{"id":16208,"date":"2016-04-15T10:03:45","date_gmt":"2016-04-15T09:03:45","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=16208"},"modified":"2016-04-15T10:03:45","modified_gmt":"2016-04-15T09:03:45","slug":"azane-oxide-a-tautomer-of-hydroxylamine","status":"publish","type":"post","link":"https:\/\/www.rzepa.net\/blog\/?p=16208","title":{"rendered":"Azane oxide, a tautomer of hydroxylamine."},"content":{"rendered":"
\n

\n\tIn the previous post<\/a> I described how hydronium hydroxide or H3<\/sub>O<\/font>+<\/sup>…HO–<\/sup>, an intermolecular tautomer of water, has recently been observed captured inside an organic cage[1]<\/a><\/span> and how the free-standing species in water can be captured computationally with the help of solvating water bridges. Here I explore azane oxide<\/strong> or H3<\/sub>N+<\/sup>-O–<\/sup><\/span>,‡<\/sup> a tautomer of the better known hydroxylamine (H2<\/sub>N-OH<\/span>).\n<\/p>\n

\n\tThe usual search[2]<\/a><\/span> of the Cambridge structure database reveals only two (related) entries[3]<\/a><\/span>,[4]<\/a><\/span> the second reported in 2015.[5]<\/a><\/span>.\n<\/p>\n

\n\t\"NH3-8\"
\n\t\"NH3-8\"\n<\/p>\n

\n\tNow, location of hydrogen atoms is always a bit tricky, but here we see two species H3<\/sub>N+<\/sup>-OH…–<\/sup>O-+<\/sup>NH3<\/sub> connected by a strong hydrogen bond of 1.54Å (click on the above image to see this packing). However, it is noteworthy that the N-O bonds for each of these species are exactly the same length (1.412Å); one might have imagined that whether the oxygen carries a proton or not would affect its bond length to nitrogen. There is here a strong hint that energetically the azane oxide might be relatively low in energy relative to hydroxylamine and perhaps that the zwitterionic form might be favoured when captured with hydrogen bonds.\n<\/p>\n

\n\tSo certainly time for a computational exploration of this species. I am using the three water bridges as before, each comprised of three water molecules and the ωB97XD\/6-311++G(d,p)\/SCRF=water method. In fact the structure optimises[6]<\/a><\/span> to a delightful propeller-like geometry in which bridges are formed from both two AND three waters across the ion-pair, with overall three-fold C3<\/sub> symmetry (i.e. chiral! Indeed, this species has a predicted optical rotation of 40° at 589nm).\n<\/p>\n

\n\t\"NH3-8\"\n<\/p>\n

\n\tHydroxylamine itself has a less symmetric arrangement of hydrogen bonds[7]<\/a><\/span>, with a free energy in fact very similar (within 1 kcal\/mol) to the ion-pair isomer. Here, a stochastic (statistical) exploration of all the various arrangements of water would be needed to be confident that the lowest energy form had been located. I would note that the N-O bond lengths in the ion-pair and neutral forms are respectively 1.399 and 1.435Å.\n<\/p>\n

\n\t\"NH3-8\"\n<\/p>\n

\n\tCertainly, this very brief computational look at azane oxide<\/strong><\/span> suggests that concentrations of this species in aqueous solutions of hydroxylamine might be appreciable (detectable). Its "trapping" inside a suitably designed cavity must be a realistic possibility (the cavity used to trap hydronium hydroxide probably does not have the correct dimensions for this purpose), as indeed illustrated in the two crystal structures noted above.\n<\/p>\n

\n

\n\t‡<\/sup> I have represented this species in ionic form, but you may find text books showing it in dative form, or H3<\/sub>N→O. My personal inclination is to always prefer the ionic form, if only because it enables connections\/analogies such as the one here to hydronium hydroxide to be more easily made.<\/p>\n

References<\/h2>\n
  1. M. Stapf, W. Seichter, and M. Mazik, \"Unique Hydrogen\u2010Bonded Complex of Hydronium and Hydroxide Ions\", Chemistry \u2013 A European Journal<\/i>, vol. 21, pp. 6350-6354, 2015. https:\/\/doi.org\/10.1002\/chem.201406383<\/a>\n\n<\/li>\n
  2. H. Rzepa, \"Search for Azane oxide\", 2016. https:\/\/doi.org\/10.14469\/hpc\/380<\/a>\n\n<\/li>\n
  3. Fischer, Dennis., Klapotke, Thomas M.., and Stierstorfer, Jorg., \"CCDC 1054611: Experimental Crystal Structure Determination\", 2015. https:\/\/doi.org\/10.5517\/cc14ddqn<\/a>\n\n<\/li>\n
  4. Fischer, D.., Klapotke, T.M.., and Stierstorfer, J.., \"CCDC 827687: Experimental Crystal Structure Determination\", 2012. https:\/\/doi.org\/10.5517\/ccws8lh<\/a>\n\n<\/li>\n
  5. D. Fischer, T.M. Klap\u00f6tke, and J. Stierstorfer, \"1,5\u2010Di(nitramino)tetrazole: High Sensitivity and Superior Explosive Performance\", Angewandte Chemie International Edition<\/i>, vol. 54, pp. 10299-10302, 2015. https:\/\/doi.org\/10.1002\/anie.201502919<\/a>\n\n<\/li>\n
  6. H.S. Rzepa, \"H 21 N 1 O 10\", 2016. https:\/\/doi.org\/10.14469\/ch\/192000<\/a>\n\n<\/li>\n
  7. H.S. Rzepa, \"H 21 N 1 O 10\", 2016. https:\/\/doi.org\/10.14469\/ch\/192001<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    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–,‡ a tautomer of the better […]<\/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,"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":[4,6],"tags":[1684,503,1622,1576,164,1453,1459,1797,1718,1798,1799,1590,1738,1827,1833],"class_list":["post-16208","post","type-post","status-publish","format-standard","hentry","category-general","category-interesting-chemistry","tag-ammonia","tag-aqueous-solutions","tag-bases","tag-energy-relative","tag-free-energy","tag-functional-groups","tag-hydrogen-bond","tag-hydronium","tag-hydroxides","tag-hydroxyl","tag-hydroxylamine","tag-lowest-energy-form","tag-properties-of-water","tag-reducing-agents","tag-self-ionization-of-water"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p1gPyz-4dq","jetpack_likes_enabled":true,"_links":{"self":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/16208","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=16208"}],"version-history":[{"count":0,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=\/wp\/v2\/posts\/16208\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=16208"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=16208"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rzepa.net\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=16208"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}