![]() They are employed in the paper, plastic, and rubber industries. Amides are used as coloring agents in crayons, pencils, and ink. The amide group forms is extremely important in biological systems, where it is called a “peptide”, used for linking amino acids together to form polypeptides and (ultimately) proteins. Anesthetics such as procaine and benzocaine also contain esters. Esters are employed in the manufacture of fabrics (polyesters) and Plexiglass. This ester also serves as an alarm signal for honeybees. Propyl acetate contributes to the odor of pears, while isoamyl acetate gives bananas their smell. Some esters have very pleasant odors, so they are used in the manufacture of many perfumes. With the exception of acid chlorides and acid anhydrides, the carboxylic acid derivatives are very common in biological molecules and/or metabolic pathways.Įsters are very important in synthesis and in nature. Other derivatives are carboxylic esters (usually just called ‘esters’), thioesters, amides, acyl phosphates, acid chlorides, and acid anhydrides. For example, citric acid (three carboxyl groups) is especially abundant in citrus fruits and it used as a flavoring and preservative in many foods and beverages. Some compounds contain multiple carboxylic acids within a single molecule. Carboxylic acids with longer carbon chains (fatty acids) are used by animals as a way of storing energy and are widely used in the manufacture of soaps. Acetic acid gives vinegar its characteristic smell and flavor and is a fundamental biological and industrial building block. Formic acid acts as a protective chemical for many stinging insects and plants. A carboxylate ion (see figure below), in which the negative charge is spread over two different oxygen atoms through resonance structures, is more stable than an isolated oxygen-centered anion.Ĭarboxylic acids are used in a variety of environments. ![]() because of the relative stability of the resulting anion. For example, ethanol \left( \ce group that is directly connected to a carbonyl will ionize to a small extent when dissolved in water. We are already familiar with several common alcohols. The distinction is important, because as we will see later, there is a significant difference in the reactivity of alcohols and phenols. We will learn more about the structure and reactions of aromatic groups next semester. Aromatic groups are planar (flat) ring structures, and are widespread in nature. ![]() The aromatic group is exemplified by benzene (which used to be a commonly used solvent in the organic lab, but which was shown to be carcinogenic), and naphthalene, a compound with a distinctive ‘mothball’ smell. The double and triple-bonded carbons in alkenes and alkynes have fewer hydrogen atoms bonded to them – they are thus referred to as unsaturated hydrocarbons. Alkanes are said to be saturated hydrocarbons, because the carbons are bonded to the maximum possible number of hydrogens – in other words, they are saturated with hydrogen atoms. We will have more to say about the subject of cis and trans alkenes in chapter 3, and we will learn much more about the reactivity of alkenes in chapter 10.Īlkanes, alkenes, and alkynes are all classified as hydrocarbons, because they are composed solely of carbon and hydrogen atoms. In the example below, the difference between cis and trans alkenes is readily apparent. The cis and trans forms of a given alkene are different molecules with different physical properties because, as we will learn in chapter 2, there is a very high energy barrier to rotation about a double bond. Furthermore, many alkenes can take two geometric forms: cis or trans. * Presentation mode is only available to teachers with an active Dashboard license.Later, we will study the nature of the bonding on alkenes and alkynes, and learn that that the bonding in alkenes is trigonal planar in in alkynes is linear.
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