Aldehydes and Ketones
Aldehydes and ketones are organic compounds that contain a carbonyl group, which is a carbon atom double-bonded to an oxygen atom. Aldehydes have the carbonyl group at the end of a carbon chain, while ketones have it within the chain. They are important in organic synthesis and are used in various industrial processes, including the production of plastics and pharmaceuticals.
5 Key excerpts on "Aldehydes and Ketones"
eBook - ePubHandbook of Environmental Analysis
Chemical Pollutants in Air, Water, Soil, and Solid Wastes, Third Edition
- Pradyot Patnaik(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
...16 Aldehydes and Ketones Aldehydes and Ketones constitute an important class of organic compounds containing the carbonyl group. An aldehyde has the structure RCH(= O) while a ketone has the structure R 2 C(= O). where R may be an alkyl, alkenyl, alkynyl, or aryl group. In aldehyde, one hydrogen atom is attached to the carbonyl group, while in ketone no hydrogen is bound to the carbonyl group. In formaldehyde, two hydrogen atoms are bound to the carbonyl group. Thus, Aldehydes and Ketones are compounds of closely related classes exhibiting many similar chemical properties. Low molecular weight Aldehydes and Ketones are used in the manufacture of resins, dyes, esters, and other organic chemicals. Many ketones including acetone and methyl ethyl ketone (MEK) are industrial solvents. Some of the compounds that are used commercially are presented in Table 16.1. Many Aldehydes and Ketones are emitted into the atmosphere from chemical and combustion processes. The photochemical degradation of many organic substances also generates lower Aldehydes and Ketones. Table 16.1 Some Commercially Used Aldehydes and Ketones CAS No. Compounds Synonyms Aldehydes [75-07-0] Acetaldehyde Ethanal [107-02-8] Acrolein 2-Propenal [100-52-7] Benzaldehyde Benzoic aldehyde [123-72-8] Butyraldehyde Butanal [104-55-2] Cinnamaldehyde 3-Phenyl-2-propenal [123-73-9] Crotonaldehyde 2-Butenal [112-31-2] Decyl...
eBook - ePub- J Fisher, J.R.P. Arnold, Julie Fisher, John Arnold(Authors)
- 2020(Publication Date)
- Taylor & Francis(Publisher)
...Alcohols and Aldehydes and Ketones have oxygen atoms with lone pairs of electrons available for donation in a hydrogen bonding interaction (Section H1). However, neither aldehydes nor ketones have groups that may act as hydrogen bond acceptors. If an aldehyde or ketone was to be placed in solution with molecules that can act as hydrogen bond acceptors, then a network of such bonds is established. This ability to hydrogen bond in solution, coupled with the intrinsic polar nature of the carbonyl bond, means that many of the low molecular weight Aldehydes and Ketones are soluble in water. Oxidation reactions The differing behavior of Aldehydes and Ketones in oxidizing conditions is the main reason for these compounds being classified separately. Aldehydes are readily oxidized to carboxylic acids; Indeed the reaction is generally so favorable that a sample of aldehyde will generally contain a significant amount of the acid if it has been left standing in air for long periods of time. Anumber of chemical tests for the presence of aldehydes have been developed that depend on their ease of oxidation (Figure 1). Of particular significance to biologists, Benedict's test is often used clinically to establish the presence of glucose in urine samples, a common occurrence with diabetes (Figure 1b). Under normal conditions ketones are not susceptible to oxidation. Under very forcing conditions in the laboratory it is possible to oxidize ketones (RCOR′) to produce two carboxylic acid molecules (RCOOH and R′COOH). Figure 1 Oxidation of aldehydes using (a) Tollen's and (b) Benedict's reagent. Reduction reactions The reduction reactions of Aldehydes and Ketones are the reverse of the oxidation reactions of alcohols (Section J1)...
eBook - ePub- Katarzyna Staszak, Karolina Wieszczycka, Bartosz Tylkowski, Katarzyna Staszak, Karolina Wieszczycka, Bartosz Tylkowski(Authors)
- 2020(Publication Date)
- De Gruyter(Publisher)
...Both atoms forming such a double bond are characterized by hybridization of the sp 2 type. Spatially, these two atoms and two other atoms directly related to the carbon atom lie in the same plane. One of the carbon–oxygen bonds is of σ type, formed by two overlapping sp 2 orbital bonds, while the other is of π type, realized through the commonalization of non-hybridized electrons from orbital π. The carbonyl group “–C=O” is a common element in the structure of Aldehydes and Ketones and to a large extent determines their chemical properties. Aldehydes are organic compounds in which the carbonyl group is connected by one single bond to the hydrogen atom and the other to the rest of the hydrocarbon molecule. In aldehydes, the C=O group occurs at the end of the carbon chain; it is connected with a single C–C bond, and the fourth bond is saturated with hydrogen atom. Ketones are organic compounds containing a carbonyl group which is combined with two hydrocarbon groups. In ketones, the C=O group occurs within the carbon chain of molecules; the carbon atom of the carbonyl group is secondary. Ethers are organic compounds in which C–O–C bonds are present, where none of the carbon atoms is bound to more than one oxygen atom [ 1, 2 ]. 5.2 Aldehydes and Ketones 5.2.1 Nomenclature Aldehydes are carbonyl compounds in which carbonyl carbon is bonded to two hydrogen atoms (HC(=O)H) or to a hydrogen atom and carbon atom of the hydrocarbon substituent R–(RC(=O)H). The acyclic (chain) aldehyde names are formed by adding the suffix -al (for monoaldehyde) or -dial (for dialdehyde) to the hydrocarbon name...
eBook - ePub- Graham Patrick(Author)
- 2004(Publication Date)
- Taylor & Francis(Publisher)
...The substituents attached to the carbonyl group determine whether it is an aldehyde or a ketone, and whether it is aliphatic or aromatic (Sections C1 and C2). The geometry of the carbonyl group is planar with bond angles of 120° (Section A4 ; Figure 1). The carbon and oxygen atoms of the carbonyl group are sp 2 hybridized and the double bond between the atoms is made up of a strong σ bond and a weaker π bond. The carbonyl bond is shorter than a C–O single bond (1.22 Å vs. 1.43 Å) and is also stronger since two bonds are present as opposed to one (732 kJ mol −1 vs. 385 kJ mol −1). The carbonyl group is more reactive than a C–O single bond due to the relatively weak π bond. The carbonyl group is polarized such that the oxygen is slightly negative and the carbon is slightly positive. Both the polarity of the carbonyl group and the presence of the weak π bond explains much of the chemistry and the physical properties of Aldehydes and Ketones. The polarity of the bond also means that the carbonyl group has a dipole moment. Figure 1. Geometry of the carbonyl group. Properties Due to the polar nature of the carbonyl group, Aldehydes and Ketones have higher boiling points than alkanes of similar molecular weight. However, hydrogen bonding is not possible between carbonyl groups and so Aldehydes and Ketones have lower boiling points than alcohols or carboxylic acids. Low molecular weight Aldehydes and Ketones (e.g. formaldehyde and acetone) are soluble in water. This is because the oxygen of the carbonyl group can participate in intermolecular hydrogen bonding with water molecules (Section C3; Figure 2). As molecular weight increases, the hydrophobic character of the attached alkyl chains starts to outweigh the water solubility of the carbonyl group with the result that large molecular weight Aldehydes and Ketones are insoluble in water. Aromatic ketones and aldehydes are insoluble in water due to the hydrophobic aromatic ring. Figure 2...
eBook - ePubChemistry
Concepts and Problems, A Self-Teaching Guide
- Richard Post, Chad Snyder, Clifford C. Houk(Authors)
- 2020(Publication Date)
- Jossey-Bass(Publisher)
...These are known as ethers. Ethers have been used in chemical reactions and in medicine. The simplest ether has two methyl groups connected by an oxygen atom. This compound is known as dimethyl ether. Below are the molecular formula, the condensed formula, the dashed formula, and the bond-line structure for dimethyl ether. Are ethanol and dimethyl ether structural isomers? Why or why not? Answer: Yes, because ethanol and dimethyl ether have the molecular formula C 2 H 6 O but different molecular structures. CARBONYL GROUPS Some carbon atoms are connected to oxygen atoms through double bonds. The C=O group is known as the carbonyl group and is common to several larger functional groups. In particular, the carbonyl group is part of the aldehyde and ketone functional groups. The simplest functional groups that contain these are known as the aldehyde and the ketone (shown below). The aldehyde and ketone are similar but there is a slight structural difference between the two. Both possess the C=O bond (the carbonyl group) but the aldehyde has a hydrogen atom bonded to the C=O carbon. The ketone has the basic structure C–C(=O)–C. The (=O) implies this bond is connected to the carbon to its left. A ketone is a C=O carbon connected to two other carbons through the C=O carbon. Ethanal is the simplest aldehyde having the basic structure –C(=O)–H while propanone, the simplest ketone, has its C=O flanked by two alkyl groups. In this case, propanone's C=O carbon is bonded to two methyl groups. So far you have seen the alcohol, ether, ketone, and aldehyde functional groups. Circle and label the functional groups found in the following organic compounds. Answer: The next two oxygen-containing functional groups have the carbonyl group with its carbon also connected to one other oxygen atom through a single bond. This oxygen atom is an sp 3 hybridized oxygen atom. The R in the formulas below represent any alkyl group...
