{"id":1051,"date":"2019-10-31T11:27:32","date_gmt":"2019-10-31T11:27:32","guid":{"rendered":"http:\/\/chemdictionary.org\/?p=1051"},"modified":"2019-10-31T11:27:42","modified_gmt":"2019-10-31T11:27:42","slug":"curly-arrows-mechnisms","status":"publish","type":"post","link":"https:\/\/chemdictionary.org\/curly-arrows-mechnisms\/","title":{"rendered":"Curly Arrows Mechanisms"},"content":{"rendered":"\n<h2><strong>Introduction<\/strong><\/h2>\n\n\n\n<p>There are different types of\narrows we meet in organic chemistry. Before explaining curly arrows, let\u2019s have\na glance at these types individually.<\/p>\n\n\n\n<ul><li><strong>The forward arrow (\u2192)<\/strong>,\nwhich is also known as reaction arrow. The goal of this arrow is to indicate an\naction. There is no hard and fast rule about what is supposed to write above or\nbelow an arrow but reagents are mostly written above and solvents tend to go\nbelow. <\/li><li><strong>The Equilibrium arrow (<\/strong><strong>\u21cc<\/strong><strong>),<\/strong> indicates a reversible reaction.<\/li><li><strong>The resonance arrow (\u2194), <\/strong>this\ndouble-headed arrow indicates the resonance structures of two or more species.\nThere is a difference in the arrangement of their electrons and nothing else.\nIt is important to observe that the molecule does not shuffle back and forth\nbetween these forms but rather they give a true picture that the molecule is a\ncombination or hybrid of these structures.<\/li><\/ul>\n\n\n\n<ul><li> The broken arrow is used to indicate reactions that don\u2019t work i.e. in nucleophilic substitutions fluorine is considered as a bad leaving group and quinine cannot be synthesized from the oxidation of aniline.<\/li><\/ul>\n\n\n\n<ul><li><strong>The Retrosynthesis arrow<\/strong> is meant to illustrate the process of breaking down a complex molecule into simpler starting materials. This is considered as a useful planning device to highlight a key strategy used for a molecule built up.<\/li><li><strong>Curly arrows<\/strong> are used to show the movement of both the electron pairs and single electrons during organic reaction mechanisms. One can\u2019t use curly arrows for any other purpose.<\/li><\/ul>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img loading=\"lazy\" width=\"538\" height=\"620\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-83.png\" alt=\"\" class=\"wp-image-1052\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-83.png 538w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-83-260x300.png 260w\" sizes=\"(max-width: 538px) 100vw, 538px\" title=\"\"><\/figure><\/div>\n\n\n\n<p><strong>Curly\narrows showing the movement of electron pair<\/strong><\/p>\n\n\n\n<ul><li><strong>Symbolic representation<\/strong><\/li><\/ul>\n\n\n\n<figure class=\"wp-block-image\"><img loading=\"lazy\" width=\"475\" height=\"179\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-84.png\" alt=\"\" class=\"wp-image-1053\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-84.png 475w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-84-300x113.png 300w\" sizes=\"(max-width: 475px) 100vw, 475px\" title=\"\"><\/figure>\n\n\n\n<ul><li><strong>Explanation<\/strong><\/li><\/ul>\n\n\n\n<p>The tail of an arrow indicates\nwhere the electron pair starts. One must show the electron pair either as a\nbond or if it is alone pair than you have to represent it as a pair of dots.\nDon\u2019t forget that a lone pair indicate a pair of electrons at the bonding level\nwhich is not currently being used to join on to anything else.<\/p>\n\n\n\n<p>The head of an arrow is where\nyou want the electron pair to end up.<\/p>\n\n\n\n<ul><li><strong>Example <\/strong><\/li><\/ul>\n\n\n\n<p>Let\u2019s take an example of ethene and hydrogen bromide. Here one of the two bonds between the two carbon atoms breaks. Simply, that bond is a pair of electrons. These electrons move towards hydrogen of the HBr to form a new bond. At once the pair of electrons in the hydrogen-bromine bond moves down on to the bromine atom.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img loading=\"lazy\" width=\"194\" height=\"180\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-85.png\" alt=\"\" class=\"wp-image-1054\" title=\"\"><\/figure><\/div>\n\n\n\n<p>It is not necessary to draw the pairs of electrons in the bonds as two dots. It\u2019s enough to draw a line to represent bond but you can put two dots too if you are willing.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img loading=\"lazy\" width=\"208\" height=\"235\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-86.png\" alt=\"\" class=\"wp-image-1055\" title=\"\"><\/figure><\/div>\n\n\n\n<p>Note\nthat the arrowhead points between the Carbon and hydrogen because that&#8217;s where\nthe electron pair ends up. Also, notice that the curly arrow is used to\nrepresent the electron movement between H and Br even though the electron pair\nmoves straight down. We have to indicate electron pair movement as curly arrows\nand not as a straight one.<\/p>\n\n\n\n<p>The\nsecond step of this reaction explains how we can use a curly arrow if a lone\npair of an electron is involved.<\/p>\n\n\n\n<p>The first step leaves us with a positive charge on the right-hand carbon atom and a negative bromide ion. we can think of the electron shown on the bromide ion as being the one which originally made up the hydrogen-bromine bond.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img loading=\"lazy\" width=\"194\" height=\"146\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-87.png\" alt=\"\" class=\"wp-image-1056\" title=\"\"><\/figure><\/div>\n\n\n\n<p>Bromide\nion having a lone pair on it moves to form a new bond between bromine and the\nright-hand carbon atom. This movement is again shown by a curly arrow. Observe\nagain, that the curly arrow points between the carbon and the bromine because\nof it a point where the electron pair end up.<\/p>\n\n\n\n<p>This gives us a product of this reaction named bromoethane<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img loading=\"lazy\" width=\"216\" height=\"144\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-88.png\" alt=\"\" class=\"wp-image-1057\" title=\"\"><\/figure><\/div>\n\n\n\n<p><strong>Curly\narrows showing the movement of a single electron<\/strong><\/p>\n\n\n\n<ul><li><strong>Symbolic representation<\/strong><\/li><\/ul>\n\n\n\n<p style=\"text-align:center\">the common use of the curly arrows is to indicate the movement of pairs of electrons but we can use the same arrows to indicate the movement of a single electron. But to indicate a single electron movement we have put a single line at the arrowhead rather than two lines.<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img loading=\"lazy\" width=\"454\" height=\"125\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-89.png\" alt=\"\" class=\"wp-image-1058\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-89.png 454w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-89-300x83.png 300w\" sizes=\"(max-width: 454px) 100vw, 454px\" title=\"\"><\/figure>\n\n\n\n<ul><li><strong>Example:<\/strong><\/li><\/ul>\n\n\n\n<p>Let\u2019s take an example of the polymerization of ethene, the first step can be shown as follows<\/p>\n\n\n\n<figure class=\"wp-block-image\"><img loading=\"lazy\" width=\"520\" height=\"74\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-90.png\" alt=\"\" class=\"wp-image-1059\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-90.png 520w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-90-300x43.png 300w\" sizes=\"(max-width: 520px) 100vw, 520px\" title=\"\"><\/figure>\n\n\n\n<p>We can draw the dots showing\nthe concerning electrons. The half arrows indicate where electrons will go.<\/p>\n\n\n\n<p><strong>Curly\nArrows Mechanism (Golden Rules)<\/strong><\/p>\n\n\n\n<ol><li>Curly\narrows are used to indicate the movement of pairs of electrons<\/li><li>Curly\narrows always flow from an electron-rich species to an electron-poor species.\ni.e. from the nucleophile to electrophile.<\/li><li>They\nget a start from lone pairs or bonds and end up either between a pair of atoms\non an atom.<\/li><li>There\nshould be a balance in charges in any particular step.<\/li><li>If you\ntake out an electron from a bond, that bond will be broken.<\/li><li>If you\nplace electrons between two atoms, a bond is formed.<\/li><\/ol>\n\n\n\n<p>Consider a simple example<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><img loading=\"lazy\" width=\"454\" height=\"227\" src=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-91.png\" alt=\"\" class=\"wp-image-1060\" srcset=\"https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-91.png 454w, https:\/\/chemdictionary.org\/wp-content\/uploads\/2019\/10\/image-91-300x150.png 300w\" sizes=\"(max-width: 454px) 100vw, 454px\" title=\"\"><\/figure><\/div>\n\n\n\n<p>The curly arrow in an above\nreaction starts from a lone pair of the oxygen (a nucleophile) and ends on the\nproton (an electrophile). This shows that it flows from an electron-rich\nspecies to an electron-poor species. Charges are in balance as there is a\npositive charge on both sides of the equilibrium arrows. As the electrons are\nplaced between two atoms (the oxygen and the proton) a bond is created.<\/p>\n\n\n\n<h3>References<\/h3>\n\n\n\n<p>http:\/\/www.chem.ucalgary.ca\/courses\/350\/Carey5th\/Ch01\/ch1-6-1.html<\/p>\n\n\n\n<p>http:\/\/www.ch.ic.ac.uk\/local\/organic\/tutorial\/arrow_pushing.pdf<\/p>\n\n\n\n<p>https:\/\/www.dur.ac.uk\/chemistry\/outreach\/dusting\/students\/arrows\/<\/p>\n\n\n\n<p>https:\/\/www.chemguide.co.uk\/basicorg\/conventions\/curlies.html?fbclid=IwAR2cyDNTZ-pXZnNU8uBAwl6GBLC37FYVskCj9RqfkyrskX8qMMNQOtbtxko<\/p>\n\n\n\n<p>https:\/\/www.masterorganicchemistry.com\/2011\/02\/09\/the-8-types-of-arrows-in-organic-chemistry-explained\/<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Introduction There are different types of arrows we meet in organic chemistry. Before explaining curly arrows, let\u2019s have a glance at these types individually. The forward arrow (\u2192), which is also known as reaction arrow. The goal of this arrow is to indicate an action. There is no hard and fast rule about what is &#8230; <a title=\"Curly Arrows Mechanisms\" class=\"read-more\" href=\"https:\/\/chemdictionary.org\/curly-arrows-mechnisms\/\" aria-label=\"More on Curly Arrows Mechanisms\">Read more<\/a><\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"rating_form_position":"","rating_results_position":"","mr_structured_data_type":""},"categories":[62],"tags":[],"multi-rating":{"mr_rating_results":[{"adjusted_star_result":0,"star_result":0,"total_max_option_value":5,"adjusted_score_result":0,"score_result":0,"percentage_result":0,"adjusted_percentage_result":0,"count":0,"post_id":1051}]},"_links":{"self":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1051"}],"collection":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/comments?post=1051"}],"version-history":[{"count":2,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1051\/revisions"}],"predecessor-version":[{"id":1097,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/posts\/1051\/revisions\/1097"}],"wp:attachment":[{"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/media?parent=1051"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/categories?post=1051"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/chemdictionary.org\/wp-json\/wp\/v2\/tags?post=1051"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}