{"id":2707,"date":"2010-10-24T12:41:20","date_gmt":"2010-10-24T11:41:20","guid":{"rendered":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707"},"modified":"2011-04-15T11:35:54","modified_gmt":"2011-04-15T11:35:54","slug":"the-strongest-bond-in-the-universe","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707","title":{"rendered":"The strongest bond in the universe!"},"content":{"rendered":"
\n

The rather presumptious title assumes the laws and fundamental constants of physics are the same everywhere (they may not be<\/a>). With this constraint (and without yet defining what is meant by strongest), consider the three molecules:<\/p>\n\n\n\n\n\n\n\n\n
Property <\/p>\n

(CCSD\/aug-cc-pVTZ)<\/th>\n

N\u2261N<\/th>\n(H-N\u2261N)+<\/sup><\/th>\n(H-N\u2261N-H)2+<\/sup><\/th>\n<\/tr>\n
NN length, \u00c5<\/th>\n1.0967<\/a><\/td>\n1.0915<\/a><\/td>\n1.0795<\/a><\/td>\n<\/tr>\n
NN stretch, cm-1<\/sup><\/th>\n2418.8<\/td>\n2356.4 <\/p>\n

2545.1a<\/sup>\/2451.5<\/a>b<\/sup><\/td>\n

2226.3\/3024.0 <\/p>\n

2688.4a<\/sup>\/2567.7<\/a>b<\/sup><\/td>\n<\/tr>\n

ELF NN basin<\/p>\n

integration<\/th>\n

3.57<\/td>\n4.31<\/td>\n4.59<\/td>\n<\/tr>\n
QTAIM \u03c1(r)\/\u22072<\/sup>\u03c1(r)<\/th>\n0.714\/-3.38<\/td>\n0.690\/-3.07<\/td>\n0.700\/-2.96<\/td>\n<\/tr>\n
a<\/sup>Value for hydrogen mass of 10,000 b<\/sup>Value for hydrogen mass of 0.001.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The series explores the effect of protonating dinitrogen (generally considered as strong as a diatomic bond gets).<\/p>\n

    \n
  1. Firstly, one notes that the N-N distance decreases with mono and then diprotonation, the second protonation having the greater effect. Is shorter stronger<\/a>?<\/li>\n
  2. What about the NN stretching vibration? Here one encounters an annoying feature of vibrations; the modes are not always pure. Thus whilst in N2<\/sub> itself, there is only one normal mode, and it is as pure as they get, by the time we have di-protonated, we have three stretching modes, two involving H-N and one N-N. They mix and none can now be considered a pure N-N stretch. Thus in H2<\/sub>N2<\/sub>, the highest wavenumber mode of 3024 is a mixture of H-N and N-N, and likewise the 2226 mode, albeit in different proportions. So a trick has to be played. If the mass of each hydrogen is increased to 10,000, modes involving these super-heavy atoms no longer mix with any other mode. Now, the N-N mode becomes pure, and its value is 2688, a significant increase on nitrogen itself. The monoprotonated form also shows a lesser increase.<\/li>\n
  3. The ELF disynaptic basins for the three molecules also steadily increase their populations. Electrons that were previously in the terminal nitrogen lone pairs now creep into the N-N region instead, and hence make the bond stronger. The population does not reach six (the nominal value for a triple bond), since the H-N regions still contain more than 2 electrons. But ELF matches the previous two results.<\/li>\n
  4. QTAIM measures the electron density \u03c1(r) at the bond critical point. Here different behaviour is seen, with \u03c1(r) lower for the monprotonated, and the diprotonated form intermediate between the other two. Perhaps absolute electron densities measured at a single point do not measure bnd strengths after all. The Laplacian, \u22072<\/sup>\u03c1(r) steadily decreases along the series.<\/li>\n<\/ol>\n

    So is the NN bond in HNNH2+<\/sup> the strongest bond in the universe? Almost certainly. OK, so bonds with higher formal bond orders (Cr2<\/sub> for example) exist, but they come nowhere near HN\u2261NH2+<\/sup>, which is crowned champion.<\/p>\n

    Oh, by \u00a0the way, another article (DOI: 10.1063\/1.1576756<\/a>) claimed the title in 2003, \u00a0but \u00a0I make the claim for a stronger bond here!<\/p>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    The rather presumptious title assumes the laws and fundamental constants of physics are the same everywhere (they may not be). With this constraint (and without yet defining what is meant by strongest), consider the three molecules: Property  (CCSD\/aug-cc-pVTZ) N\u2261N (H-N\u2261N)+ (H-N\u2261N-H)2+ NN length, \u00c5 1.0967 1.0915 1.0795 NN stretch, cm-1 2418.8 2356.4  2545.1a\/2451.5b 2226.3\/3024.0  2688.4a\/2567.7b […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_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":"","footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[4],"tags":[2648],"ppma_author":[2661],"class_list":["post-2707","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-interesting-chemistry"],"yoast_head":"\nThe strongest bond in the universe! - Henry Rzepa'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=2707\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"The strongest bond in the universe! - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"The rather presumptious title assumes the laws and fundamental constants of physics are the same everywhere (they may not be). With this constraint (and without yet defining what is meant by strongest), consider the three molecules: Property  (CCSD\/aug-cc-pVTZ) N\u2261N (H-N\u2261N)+ (H-N\u2261N-H)2+ NN length, \u00c5 1.0967 1.0915 1.0795 NN stretch, cm-1 2418.8 2356.4  2545.1a\/2451.5b 2226.3\/3024.0  2688.4a\/2567.7b […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2010-10-24T11:41:20+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2011-04-15T11:35:54+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=\"2 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"The strongest bond in the universe! - Henry Rzepa'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=2707","og_locale":"en_GB","og_type":"article","og_title":"The strongest bond in the universe! - Henry Rzepa's Blog","og_description":"The rather presumptious title assumes the laws and fundamental constants of physics are the same everywhere (they may not be). With this constraint (and without yet defining what is meant by strongest), consider the three molecules: Property  (CCSD\/aug-cc-pVTZ) N\u2261N (H-N\u2261N)+ (H-N\u2261N-H)2+ NN length, \u00c5 1.0967 1.0915 1.0795 NN stretch, cm-1 2418.8 2356.4  2545.1a\/2451.5b 2226.3\/3024.0  2688.4a\/2567.7b […]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707","og_site_name":"Henry Rzepa's Blog","article_published_time":"2010-10-24T11:41:20+00:00","article_modified_time":"2011-04-15T11:35:54+00:00","author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"2 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"The strongest bond in the universe!","datePublished":"2010-10-24T11:41:20+00:00","dateModified":"2011-04-15T11:35:54+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707"},"wordCount":446,"commentCount":7,"keywords":["Interesting chemistry"],"articleSection":["Interesting chemistry"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707","name":"The strongest bond in the universe! - Henry Rzepa's Blog","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website"},"datePublished":"2010-10-24T11:41:20+00:00","dateModified":"2011-04-15T11:35:54+00:00","author":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"breadcrumb":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707"]}]},{"@type":"BreadcrumbList","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=2707#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog"},{"@type":"ListItem","position":2,"name":"The strongest bond in the universe!"}]},{"@type":"WebSite","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/","name":"Henry Rzepa'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-HF","jetpack-related-posts":[{"id":22378,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=22378","url_meta":{"origin":2707,"position":0},"title":"The strongest bond in the universe: revisited ten years on.","author":"Henry Rzepa","date":"May 23, 2020","format":false,"excerpt":"I occasionally notice that posts that first appeared here many years ago suddenly attract attention. Thus this post, entitled The strongest bond in the universe, from ten years back, has suddently become the most popular, going from an average of 0-2 hits per day to 92 in a single day\u2026","rel":"","context":"In "Interesting chemistry"","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":22391,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=22391","url_meta":{"origin":2707,"position":1},"title":"The strongest bond in the universe: A crystallographic reality check?","author":"Henry Rzepa","date":"May 25, 2020","format":false,"excerpt":"My previous two posts on the topic of strongest bonds have involved mono and diprotonating N2 and using quantum mechanics to predict the effect this has on the N-N bond via its length and vibrational stetching mode. Such species are very unlikely to be easily observed for verification. But how\u2026","rel":"","context":"In "crystal_structure_mining"","block_context":{"text":"crystal_structure_mining","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1745"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2020\/05\/Screenshot-33-1024x714.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":9105,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9105","url_meta":{"origin":2707,"position":2},"title":"The Benzidine rearrangement. Computed kinetic isotope effects.","author":"Henry Rzepa","date":"January 11, 2013","format":false,"excerpt":"Kinetic isotope effects have become something of a lost art when it comes to exploring reaction mechanisms. But in their heyday they were absolutely critical for establishing the mechanism of the benzidine rearrangement. This classic mechanism proceeds via bisprotonation of diphenyl hydrazine, but what happens next was the crux. Does\u2026","rel":"","context":"In "Interesting chemistry"","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":2707,"position":3},"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 "Interesting chemistry"","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":2707,"position":4},"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 "Interesting chemistry"","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":29665,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=29665","url_meta":{"origin":2707,"position":5},"title":"Alternative reactions of the N\u2261N “triple bond” in a nitric oxide dimer: forming the trimer N3O3.","author":"Henry Rzepa","date":"September 3, 2025","format":false,"excerpt":"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.\u2026","rel":"","context":"In "Interesting chemistry"","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\/2707","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=2707"}],"version-history":[{"count":0,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/2707\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2707"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2707"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2707"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=2707"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}