{"id":29665,"date":"2025-09-03T11:25:18","date_gmt":"2025-09-03T10:25:18","guid":{"rendered":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29665"},"modified":"2025-09-03T11:29:43","modified_gmt":"2025-09-03T10:29:43","slug":"alternative-reactions-of-the-n%e2%89%a1n-triple-bond-in-a-nitric-oxide-dimer-forming-the-trimer-n3o3","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29665","title":{"rendered":"Alternative reactions of the N\u2261N &#8220;triple bond&#8221; in a nitric oxide dimer: forming the trimer N<sub>3<\/sub>O<sub>3<\/sub>."},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"29665\">\n<p>In the previous post<span id=\"cite_ITEM-29665-0\" name=\"citation\"><a href=\"#ITEM-29665-0\">[1]<\/a><\/span> I mooted the possibility that a high energy form of the dimer of nitric oxide <strong>1<\/strong> might nonetheless be able to be detected using suitable traps (such as hydrogenation or cycloaddition). However, an interesting alternative is that this species could be trapped by nitric oxide itself. According to <span id=\"cite_ITEM-29665-1\" name=\"citation\"><a href=\"#ITEM-29665-1\">[2]<\/a><\/span> in an article entitled &#8220;<em>Decomposition of nitric oxide at elevated pressures<\/em>&#8221; the rate of this termolecular reaction 3NO \u2192\u00a0N<sub>2<\/sub>O + NO<sub>2<\/sub> are said to obey third order kinetics.\u00a0One plausible mechanism for this process is shown below.<\/p>\n<p><a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/N3O3.svg\"><img decoding=\"async\" class=\"aligncenter size-full wp-image-29674\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/N3O3.svg\" alt=\"\" width=\"350\" \/><\/a><\/p>\n<p>So the question now arises as to whether this process would always intervene to prevent any trapping of species <strong>1<\/strong>. Time for some calculated energies.<span id=\"cite_ITEM-29665-2\" name=\"citation\"><a href=\"#ITEM-29665-2\">[3]<\/a><\/span> The reaction occurs in two steps,\u00a0<strong>TS1<\/strong>, forming <strong>Int<\/strong>, which then gives the product via\u00a0<strong>TS2<\/strong>. The combined IRC for these processes is shown below,<sup>\u2020<\/sup> and the \u00a0total energy barrier from <b>1<\/b> + NO for this process is small (~7 kcal\/mol).<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-29677\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/N3O3R_tot_ener.svg\" alt=\"\" width=\"500\" \/><\/p>\n<p>The NN bond length along the course of these two steps is shown below,<sup>\u2020<\/sup> indicting that it starts and ends with an ~N\u2261N bond, as implied in the scheme above.<\/p>\n<p><a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/35_14B.svg\"><img decoding=\"async\" class=\"aligncenter size-full wp-image-29686\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/35_14B.svg\" alt=\"\" width=\"500\" \/><\/a><\/p>\n<p>The dipole moment response is shown below.<sup>\u2020<\/sup><br \/>\n<a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/35_DM.svg\"><img decoding=\"async\" class=\"aligncenter size-full wp-image-29690\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/35_DM.svg\" alt=\"\" width=\"500\" \/><\/a><\/p>\n<p>Animation for the IRC for TS1 is shown below:<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-29680\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/TS1.gif\" alt=\"\" width=\"400\" \/><\/p>\n<p>The intermediate, N<sub>3<\/sub>O<sub>3<\/sub> has a spin density covering all six atoms (click on image below to see interactive 3D model) so is difficult to represent by <em>e.g.<\/em> a single valence bond structure as shown above.<br \/>\n<img decoding=\"async\" class=\"aligncenter size-full wp-image-29672\" onclick=\"jmolApplet([500,500],'load wp-content\/uploads\/2025\/09\/N3O2-spin.xyz;isosurface color green blue wp-content\/uploads\/2025\/09\/N3O2-spin.jvxl translucent;spin -5;set echo top left;font echo 16 serif bolditalic;color echo red; echo Spin density in N3O3;','c1');\"  src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/N3O2-spin.jpg\" alt=\"\" width=\"400\" \/><\/p>\n<p>The IRC for TS2 is animated below:<\/p>\n<p><img decoding=\"async\" class=\"aligncenter size-full wp-image-29682\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2025\/09\/TS2.gif\" alt=\"\" width=\"400\" \/><\/p>\n<p>The high value for \u0394G<sup>\u2021<\/sup> ~39.5 kcal\/mol arises in large part because of the loss of entropy in reducing three molecules to one at the transition states &#8211;\u00a0and can be compared with <em>e.g.<\/em> the value of \u0394G<sup>\u2021<\/sup>\u00a031.0 kcal\/mol previously quoted for the bimolecular dimerisation of two molecules of NO.<span id=\"cite_ITEM-29665-3\" name=\"citation\"><a href=\"#ITEM-29665-3\">[4]<\/a><\/span><\/p>\n<p>The story is not quite over yet, since other conformations for this reaction are still being explored. Currently it appears there is only a small free energy window between forming species <b>1<\/b> and it reacting further in the manner 3NO \u2192\u00a0N<sub>2<\/sub>O + NO<sub>2<\/sub> as shown above,\u00a0so it seems unlikely at this stage that <b>1<\/b> could be easily detected.<\/p>\n<hr \/>\n<p><sup>\u2020<\/sup> The slight discontinuity visible at ~IRC +1 is due to a conformational change between the end point of the IRC for <strong>TS1<\/strong> and the start point for <strong>TS2<\/strong>.<\/p>\n<hr \/>\n<p>DOI: <a href=\"https:\/\/doi.org\/10.59350\/rzepa.29665\" target=\"_blank\">10.59350\/rzepa.29665<\/a><\/p>\n<h2>References<\/h2>\n    <ol class=\"kcite-bibliography csl-bib-body\"><li id=\"ITEM-29665-0\">H. Rzepa, \"Hydrogenating the even more mysterious N\u2261N triple bond in a nitric oxide dimer.\", 2025. <a href=\"https:\/\/doi.org\/10.59350\/rzepa.29626\">https:\/\/doi.org\/10.59350\/rzepa.29626<\/a>\n\n<\/li>\n<li id=\"ITEM-29665-1\">T. Melia, \"Decomposition of nitric oxide at elevated pressures\", <i>Journal of Inorganic and Nuclear Chemistry<\/i>, vol. 27, pp. 95-98, 1965. <a href=\"https:\/\/doi.org\/10.1016\/0022-1902(65)80196-8\">https:\/\/doi.org\/10.1016\/0022-1902(65)80196-8<\/a>\n\n<\/li>\n<li id=\"ITEM-29665-2\">H. Rzepa, \"Alternative reactions of the N\u2261N triple bond in a nitric oxide dimer.\", 2025. <a href=\"https:\/\/doi.org\/10.14469\/hpc\/15549\">https:\/\/doi.org\/10.14469\/hpc\/15549<\/a>\n\n<\/li>\n<li id=\"ITEM-29665-3\">H. Rzepa, \"The even more mysterious N\u2261N triple bond in a nitric oxide dimer.\", 2025. <a href=\"https:\/\/doi.org\/10.59350\/rzepa.29429\">https:\/\/doi.org\/10.59350\/rzepa.29429<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> <!-- kcite-section 29665 -->","protected":false},"excerpt":{"rendered":"<p>In the previous post I mooted the possibility that a high energy form of the dimer of nitric oxide 1 might nonetheless be able to be detected using suitable traps (such as hydrogenation or cycloaddition). However, an interesting alternative is that this species could be trapped by nitric oxide itself. According to in an article [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"activitypub_content_warning":"","activitypub_content_visibility":"","activitypub_max_image_attachments":5,"activitypub_interaction_policy_quote":"anyone","activitypub_status":"federated","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[4],"tags":[],"ppma_author":[2661],"class_list":["post-29665","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.5 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Alternative reactions of the N\u2261N &quot;triple bond&quot; in a nitric oxide dimer: forming the trimer N3O3. - Henry Rzepa&#039;s Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29665\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Alternative reactions of the N\u2261N &quot;triple bond&quot; in a nitric oxide dimer: forming the trimer N3O3. - Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"og:description\" content=\"In the previous post I mooted the possibility that a high energy form of the dimer of nitric oxide 1 might nonetheless be able to be detected using suitable traps (such as hydrogenation or cycloaddition). However, an interesting alternative is that this species could be trapped by nitric oxide itself. According to in an article [&hellip;]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29665\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"article:published_time\" content=\"2025-09-03T10:25:18+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2025-09-03T10:29:43+00:00\" \/>\n<meta name=\"author\" content=\"Henry Rzepa\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Henry Rzepa\" \/>\n\t<meta name=\"twitter:label2\" content=\"Estimated reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"4 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"Alternative reactions of the N\u2261N \"triple bond\" in a nitric oxide dimer: forming the trimer N3O3. - Henry Rzepa&#039;s Blog","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29665","og_locale":"en_GB","og_type":"article","og_title":"Alternative reactions of the N\u2261N \"triple bond\" in a nitric oxide dimer: forming the trimer N3O3. - Henry Rzepa&#039;s Blog","og_description":"In the previous post I mooted the possibility that a high energy form of the dimer of nitric oxide 1 might nonetheless be able to be detected using suitable traps (such as hydrogenation or cycloaddition). 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in a nitric oxide dimer: forming the trimer N3O3."}]},{"@type":"WebSite","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/","name":"Henry Rzepa&#039;s Blog","description":"Chemistry with a twist","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-GB"},{"@type":"Person","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281","name":"Henry Rzepa","image":{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g370be3a7397865e4fd161aefeb0a5a85","url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","contentUrl":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","caption":"Henry Rzepa"},"description":"Henry Rzepa is Emeritus Professor of Computational Chemistry at Imperial College London.","sameAs":["https:\/\/orcid.org\/0000-0002-8635-8390"],"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?author=1"}]}},"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/pDef7-7It","jetpack-related-posts":[{"id":29626,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29626","url_meta":{"origin":29665,"position":0},"title":"Hydrogenating the even more mysterious N\u2261N triple bond in a nitric oxide dimer.","author":"Henry Rzepa","date":"August 25, 2025","format":false,"excerpt":"Previously I looked at some of the properties of the mysterious dimer of nitric oxide \u00a01 - not the known weak dimer but a higher energy form with a \"triple\" N\u2261N bond. This valence bond isomer of the weak dimer was some 24 kcal\/mol higher in free energy than the\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":29429,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29429","url_meta":{"origin":29665,"position":1},"title":"The even more mysterious N\u2261N triple bond in a nitric oxide dimer.","author":"Henry Rzepa","date":"August 18, 2025","format":false,"excerpt":"Previously, I pondered about the strange N=N double bond in nitrosobenzene dimer as a follow up to commenting on the curly arrow mechanism of the dimerisation. By the same curly arrow method, one can produce the below, showing how the simpler nitric oxide radical could potentially dimerise to a species\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":30890,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=30890","url_meta":{"origin":29665,"position":2},"title":"Valence bond representations with +ve charges on adjacent atoms? An odd titanium complex analysed.","author":"Henry Rzepa","date":"March 8, 2026","format":false,"excerpt":"A few posts back, I contemplated the curly arrows appropriate for the formation of nitrosobenzene dimer from nitrosobenzene, and commented on the odd nature of the N=N double bond formed in this process.. Odd, because the valence bond representation of this dimer (1 below) has two formally positive adjacent nitrogen\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":16208,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16208","url_meta":{"origin":29665,"position":3},"title":"Azane oxide, a tautomer of hydroxylamine.","author":"Henry Rzepa","date":"April 15, 2016","format":false,"excerpt":"In the previous post I described how hydronium hydroxide or H3O+...HO-, an intermolecular tautomer of water, has recently been observed captured inside an organic cage and how the free-standing species in water can be captured computationally with the help of solvating water bridges. Here I explore azane oxide or H3N+-O-,\u2021\u2026","rel":"","context":"In &quot;General&quot;","block_context":{"text":"General","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":8961,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8961","url_meta":{"origin":29665,"position":4},"title":"The mechanism of the Benzidine rearrangement.","author":"Henry Rzepa","date":"January 6, 2013","format":false,"excerpt":"The benzidine rearrangement is claimed to be an example of the quite rare\u00a0[5,5] sigmatropic migration, which is a ten-electron homologation of the very common [3,3] sigmatropic reaction (e.g. the Cope or Claisen). Some benzidine rearrangements are indeed thought to go through the [3,3] route. The topic has been reviewed here.\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"NCI surface. Click for  3D.","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/01\/benzidinenci.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":29383,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29383","url_meta":{"origin":29665,"position":5},"title":"The mysterious N=N double bond in nitrosobenzene dimer.","author":"Henry Rzepa","date":"August 11, 2025","format":false,"excerpt":"In an earlier blog, I discussed the curly arrows associated with the known dimerisation of nitrosobenzene, and how the\u00a0N=N double bond (shown in red below) forms in a single concerted process. One of the properties of this molecule is that the equilibrium between the monomer and dimer can be detected,\u2026","rel":"","context":"In &quot;Interesting chemistry&quot;","block_context":{"text":"Interesting chemistry","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=4"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"jetpack_likes_enabled":false,"authors":[{"term_id":2661,"user_id":1,"is_guest":0,"slug":"admin","display_name":"Henry Rzepa","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/897b6740f7f599bca7942cdf7d7914af5988937ae0e3869ab09aebb87f26a731?s=96&d=blank&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/29665","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=29665"}],"version-history":[{"count":20,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/29665\/revisions"}],"predecessor-version":[{"id":29701,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/29665\/revisions\/29701"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=29665"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=29665"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=29665"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=29665"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}