{"id":127281,"date":"2024-11-18T13:53:57","date_gmt":"2024-11-18T06:53:57","guid":{"rendered":"https:\/\/hotvideos24.online\/?p=127281"},"modified":"2024-11-18T13:53:57","modified_gmt":"2024-11-18T06:53:57","slug":"this-strange-crystal-has-two-melting-points-and-we-finally-know-why-sciencealert","status":"publish","type":"post","link":"https:\/\/hotvideos24.online\/?p=127281","title":{"rendered":"This Strange Crystal Has Two Melting Points And We Finally Know Why : ScienceAlert"},"content":{"rendered":"<p> <script async src=\"https:\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js?client=ca-pub-3711241968723425\"\r\n     crossorigin=\"anonymous\"><\/script>\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:block\"\r\n     data-ad-format=\"fluid\"\r\n     data-ad-layout-key=\"-fb+5w+4e-db+86\"\r\n     data-ad-client=\"ca-pub-3711241968723425\"\r\n     data-ad-slot=\"7910942971\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><br \/>\n<\/p>\n<div>\n<p>In 1896, German chemist Emil Fischer noted something very strange about a molecule named acetaldehyde phenylhydrazone. Identical batches of the crystalline compound appeared to have wildly different melting points.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>Some batches, he found, melted at temperatures of around 65 degrees Celsius (149 Fahrenheit). Others at 100 degrees Celsius.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>It was, in a word, utterly bizarre. No other substance was known to behave this way. Nor should it. According to the laws of  <a href=\"https:\/\/www.sciencealert.com\/thermodynamics\" class=\"lar_link lar_link_outgoing\" data-linkid=\"73052\" data-postid=\"142871\" rel=\"nofollow noopener\" target=\"_self\">thermodynamics<\/a> that describe the way the physical world behaves, such a result should be impossible.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>Scientists were stumped. They rushed <a href=\"https:\/\/chemistry-europe.onlinelibrary.wiley.com\/doi\/10.1002\/cber.19030360115\">to see<\/a> if Fischer <a href=\"https:\/\/chemistry-europe.onlinelibrary.wiley.com\/doi\/10.1002\/jlac.19053420103\">had made<\/a> a <a href=\"https:\/\/pubs.rsc.org\/en\/content\/articlelanding\/1911\/ct\/ct9119902085\">mistake<\/a>. Imagine their consternation when they were able to replicate his observations.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>More than 120 years after Fischer&#8217;s original discovery, in 2019, an international team of researchers led by chemist Terry Threfall of the University of Southampton in the UK finally found and published the answer. Fischer (who went on to <a href=\"https:\/\/www.sciencehistory.org\/education\/scientific-biographies\/emil-fischer\/\">win a 1902 Nobel prize for other work<\/a>, so he was clearly no quack) had observed something real; but not, as it would turn out, anything that would break thermodynamics.<\/p>\n<figure id=\"attachment_142877\" aria-describedby=\"caption-attachment-142877\" style=\"width: 642px\" class=\"wp-caption alignnone\"><img decoding=\"async\" src=\"https:\/\/www.sciencealert.com\/images\/2024\/11\/aph.jpg\" alt=\"This Strange Compound Appeared to Flout Thermodynamics. Now, We Know How\" width=\"642\" height=\"564\" class=\"size-full wp-image-142877\" srcset=\"https:\/\/www.sciencealert.com\/images\/2024\/11\/aph.jpg 642w, https:\/\/www.sciencealert.com\/images\/2024\/11\/aph-472x415.jpg 472w, https:\/\/www.sciencealert.com\/images\/2024\/11\/aph-600x527.jpg 600w\" sizes=\"auto, (max-width: 642px) 100vw, 642px\" loading=\"lazy\"\/><figcaption id=\"caption-attachment-142877\" class=\"wp-caption-text\">The structure of acetaldehyde phenylhydrazone. (Bernades et al., <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/acs.cgd.8b01459\"><em>Cryst. Growth Des.<\/em><\/a>, 2019)<\/figcaption><\/figure>\n<p>The culprit? An absolutely miniscule contamination, so small that it is all but undetectable. When acetaldehyde phenylhydrazone melts, it becomes one of two liquids, based on whether the compound has been exposed to a base or an acid. The former appears at the higher melting point; and the latter at the lower.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>&#8220;It is just exceedingly satisfying to be able to understand such an ancient puzzle, especially one which baffled such an eminent scientist who became a Nobel Prize winner,&#8221; <a href=\"https:\/\/www.southampton.ac.uk\/chemistry\/news\/2019\/08\/07-southampton-chemist-solves-nobel-laureates-120-year-old-crystal-mystery.page\">Threlfall said<\/a>.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>&#8220;The observation of such behavior will be exceedingly rare because it depends on the molecules in the crystal and in the liquid having different geometries, which is unusual. Furthermore, it depends also on the conversion by acid being both possible and rapid.&#8221;<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>The compound is made by dissolving solid <a href=\"https:\/\/en.wikipedia.org\/wiki\/Acetaldehyde\">acetaldehyde<\/a> and adding both liquid <a href=\"https:\/\/en.wikipedia.org\/wiki\/Phenylhydrazine\">phenylhydrazine<\/a> and aqueous ethanol, and chilling until the mixture freezes and forms solid crystals. To then discover the melting point of the newly formed acetaldehyde phenylhydrazone, you have to re-melt it.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>This is where the problems emerged. To understand why acetaldehyde phenylhydrazone melts at two distinct temperatures, the researchers first investigated its solid form. But the most cutting edge probes failed to turn up an answer.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>All analyses, performed by Threlfall&#8217;s team and other recent efforts, failed to find a single difference between acetaldehyde phenylhydrazone samples that melted at the lower temperature, and samples that melted at the higher. These techniques included X-ray diffraction, nuclear magnetic resonance, and IR spectroscopy. As far as scientists could tell, the crystals were identical.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>The next step was to investigate the liquid the crystals became after melting.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>And there, the researchers got a result. There was a subtle, and temporary, but distinct difference. Although the compounds had the same molecular formula, the structure of the initial melt was slightly different, depending on the temperature.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>The compound contains a methyl group that is able to have two distinct configurations, known as the Z isomer and the E isomer.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>In its solid phase, the material almost exclusively consists of the Z isomer.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>The most stable liquid phase is a mix of about one-third Z isomer to two-thirds E isomer. The lower of the two melting points immediately produces the Z and E mix, while the higher melting point is entirely Z, before switching to part E.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>A clue was given in <a href=\"https:\/\/chemistry-europe.onlinelibrary.wiley.com\/doi\/10.1002\/jlac.19053420103\">a 1905 paper<\/a>, which pointed out that acetaldehyde phenylhydrazone was extremely sensitive to acid. Threlfall and his team tried exposing their samples to vapors of acid and ammonia. And they found that exposure to just a tiny bit of one or the other could reliably influence the compound&#8217;s melting point. The acid acts as a catalyst to speed the shift from the Z to E isomer, lowering the melting point in the process.<\/p>\n<figure id=\"attachment_142880\" aria-describedby=\"caption-attachment-142880\" style=\"width: 642px\" class=\"wp-caption alignnone\"><img decoding=\"async\" src=\"https:\/\/www.sciencealert.com\/images\/2024\/11\/aph-overlap.jpg\" alt=\"This Strange Compound Appeared to Flout Thermodynamics. Now, We Know How\" width=\"642\" height=\"310\" class=\"size-full wp-image-142880\" srcset=\"https:\/\/www.sciencealert.com\/images\/2024\/11\/aph-overlap.jpg 642w, https:\/\/www.sciencealert.com\/images\/2024\/11\/aph-overlap-600x290.jpg 600w\" sizes=\"auto, (max-width: 642px) 100vw, 642px\" loading=\"lazy\"\/><figcaption id=\"caption-attachment-142880\" class=\"wp-caption-text\">Molecular structure overlap of high-melting (blue) and low-melting (red) forms of acetaldehyde phenylhydrazone. (Bernades et al., <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/acs.cgd.8b01459\"><em>Cryst. Growth Des.<\/em><\/a>, 2019)<\/figcaption><\/figure>\n<p>&#8220;If an element or compound can exist in two or more distinct crystalline forms, then each form will have different Gibbs energies and melt at its own distinct temperature,&#8221; <a href=\"https:\/\/www.southampton.ac.uk\/chemistry\/news\/2019\/08\/07-southampton-chemist-solves-nobel-laureates-120-year-old-crystal-mystery.page\">said chemist Simon Coles<\/a> of the University of Southampton.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>&#8220;In this case, the molecules of the crystal are in the cis geometry \u2013 of groups pointing towards each other \u2013 and melt to an identical geometry in the absence of acid at 100 degrees Celsius. However, in the presence of even a trace of acid, the molecules convert on melting to the trans geometry of groups pointing away from each other. This liquid has a smaller Gibbs energy and is more stable, so the melting point becomes 65 degrees Celsius.&#8221;<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>It&#8217;s similar to the effect salt has on water: adding salt to a pot of water raises the freezing and boiling points. Where it takes a lot of salt to invoke a significant change to water&#8217;s phase transitions, it takes so little acid to alter acetaldehyde phenylhydrazone that it took more than a century \u2013 and Threlfall and his colleagues a decade \u2013 to figure it out.<\/p>\n<p><!-- START single\/mrec --><br \/>\n<!-- END single\/mrec --><\/p>\n<p>This research is a real testament to human curiosity and tenacity. And it gives us hope for the future. How many more mysteries will be solved in the years stretching into a glittering future of discovery?<\/p>\n<p>The research was published in 2019 in <a href=\"https:\/\/pubs.acs.org\/doi\/10.1021\/acs.cgd.8b01459\"><i>Crystal Growth &amp; Design<\/i><\/a>.<\/p>\n<\/p><\/div>\n<p><script async src=\"https:\/\/pagead2.googlesyndication.com\/pagead\/js\/adsbygoogle.js?client=ca-pub-3711241968723425\"\r\n     crossorigin=\"anonymous\"><\/script>\r\n<ins class=\"adsbygoogle\"\r\n     style=\"display:block\"\r\n     data-ad-format=\"fluid\"\r\n     data-ad-layout-key=\"-fb+5w+4e-db+86\"\r\n     data-ad-client=\"ca-pub-3711241968723425\"\r\n     data-ad-slot=\"7910942971\"><\/ins>\r\n<script>\r\n     (adsbygoogle = window.adsbygoogle || []).push({});\r\n<\/script><br \/>\n<br \/><div data-type=\"_mgwidget\" data-widget-id=\"1660802\">\r\n<\/div>\r\n<script>(function(w,q){w[q]=w[q]||[];w[q].push([\"_mgc.load\"])})(window,\"_mgq\");\r\n<\/script>\r\n<br \/>\n<br \/><a href=\"https:\/\/www.sciencealert.com\/this-strange-crystal-has-two-melting-points-and-we-finally-know-why\">Source link <\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>In 1896, German chemist Emil Fischer noted something very strange about a molecule named acetaldehyde phenylhydrazone. Identical batches of the crystalline compound appeared to have wildly different melting points. Some &hellip; <a href=\"https:\/\/hotvideos24.online\/?p=127281\" class=\"more-link\">Read More<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8628],"tags":[],"class_list":["post-127281","post","type-post","status-publish","format-standard","hentry","category-science","entry"],"_links":{"self":[{"href":"https:\/\/hotvideos24.online\/index.php?rest_route=\/wp\/v2\/posts\/127281","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/hotvideos24.online\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/hotvideos24.online\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/hotvideos24.online\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/hotvideos24.online\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=127281"}],"version-history":[{"count":0,"href":"https:\/\/hotvideos24.online\/index.php?rest_route=\/wp\/v2\/posts\/127281\/revisions"}],"wp:attachment":[{"href":"https:\/\/hotvideos24.online\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=127281"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/hotvideos24.online\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=127281"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/hotvideos24.online\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=127281"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}