{"id":2536,"date":"2018-06-19T20:34:54","date_gmt":"2018-06-19T20:34:54","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/1-8-2-bronsted-lowry-acids-and-bases\/"},"modified":"2018-08-06T12:44:45","modified_gmt":"2018-08-06T12:44:45","slug":"6-3-bronsted-lowry-acids-bases","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-potsdam-organicchemistry\/chapter\/6-3-bronsted-lowry-acids-bases\/","title":{"raw":"6.3. Bronsted-Lowry acids\/bases","rendered":"6.3. Bronsted-Lowry acids\/bases"},"content":{"raw":"
\r\n
\r\n
\r\n

A: The Br\u00f8nsted-Lowry definition of acidity and basicity<\/h1>\r\nWe\u2019ll begin our discussion of acid-base chemistry with a couple of essential definitions. The first of these was proposed in 1923 by the Danish chemist Johannes Br\u00f8nsted and the English chemist Thomas Lowry, and has come to be known as the Br\u00f8nsted-Lowry definition of acidity and basicity<\/strong>.\u00a0 An acid, by the Br\u00f8nsted-Lowry definition, is a species which acts as a proton donor (i.e., it gives away an H+<\/sup>), while a base is a proton (H+<\/sup>) acceptor.\u00a0 One of the most familiar examples of a Br\u00f8nsted-Lowry acid-base reaction is between hydrochloric acid and hydroxide ion:\r\n\r\n\"\"\r\n\r\nIn this reaction, a proton is transferred from HCl (the acid, or proton donor<\/em>) to hydroxide ion (the base, or proton acceptor<\/em>). As we learned in the previous chapter, curved arrows depict the movement of electrons in this bond-breaking and bond-forming process.\r\n\r\nAfter a Br\u00f8nsted-Lowry acid donates a proton, what remains is called the conjugate base<\/strong>.\u00a0 Chloride ion is thus the conjugate base of hydrochloric acid. Conversely, when a Br\u00f8nsted-Lowry base accepts a proton it is converted into its conjugate acid<\/strong> form: water is thus the conjugate acid of hydroxide ion.\r\n\r\nHere is an organic acid-base reaction between acetic acid and methylamine:\r\n\r\n\"image002.png\"\r\n\r\nIn the reverse of this reaction, acetate ion is the base and methylammonium ion (protonated methylamine) is the acid.\r\n\r\n\"\"\r\n\r\nWhat makes a compound acidic (likely to donate a proton) or basic (likely to accept a proton)? Answering that question is one of our main jobs in this chapter, and will require us to put to use much of what we learned about organic structure in the first two chapters, as well as the ideas about thermodynamics that we reviewed in chapter 5.\r\n\r\nFor now, let's just consider one common property of bases: in order to act as a base, a molecule must have a reactive pair of electrons<\/em>.\u00a0 In all of the acid-base reactions we'll see in this chapter, the basic species has an atom with a lone pair of electrons. When methylamine acts as a base, for example, the lone pair of electrons on the nitrogen atom is used to form a new bond to a proton.\u00a0 A negative charge often (but not always!) indicates that a structure (in this case, an anion) is likely to act as a base.\r\n\r\nClearly, methylammonium ion cannot act as a base \u2013 it does not have a reactive pair of electrons with which to accept a proton.\r\n\r\n\"\"\r\n\r\nLater, in chapter 10, we will study reactions in which a pair of electrons in a pi bond of an alkene acts in a basic fashion - but for now, will concentrate on the basicity of non-bonding (lone pair) electrons.\r\n
\r\n
\r\n

Exercise<\/h3>\r\nComplete the reactions below - in other words, draw structures for the missing conjugate acids and conjugate bases that result from the curved arrows provided.\r\n\r\n\"\"\r\n\r\n[reveal-answer q=\"191829\"]Show Solution[\/reveal-answer]\r\n[hidden-answer a=\"191829\"]\"\"\r\n\r\n[\/hidden-answer]\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n
\u00a0In summary,<\/div>\r\n
\r\n