{"id":9659,"date":"2013-03-03T11:49:30","date_gmt":"2013-03-03T11:49:30","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=9659"},"modified":"2014-01-17T07:35:30","modified_gmt":"2014-01-17T07:35:30","slug":"understanding-the-electrophilic-aromatic-substitution-of-indole","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659","title":{"rendered":"Understanding the electrophilic aromatic substitution of indole."},"content":{"rendered":"
\n

The electrophilic substitution of indoles is a staple of any course on organic chemistry. Indoles also hold a soft-spot for me, since I synthesized not a few as part of my Ph.D. studies.[1]<\/a><\/span>,[2]<\/a><\/span> The preference for substitution in the 3-position is normally explained using the arrows shown below (position 3=green,2=blue,1=red). Here I explore how these arrows might be interpreted in terms of various quantum mechanical properties.<\/p>\n

\"indole\"<\/p>\n

I have elsewhere in these posts shown how NBO (natural bond orbitals) can often be used to probe donor-acceptor interactions in molecules. Can it be applied to indole (as donor) interacting with an electrophile (as acceptor) in order to predict where the most nucleophilic centre is? The law is that the pair of such filled\/empty orbitals with the lowest energy gap will predict the reactivity. Since the electrophile E is common, we might presume that the NBO donor orbital with the highest energy is the relevant predictor. Well, this emerges as the NBO describing the 8,9 bond; it is not any of those shown above! The next NBO in energy is also located on the benzo group. Only the 3rd-highest NBO corresponds to the red arrows above. In fact the NBO with the least-favourable<\/em> energy is the one that maps to positions 2 or 3, those normally implicated in the reactions of this molecule. What has gone wrong?<\/p>\n\n\n\n\n
\n
\"Click

E=-0.2910au.
Click for 3D<\/p><\/div>\n<\/td>\n

\n
\"Click

E=-0.3107au.
Click for 3D<\/p><\/div>\n<\/td>\n<\/tr>\n

\n
\"Click

E=-0.3113au.
Click for 3D<\/p><\/div>\n<\/td>\n

\n
\"Click

E=-0.3142au.
Click for 3D<\/p><\/div>\n<\/td>\n

\n
\"Click

E=-0.3335au.
Click for 3D<\/p><\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

To start understanding, we must review the assumptions made in the above analysis.<\/p>\n

    \n
  1. Firstly, we need to distinguish between local<\/strong> and global<\/strong> properties of molecules. A local property is one e.g. associated perhaps with an atom or bond. A global property might be the aromaticity<\/strong> of the system as a whole. The NBO analysis, by definition, tries to localise the wavefunction to one or two centres. This means that it reduces a six-electron aromatic ring to three two-centre bonds. But breaking up an aromatic ring may not be the best way of looking at the problem. In this case, the 2,3 N=C bond emerges as the most stable double bond, largely because the six electrons of the benzo group are delocalised and hence not so stable locally! So too much localisation can throw the baby away with the bath water. So let us try a rather more global property, the molecular electrostatic potential (MEP):
    \n
    \"Molecular

    Molecular electrostatic potential. Click for 3D.<\/p><\/div><\/p>\n

    This probes the molecule for regions which are the most attractive to a proton (=E+<\/sup>). Perhaps surprisingly, the benzo group still emerges as the most attractive region, but at least there is a small attractive finger (green) that reaches out to the 3-position rather than the 2-position (the “right” answer). It is not entirely convincing though, is it?<\/p>\n<\/li>\n

  2. Which leads us on to another assumption, which invokes Hammond’s postulate<\/a> that the transition state for the reaction will resemble the stable species nearest to it in free energy. What if the transition state (which is what determines the rate of a reaction) more closely resembles the (initial) product of this reaction, the so-called<\/a> Wheland intermediate<\/a> rather than indole itself? I am going to calculate this intermediate in a novel manner; as an ion-pair resulting from reaction of indole with HCl in methanol (I have blogged elsewhere that I regard it as lazy to simple add a proton and put +1 as the overall charge of the system). So here are the relative free energies of indole reacted with HCl in respectively the 1,2 and 3 positions: 4.1<\/a>, 10.0<\/a>, 0.0<\/a>\u00a0kcal\/mol.The relatively high energy of the 2-substituted intermediate reflects its loss of global<\/em> aromaticity compared to the other two, rather than necessarily any local property.\u00a0
    \n
    \"3-Wheland

    3-Wheland intermediate. Click for 3D.<\/p><\/div><\/p>\n

    We might therefore conclude that one should not seek evidence in the wavefunction\u00a0of indole itself\u00a0for the preference for green rather than blue or red arrows as shown above, but in a reaction product which best reflects the global properties such as aromaticity.<\/p>\n<\/li>\n

  3. One could go one stage further and actually locate explicit transition states for the three isomeric reactions, as was done here<\/a>. I may report back on this in the future.<\/li>\n<\/ol>\n

    I set out these approaches aware that a subject is often taught by reducing it to rules (heuristics) which one then hopes are transferable between different molecules with common local or global features. One does not want to reduce it down merely to numbers computed from a wave equation. But one should also remember that whilst arrow-pushing may be fine for relatively simple systems, it may not be robust towards increasing complexity (i.e.<\/em> multiple substituents around the ring). At some stage, one will have to take the decision to augment the simple heuristics with computed numbers. Deciding when to do so will be one of the challenges facing the teaching of chemistry over the next decade.<\/p>\n

    References<\/h2>\n
    1. B.C. Challis, and H.S. Rzepa, \"The mechanism of diazo-coupling to indoles and the effect of steric hindrance on the rate-limiting step\", Journal of the Chemical Society, Perkin Transactions 2<\/i>, pp. 1209, 1975. https:\/\/doi.org\/10.1039\/p29750001209<\/a>\n\n<\/li>\n
    2. B.C. Challis, and H.S. Rzepa, \"Heteroaromatic hydrogen exchange reactions. Part 9. Acid catalysed decarboxylation of indole-3-carboxylic acids\", Journal of the Chemical Society, Perkin Transactions 2<\/i>, pp. 281, 1977. https:\/\/doi.org\/10.1039\/p29770000281<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

      The electrophilic substitution of indoles is a staple of any course on organic chemistry. Indoles also hold a soft-spot for me, since I synthesized not a few as part of my Ph.D. studies., The preference for substitution in the 3-position is normally explained using the arrows shown below (position 3=green,2=blue,1=red). Here I explore how these […]<\/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":"","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":[1006,24,1004,1005,843,1007,373],"ppma_author":[2661],"class_list":["post-9659","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-benzo","tag-energy","tag-least-favourable-energy","tag-lowest-energy-gap","tag-reaction-mechanism","tag-reaction-product","tag-tutorial-material"],"yoast_head":"\nUnderstanding the electrophilic aromatic substitution of indole. - 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=9659\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Understanding the electrophilic aromatic substitution of indole. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"The electrophilic substitution of indoles is a staple of any course on organic chemistry. Indoles also hold a soft-spot for me, since I synthesized not a few as part of my Ph.D. studies., The preference for substitution in the 3-position is normally explained using the arrows shown below (position 3=green,2=blue,1=red). Here I explore how these […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2013-03-03T11:49:30+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2014-01-17T07:35:30+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/indole1.svg\" \/>\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":"Understanding the electrophilic aromatic substitution of indole. - 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=9659","og_locale":"en_GB","og_type":"article","og_title":"Understanding the electrophilic aromatic substitution of indole. - Henry Rzepa's Blog","og_description":"The electrophilic substitution of indoles is a staple of any course on organic chemistry. Indoles also hold a soft-spot for me, since I synthesized not a few as part of my Ph.D. studies., The preference for substitution in the 3-position is normally explained using the arrows shown below (position 3=green,2=blue,1=red). Here I explore how these […]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659","og_site_name":"Henry Rzepa's Blog","article_published_time":"2013-03-03T11:49:30+00:00","article_modified_time":"2014-01-17T07:35:30+00:00","og_image":[{"url":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/indole1.svg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"4 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"Understanding the electrophilic aromatic substitution of indole.","datePublished":"2013-03-03T11:49:30+00:00","dateModified":"2014-01-17T07:35:30+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659"},"wordCount":884,"commentCount":2,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/indole1.svg","keywords":["benzo","energy","least-favourable energy","lowest energy gap","Reaction Mechanism","reaction product","Tutorial material"],"articleSection":["Interesting chemistry"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659","name":"Understanding the electrophilic aromatic substitution of indole. - Henry Rzepa's Blog","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#website"},"primaryImageOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659#primaryimage"},"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/indole1.svg","datePublished":"2013-03-03T11:49:30+00:00","dateModified":"2014-01-17T07:35:30+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=9659#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659"]}]},{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659#primaryimage","url":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/indole1.svg","contentUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/indole1.svg"},{"@type":"BreadcrumbList","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9659#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog"},{"@type":"ListItem","position":2,"name":"Understanding the electrophilic aromatic substitution of indole."}]},{"@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\/pDef7-2vN","jetpack-related-posts":[{"id":12056,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12056","url_meta":{"origin":9659,"position":0},"title":"The mechanism of diazo coupling: more hidden mechanistic intermediates.","author":"Henry Rzepa","date":"March 8, 2014","format":false,"excerpt":"The diazo-coupling reaction dates back to the 1850s (and a close association with Imperial College via the first professor of chemistry there, August von Hofmann) and its mechanism was much studied in the heyday of physical organic chemistry. Nick Greeves, purveyor of the excellent ChemTube3D site, contacted me about the\u2026","rel":"","context":"In "reaction mechanism"","block_context":{"text":"reaction mechanism","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=1086"},"img":{"alt_text":"cis-diazo","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/03\/cis-diazo.gif?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":9706,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=9706","url_meta":{"origin":9659,"position":1},"title":"Kinetic vs Thermodynamic control. Subversive thoughts for electrophilic substitution of Indole.","author":"Henry Rzepa","date":"March 10, 2013","format":false,"excerpt":"I mentioned in the last post that one can try to predict the outcome of electrophilic aromatic substitution by approximating the properties of the transition state from those of either the reactant or the (presumed Wheland) intermediate by invoking Hammond's postulate. A third option is readily available nowadays; calculate the\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":"Click for 3D.","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2013\/03\/3-NO-indole-ESP.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":16563,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=16563","url_meta":{"origin":9659,"position":2},"title":"Exploring the electrophilic directing influence of heteroaromatic rings using crystal structure data mining.","author":"Henry Rzepa","date":"June 21, 2016","format":false,"excerpt":"This is a follow-up to the post on\u00a0exploring the directing influence of (electron donating) substituents on benzene with the focus on heteroaromatic rings such indoles, pyrroles and group 16 analogues (furans, thiophenes etc). The search query is shown above\u00a0(and is available here). As before, the distance is compared\u00a0from an electrophile,\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":"","width":0,"height":0},"classes":[]},{"id":15415,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=15415","url_meta":{"origin":9659,"position":3},"title":"I\u2019ve started so I\u2019ll finish. The ionisation mechanism and kinetic isotope effects for 1,3-dimethylindolin-2 one","author":"Henry Rzepa","date":"January 7, 2016","format":false,"excerpt":"This is the third and final study deriving from my Ph.D.. The first two topics dealt with the mechanism of heteroaromatic electrophilic attack using either a diazonium cation or a proton as electrophile, followed by either proton abstraction or carbon dioxide loss from the resulting Wheland intermediate. This final study\u2026","rel":"","context":"In "Historical"","block_context":{"text":"Historical","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?cat=565"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":15395,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=15395","url_meta":{"origin":9659,"position":4},"title":"I\u2019ve started so I\u2019ll finish. Kinetic isotope effect models for a general acid as a catalyst in the protiodecarboxylation of indoles.","author":"Henry Rzepa","date":"January 10, 2016","format":false,"excerpt":"Earlier I explored models for the heteroaromatic electrophilic protiodecarboxylation of an 3-substituted indole, focusing on the role of water as the proton transfer and delivery agent. Next, came\u00a0models for both water and the general base catalysed\u00a0ionization of indolinones. Here I\u00a0explore\u00a0general acid\u00a0catalysis by evaluating the properties of two possible models for\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":12115,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=12115","url_meta":{"origin":9659,"position":5},"title":"Aromatic electrophilic substitution. A different light on the bromination of benzene.","author":"Henry Rzepa","date":"March 12, 2014","format":false,"excerpt":"My previous post related to the aromatic electrophilic substitution of benzene using as electrophile phenyl diazonium chloride. Another prototypical reaction, and again one where benzene is too inactive for the reaction to occur easily, is the catalyst-free bromination of benzene to give bromobenzene and HBr.\u00a0 The \"text-book\" mechanism involves nucleophilic\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":"br2+benzene","src":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2014\/03\/br2+benzene.svg","width":350,"height":200},"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\/9659","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=9659"}],"version-history":[{"count":24,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/9659\/revisions"}],"predecessor-version":[{"id":11923,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/9659\/revisions\/11923"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=9659"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=9659"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=9659"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=9659"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}