michael Slabaugh, Maren Hansen(Authors)
- 2021(Publication Date)
- Cengage Learning EMEA(Publisher)
c. In cyclic ketones, the carbonyl carbon will always be at position 1, and so the number is omitted from the name: CH 3 O 1 2 The correct name is 2-methylcyclohexanone. ✔ LEARNING CHECK 14.2 Give IUPAC names to the following ketones: a. CH 3 CHCH 2 CHCH 2 O C CH 3 Br Br b. CH 3 O CH 3 14.2 Physical Properties Learning Objective 3 Compare the Physical Properties of Aldehydes and Ketones with those of compounds in other classes. The Physical Properties of Aldehydes and Ketones can be explained by an examination of their structures. First, the lack of a hydrogen on the oxygen prevents the formation of hydrogen bonds between molecules: O C R9 R O C no H attached to the oxygen H R FIGURE 14.3 The ending -dione in butanedione correctly implies there are two ketone groups in its structure. Butanedione gives rise to the pleasant odor of melted butter. iStock.com/bhofack2 Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Aldehydes and Ketones 451 Therefore, boiling points of pure aldehydes and ketones are expected to be lower than those of alcohols with similar molecular weights. Remember, alcohols can form hydrogen bonds with one another. Table 14.2 shows that the boiling points of propanal and acetone are 49°C and 56°C, respectively, whereas the alcohol of comparable molecular weight, 1-propanol, has a boiling point of 97°C.
- Paulo Costa, Ronaldo Pilli, Sergio Pinheiro, Peter Bakuzis(Authors)
- 2022(Publication Date)
- Royal Society of Chemistry(Publisher)
1 Aldehydes, Ketones, Imines and NitrilesThis chapter introduces the reader to some of the concepts that will be used and discussed in more detail throughout the book. It begins with a brief mention of some of the compounds that contain aldehyde, ketone, imine, or nitrile groups that are produced at large or small scales by the chemical industry or are present in natural products with biological activity. This is followed by a description of the three-dimensional structures of the very simplest representatives of each functional group. Their configuration is then analyzed by both valence bond (VB) and simple molecular orbital (MO) approaches. This lays the framework for explaining some physical properties, such as dipole–dipole interactions, boiling and melting points, etc. More importantly, by stressing the relative size of the atomic coefficients of the HOMOs and LUMOs, the electrophilic nature of the carbon in each of the functional groups and the ability of the heteroatom to interact with Brønsted and Lewis acids is predicted. This is done from a historical perspective, which includes biographical sketches of some of those responsible for the development of our understanding of the structures of organic compounds.
Key Concepts
- Structural properties (bond lengths and bond angles) and three-dimensional structures for aldehydes, ketones, imines, and nitriles- Aldehydes, ketones, imines, and nitriles in natural products, drugs, and industrial chemicals- Correlation of dipole moment and physical properties (melting point, boiling point, solubility)- Structural description by valence bond (VB) and molecular orbital (MO) theories set the stage for discussions of their chemical reactivity1.1 Sources and Uses
In this section, we will focus on the C=O, C=N, and C≡N functional groups present in the structure of natural products and some synthetic products of industrial relevance.Formaldehyde, the simplest carbonyl compound, is produced by methanol oxidation. In addition to its use in the preservation of biological species, a large amount of formalin (37% aqueous solution of formaldehyde) is produced for the plastic and resin industries, e.g. for the production of Bakelite® , a urea-formaldehyde resin, and other polymers.Acetaldehyde produced by the palladium-catalyzed ethylene oxidation (Wacker oxidation) is mainly used in the production of pharmaceutical compounds and polymers.Acetone (propanone) is produced by the oxidative cleavage of cumene (isopropyl benzene) and is, by far, the most important commercially available ketone. Together with butanone, they are industrial solvents with low toxicity and are easily distilled off due to their low boiling points. Acetone is also used as a solvent in enamels, paints, and varnishes and is an important raw material in the production of methacrylates and bisphenol.While formaldehyde and acetaldehyde are gases with irritating odors, some of their higher homologs have pleasant and varied smells: butyraldehyde (butter smell), heptanal (green-herbal odor), octanal (orange smell), nonanal (rose smell), citral and neral (citrus scent) are highly valued products in the perfume industry (Figure 1.1
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
Associated with every functional group are characteristic reactions. Aldehydes undergo both oxidation and reduction reactions; ketones undergo reduction reactions. The carbon atom in the carbonyl group also has a double bond. What kind of reactivity does this suggest for aldehydes and ketones? This question can be answered by reviewing the chemistry of the alkenes in Chapter 20. Like alkenes, the aldehydes and ketones have a carbon KEY TERMS Tollens test Fehling and Benedict tests hemiacetal hemiketal acetal ketal cyanohydrin aldol condensation C H O benzaldehyde (oil of bitter almonds) CH 3 O C CH 2 CH 3 carvone (chief component of spearmint oil) CH 2 CH 2 CH 2 CH 2 CH 2 CHCH 2 C O CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 muscone (gland of male musk deer, used in perfume) CHCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 C O CHCH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 civetone (secretion of the civet cat, used in perfume) H 3 C H 3 C OH O C O CH 2 OH CH 3 H 3 C CH 3 O camphor (from the camphor tree) cortisone (hormone; regulation of carbohydrate and protein metabolism; used to reduce inflammation) OH CH 2 OH CH OH CH OH CH OH CH H C O glucose (sugar) OH CH 2 OH CH OH CH OH CH H C O ribose (sugar) OH CH 2 O C OH CH OH CH fructose (sugar) OH CH OH CH 2 CH 3 C CHCH 2 CH 2 C O citral (oil of lemon) CHC H CH 3 CH 3 CH 3 O O CH 2 CH C CH 2 CH 2 CH 2 CH CH 3 CH 3 3 vitamin K 1 (antihemorrhagic vitamin) O CH 3 cinnamaldehyde (oil of cinnamon) CH CH O C H Figure 23.1 Selected naturally occurring aldehydes and ketones. LEARNING OBJECTIVE Science Photo Library/Science Source Images 23.4 • Chemical Properties of Aldehydes and Ketones 581 atom that is bonded to three other atoms—one fewer than the usual maximum four. Such a carbon atom can easily bond to one more atom. Alkenes readily undergo addition reactions. This suggests that the aldehydes and ketones also undergo addition reactions. In fact, addition is the characteristic reaction of aldehydes and ketones.
eBook - PDF- Allan Blackman, Steven E. Bottle, Siegbert Schmid, Mauro Mocerino, Uta Wille(Authors)
- 2022(Publication Date)
- Wiley(Publisher)
Low-molar-mass aldehydes and ketones are more soluble in water than non-polar compounds of similar molar mass because carbonyl groups interact with water molecules by hydrogen bonding. The carbonyl group is a hydrogen bond acceptor (the oxygen atom provides the electrons to form the hydrogen bond with water), as shown. O H O H Table 21.3 lists the boiling points and solubilities of several low-molar-mass aldehydes and ketones in water. TABLE 21.3 Physical properties of selected aldehydes and ketones IUPAC name Common name Structural formula Boiling point (°C) Solubility (g/100 g water) methanal formaldehyde HCHO −21 infnite ethanal acetaldehyde CH 3 CHO 20 infnite propanal propionaldehyde CH 3 CH 2 CHO 49 16 butanal butyraldehyde CH 3 CH 2 CH 2 CHO 76 7 hexanal caproaldehyde CH 3 (CH 2 ) 4 CHO 129 slight propanone acetone CH 3 COCH 3 56 infnite butanone methyl ethyl ketone CH 3 COCH 2 CH 3 80 26 pentan-3-one diethyl ketone CH 3 CH 2 COCH 2 CH 3 101 5 Pdf_Folio:1105 CHAPTER 21 Aldehydes and ketones 1105 CHEMICAL CONNECTIONS Perfumes and fragrances Just about everyone uses some sort of fragrance — as a perfume, a cologne, after-shave, deodorant etc. Fragrances are also widely used in most cleaning agents, including soaps, shampoos and dishwashing liq- uids. Consequently, perfumes and fragrances make up a multibillion dol- lar per year industry. Although perfumes have been used since ancient times, their widespread use has occurred only in the last 150 years, due to the increased availability of odorous compounds, principally through advances in synthetic chemistry. Today, synthetic chemicals are used extensively in the fragrance industry; of the estimated 3000 fragrance ingredients available, only about 5% come directly from natural sources. Perfumes are composed of a mixture of compounds designed to produce a pleasant odour that evolves over many hours. Most perfumes consist of three ‘notes’: head, heart and base.
eBook - ePub- James G. Speight(Author)
- 2019(Publication Date)
- Gulf Professional Publishing(Publisher)
Aromatic hydrocarbon derivatives are derived from benzene. Group members have six free valence electrons which are distributed in a circle in the form of a charged cloud. Because of the presence of these valence electrons, we can predict that the reactivity of these aromatic compounds will be similar to other unsaturated hydrocarbon derivatives. However, benzene is much less reactive than other unsaturated hydrocarbon derivatives. Only at high temperatures and in the presence of a catalyst can benzene take on another hydrogen atom. When it does, cyclohexane is the resultant product.5. Physical properties
Physical properties can be observed or measured without changing the composition of matter. Physical properties are used to observe and describe matter (Howard and Meylan, 1997 ; Yaws, 1999 ). The three states of matter are: solid, liquid, and gas. The melting point and boiling point are related to changes of the state of matter. All matter may exist in any of three physical states of matter. A physical change takes place without any changes in molecular composition. The same element or compound is present before and after the change. The same molecule is present throughout the changes. Physical changes are related to physical properties since some changes require a change in the three-dimensional structure of the molecule.Physical properties that are of interest in the current context include: (i) boiling point, (ii) density and specific gravity, (iii) dew point, (iv) flash point and ignition temperature, (v) melting point, and (vi) vapor density. These properties are listed in alphabetical order rather than attempt to assign importance to any individual property. The properties present indications the behavior of hydrocarbon derives as determined by application of standard test method (Speight, 2015 ).The physical properties of alkene derivatives are similar to those of the alkane derivatives. The boiling points of straight-chain alkenes increase with increasing molar mass, just as with alkanes. For molecules with the same number of carbon atoms and the same general shape, the boiling points usually differ only slightly, just as would be expected for chemicals in which whose molar mass differs by only one to two hydrogen atoms (i.e., RCH2 CHCH2 compared to RCH2 CH2 CH3
eBook - PDF- H. Stephen Stoker(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
128 Santokh Kochar/PhotoDisc/Getty Images Chapter Outline Benzaldehyde is the main flavor component in almonds. Aldehydes and ketones are responsible for the odor and taste of numerous nuts and spices. Aldehydes and Ketones 4 T his is the second of three chapters that consider hydrocarbon deriva-tives that contain the element oxygen. The hydrocarbon derivatives con-sidered in the previous chapter, alcohols and ethers, have the common structural feature of carbon–oxygen single bonds. In this chapter, aldehydes and ketones, the simplest types of hydrocarbon derivatives that contain a carbon–oxygen double bond, are considered. 4-1 The Carbonyl Group L E A R N I N G F O C U S Be able to describe the structural characteristics of a carbonyl group. Both aldehydes and ketones contain a carbonyl functional group. A carbonyl group is a carbon atom double-bonded to an oxygen atom. The structural rep-resentation for a carbonyl group is O S O C P G D Carbonyl group 4-1 The Carbonyl Group 128 4-2 Compounds Containing a Carbonyl Group 129 4-3 The Aldehyde and Ketone Functional Groups 131 4-4 Nomenclature for Aldehydes 132 4-5 Nomenclature for Ketones 134 4-6 Isomerism for Aldehydes and Ketones 136 4-7 Selected Common Aldehydes and Ketones 137 4-8 Physical Properties of Aldehydes and Ketones 141 4-9 Preparation of Aldehydes and Ketones 142 4-10 Oxidation and Reduction of Aldehydes and Ketones 144 4-11 Reaction of Aldehydes and Ketones with Alcohols 148 4-12 Sulfur-Containing Carbonyl Groups 153 Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.
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