{"id":7863,"date":"2021-06-08T21:57:58","date_gmt":"2021-06-08T21:57:58","guid":{"rendered":"https:\/\/opentextbc.ca\/introductorychemistry\/chapter\/other-oxygen-containing-functional-groups\/"},"modified":"2021-10-13T17:54:16","modified_gmt":"2021-10-13T17:54:16","slug":"other-oxygen-containing-functional-groups","status":"publish","type":"chapter","link":"https:\/\/opentextbc.ca\/introductorychemistry\/chapter\/other-oxygen-containing-functional-groups\/","title":{"raw":"Other Oxygen-Containing Functional Groups","rendered":"Other Oxygen-Containing Functional Groups"},"content":{"raw":"[latexpage]\r\n
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Learning Objectives<\/p>\r\n\r\n<\/header>\r\n

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  1. Identify the aldehyde, ketone, acid, ester, and ether functional groups.<\/li>\r\n \t
  2. Use proper naming conventions for aldehyde, ketone, carboxylic acid, and ester- and ether-containing molecules.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\nThere are other functional groups that contain oxygen atoms. A carbonyl group<\/strong> is formed when an O atom and a C atom are joined by a double bond. In this\u00a0diagram, the R group represents any hydrocarbon chain:\r\n

    [latex]\\chemfig{R-[:30](=[:90]O)-[:-30]\\text{R or H}}[\/latex]<\/p>\r\nIf one bond of the carbonyl group is made to a\u00a0hydrogen\u00a0atom, then the molecule is further classified as an aldehyde<\/strong>. When naming aldehydes, the main chain of C atoms must include the carbon in the carbonyl group, which is numbered as position 1 in the carbon chain. The parent name of the hydrocarbon is used, but the suffix -al<\/em> is appended. (Do not confuse -al<\/em> with -ol<\/em>, which is the suffix used for alcohols.) So we have:\r\n

    [latex]\\begin{array}{ccc}\r\n\\chemname[1.5em]{\\chemfig{O=[:-90](-[:-150]H)-[:-30]H}}{methanal}&\\hspace{5em}\\chemname[1.5em]{\\chemfig{O=[:-90](-[:-150])-[:-30]H}}{ethanal}&\\hspace{5em}\\chemname[1.5em]{\\chemfig{O=[:-90](-[:-150]-[:150])-[:-30]H}}{propanal}\r\n\\end{array}[\/latex]<\/p>\r\nMethanal has a common name with which you may be familiar: formaldehyde. The main thing to note about aldehydes is that the carbonyl group is at the end<\/em> of a carbon chain.\r\n\r\nA carbonyl group in the middle of a carbon chain implies that both remaining bonds of the carbonyl group are made to C atoms. This type of molecule is called a ketone<\/strong>. Despite the fact that aldehydes and ketones have the same carbonyl group, they have different chemical and physical properties and are properly grouped as two different types of compounds. The smallest ketone has three C atoms in it. When naming a ketone, we take the name of the parent hydrocarbon and change the suffix to -one<\/em>:\r\n

    [latex]\\chemname[1.5em]{\\chemfig{O=[:-90](-[:-30])-[:-150]}}{propanone}[\/latex]<\/p>\r\nThe common name for propanone is acetone. With larger ketones, we must use a locant number to indicate the position of the carbonyl group just before the suffix, as we did with alkenes and alkynes:\r\n

    [latex]\\chemname[1.5em]{\\chemfig{O=[:-90](-[:-30]-[:30])-[:-150]-[:150]}}{3-pentanone}[\/latex]<\/p>\r\nThere is a non-IUPAC\u00a0way to name ketones that is commonly used as well: name the alkyl groups that are attached to the carbonyl group and add the word ketone<\/em> to the name. So propanone can also be called dimethyl ketone, while butan-2-one is called methyl ethyl ketone.\r\n

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    Example 16.9<\/p>\r\n\r\n<\/header>\r\n

    \r\n\r\nDraw the structure of 2-pentanone.\r\n\r\nSolution<\/em>\r\nThis molecule has five C atoms in a chain, with the carbonyl group on the second C atom. Its structure is:\r\n

    [latex]\\chemfig{-[:30](=[:90]O)-[:-30]-[:30]-[:-30]}[\/latex]<\/p>\r\nTest Yourself<\/em>\r\nDraw the structure of methyl butyl ketone.\r\nAnswer<\/em>\r\n[latex]\\chemfig{-[:30](=[:90]O)-[:-30]-[:30]-[:-30]-[:30]}[\/latex]\r\n\r\n<\/div>\r\n<\/div>\r\nThe combination of a carbonyl functional group and a\u00a0hydroxyl\u00a0group makes the carboxyl group<\/strong>.\r\n

    [latex]\\chemfig{O=[:-90](-[:-150]R)-[:-30]\\ce{OH}}[\/latex]<\/p>\r\nMolecules with a carboxyl group are called carboxylic acids<\/strong>. As with aldehydes, the functional group in carboxylic acids is at the end of a carbon chain. Also as with aldehydes, the C atom in the functional group is counted as one of the C atoms that defines the parent hydrocarbon name. To name carboxylic acids, the parent name of the hydrocarbon is used, but the suffix -oic acid<\/em> is added:\r\n

    [latex]\\chemname[1.5em]{\\chemfig{O=[:-90](-[:-150]H)-[:-30]\\ce{OH}}}{methanoic acid}\\hspace{5em}\\chemname[1.5em]{\\chemfig{O=[:-90](-[:-150])-[:-30]\\ce{OH}}}{ethanoic acid}\\hspace{5em}\\chemname[1.5em]{\\chemfig{O=[:-90](-[:-150]-[:150])-[:-30]\\ce{OH}}}{propanoic acid}[\/latex]<\/p>\r\nMethanoic acid and ethanoic acid are also called formic acid and acetic acid, respectively. Formic acid is the compound that makes certain ant bites sting, while acetic acid is the active substance in vinegar.\r\n\r\nHow acidic are carboxylic acids? It turns out that they are not very acidic. No carboxylic acid is on the list of strong acids (Table 12.1 \"Strong Acids and Bases\"<\/a>). (For more information about strong acids, see the section \"Strong and Weak Acids and Bases and Their Salts.\"<\/a>) This means that all carboxylic acids are weak acids. A 1 M solution of formic acid is only about 1.3% dissociated into H+<\/sup> ions and formate ions, while a similar solution of acetic acid is ionized by about only 0.4%. Some carboxylic acids are stronger \u2014 for example, trichloroacetic acid is about 45% dissociated in aqueous solution. But no carboxylic acid approaches the 100% dissociation amount required by the definition of a strong acid.\r\n\r\nAs their name suggests, however, carboxylic acids do act like acids in the presence of bases. The H atom in the carboxyl group comes off as the H+<\/sup> ion, leaving a carboxylate<\/strong> ion:\r\n

    [latex]\\begin{array}{ccccccc}\r\n\\chemfig{(=[:90]O)(-[:-150]R)-[:-30]\\ce{OH}}&+&\\ce{OH}^{\\ominus}&\\longrightarrow&\\chemname[1.5em]{\\chemfig{(=[:90]O)(-[:-150]R)-[:-30]O^{\\ominus}}}{carboxylate ion}&+&\\ce{H2O} \\\\\r\n\\end{array}[\/latex]<\/p>\r\nCarboxylate ions are named from the acid name: the -oic acid<\/em> is replaced with -oate<\/em> to name the ion.\r\n

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    Example 16.10<\/p>\r\n\r\n<\/header>\r\n

    \r\n\r\nComplete the chemical reaction. Can you name the carboxylate ion formed?\r\n

    [latex]\\begin{array}{ccccc}\r\n\\chemfig{(=[:90]O)(-[:-150])-[:-30]\\ce{OH}}&+&\\ce{OH}^{\\ominus}&\\longrightarrow&?\r\n\\end{array}[\/latex]<\/p>\r\nSolution<\/em>\r\nThe OH\u2013<\/sup> ion removes the H atom that is part of the carboxyl group:\r\n

    [latex]\\begin{array}{ccccccc}\r\n\\chemfig{(=[:90]O)(-[:-150])-[:-30]\\ce{OH}}&+&\\ce{OH}^{\\ominus}&\\longrightarrow&\\chemfig{(=[:90]O)(-[:-150])-[:-30]O^{\\ominus}}&+&\\ce{H2O}\r\n\\end{array}[\/latex]<\/p>\r\nThe carboxylate ion, which has the condensed structural formula CH3<\/sub>CO2<\/sub>\u2212<\/sup>, is the ethanoate ion, but it is commonly called the acetate ion.\r\n\r\nTest Yourself<\/em>\r\nComplete the chemical reaction. Can you name the carboxylate ion formed?\r\n

    [latex]\\begin{array}{ccccc}\r\n\\chemfig{(=[:90]O)(-[:-150]H)-[:-30]\\ce{OH}}&+&\\ce{OH}^{\\ominus}&\\longrightarrow&?\r\n\\end{array}[\/latex]<\/p>\r\nAnswer<\/em>\r\n

    [latex]\\begin{array}{ccccccc}\r\n\\chemfig{(=[:90]O)(-[:-150]H)-[:-30]\\ce{OH}}&+&\\ce{OH}^{\\ominus}&\\longrightarrow&\\chemfig{(=[:90]O)(-[:-150]H)-[:-30]O^{\\ominus}}&+&\\ce{H2O}\r\n\\end{array}[\/latex]<\/p>\r\nThe ion is the methanoate ion, which is commonly called the formate ion.\r\n\r\n<\/div>\r\n<\/div>\r\nOne reaction to consider is that of a carboxylic acid and an alcohol. When combined under the proper conditions, a water molecule will be removed, and the remaining pieces will combine to form a new functional group \u2014 the ester<\/strong>\u00a0group:\r\n

    [latex]\\begin{array}{ccccccc}\r\n\\chemfig{(=[:90]O)(-[:-30]\\ce{OH})-[:-150]R}&+&\\chemfig{R'-\\ce{OH}}&\\longrightarrow&\\chemname[1.5em]{\\chemfig{(=[:90]O)(-[:-30]OR')-[:-150]R}}{ester}&+&\\ce{H2O}\r\n\\end{array}[\/latex]<\/p>\r\nNote how the acid molecule contributes one alkyl side (represented by R), while the alcohol contributes the other side (represented by R\u2032). Esters are named using the alkyl group name from the alcohol plus the carboxylate name from the acid\u2014for example, this molecule is called methyl propanoate:\r\n

    [latex]\\chemname[1.5em]{\\chemfig{-[:-30]-[:30](=[:90]O)-[:-30]O-[:30]}}{methyl propanoate}[\/latex]<\/p>\r\n\r\n

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    Chemistry Is Everywhere: Esters, Fragrances, and Flavourings<\/h1>\r\nEsters are very interesting compounds, in part because many have pleasant odours and flavours. (Remember, never taste anything in the chemistry lab!) Many esters occur naturally and contribute to the fragrance\u00a0of flowers and the taste of fruits. Other esters are synthesized industrially and are added to food products to improve their smell or taste. It is likely that if you eat a product whose ingredients include artificial flavourings, those flavourings are esters. Here are some esters and their uses, thanks to their odours, flavours, or both:\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
    Ester<\/th>\r\nTastes\/Smells Like<\/th>\r\n<\/tr>\r\n
    allyl hexanoate<\/td>\r\npineapple<\/td>\r\n<\/tr>\r\n
    benzyl acetate<\/td>\r\npear<\/td>\r\n<\/tr>\r\n
    butyl butanoate<\/td>\r\npineapple<\/td>\r\n<\/tr>\r\n
    ethyl butanoate<\/td>\r\nbanana<\/td>\r\n<\/tr>\r\n
    ethyl hexanoate<\/td>\r\npineapple<\/td>\r\n<\/tr>\r\n
    ethyl heptanoate<\/td>\r\napricot<\/td>\r\n<\/tr>\r\n
    ethyl pentanoate<\/td>\r\napple<\/td>\r\n<\/tr>\r\n
    isobutyl formate<\/td>\r\nraspberry<\/td>\r\n<\/tr>\r\n
    isobutyl acetate<\/td>\r\npear<\/td>\r\n<\/tr>\r\n
    methyl phenylacetate<\/td>\r\nhoney<\/td>\r\n<\/tr>\r\n
    nonyl caprylate<\/td>\r\norange<\/td>\r\n<\/tr>\r\n
    pentyl acetate<\/td>\r\napple<\/td>\r\n<\/tr>\r\n
    propyl ethanoate<\/td>\r\npear<\/td>\r\n<\/tr>\r\n
    propyl isobutyrate<\/td>\r\nrum<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\nFinally, the ether<\/strong>\u00a0functional group is an O atom that is bonded to two organic groups:\r\n

    [latex]\\chemfig{R-O-R'}[\/latex]<\/p>\r\nThe two R groups may be the same or different. Naming ethers is like the alternate way of naming ketones. In this case, the R groups are named sequentially, and the word ether<\/em> is appended. The molecule\u00a0CH3<\/sub>OCH3<\/sub> is dimethyl ether, while\u00a0CH3<\/sub>OCH2<\/sub>CH3<\/sub> is methyl ethyl ether. Diethyl ether, another ether, was once used as an anaesthetic, but its flammability and toxicity caused it to fall out of favor. Smaller ether molecules that are liquids at room temperature are common solvents for organic chemical reactions.\r\n\r\n<\/div>\r\n

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    Key Takeaways<\/p>\r\n\r\n<\/header>\r\n

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