{"id":8508,"date":"2012-12-03T15:12:41","date_gmt":"2012-12-03T15:12:41","guid":{"rendered":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=8508"},"modified":"2012-12-08T08:00:48","modified_gmt":"2012-12-08T08:00:48","slug":"the-mechanism-of-the-birch-reduction-part-2","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508","title":{"rendered":"The mechanism of the Birch reduction. Part 2: a transition state model."},"content":{"rendered":"
\n

I promised that the follow-up to on the topic of Birch reduction would focus on the proton transfer reaction between the radical anion of anisole and a proton source, as part of analysing whether the mechanistic pathway proceeds O<\/strong><\/span> or M<\/span><\/strong>.<\/p>\n

\"\"<\/p>\n

To add some context, Hammond’s postulate<\/a>\u00a0[1]<\/a><\/span>\u00a0states that “the structure of a transition state resembles that of the species nearest to it in\u00a0free energy<\/em>.” If the structure of the transition state for proton transfer above resembles that of the radical anion precursor we would call this an early transition state and it would be a reasonable approximation to infer properties of the reaction from the properties of that radical anion. The previous post<\/a> explored those properties via<\/em> the computed molecular electrostatic potential (MEP) and the highest energy NBO (natural bond orbitals, which are used here instead of molecular orbitals). Unfortunately, they did not agree with each other. Remember that Hammond’s postulate dates from 1955, an era when it was not practical to compute the structure of a transition state directly using quantum mechanics (certainly not so for such a complex reaction as that shown above). Indeed, one might argue that such a structure has only become computable in a practical sense very recently! As I showed previously, the radical ion-pair resulting from a 1-electron transfer from sodium to anisole has a dipole moment of ~11.6D, and the reaction is conducted in a solvent of medium polarity. This combination means that one really is obliged to take into account the dielectric of the solvent, and indeed any strong explicit hydrogen bonds that might be present. The codes for doing this have really only recently become robust enough to tackle such an endeavour[2]<\/a><\/span>, which might explain why such calculations are not yet abundant, or ubiquitously cited in the text books.<\/p>\n

\"\"

Proton transfer for M mechanism. Click for 3D.<\/p><\/div>\n

The proton transfer via one\u00a0M<\/strong><\/span> mechanism<\/a> is shown above. The proton source is ammonia, which is known from experiment to lead to sluggish reactions (the more acidic t-butanol is often added to speed up the reaction), but we can see that the transition state is very late, \u03bdi<\/sub>\u00a0423.8 cm-1<\/sup>. The N…H bond is largely broken, and the C-H bond is mostly formed. The dipole moment is 7.7D, also different from that of the reactant. Perhaps, knowing this, it is not too surprising that inferences based on Hammond’s postulate as applied to the reactant are not reliable. The value of\u00a0\u0394G\u2020<\/sup>298<\/sub>computed from this model is 22.8 kcal\/mol, which is on the high-ish side for a reaction to occur readily at room temperatures or below.[3]<\/a><\/span>\u00a0This nevertheless nicely conforms what we already know, that a more acidic proton donor is needed to achieve a fast reaction.<\/p>\n

\"\"

Proton transfer for O mechanism. Click for 3D.<\/p><\/div>\n

The proton transfer via<\/em>\u00a0one\u00a0O<\/strong><\/span> mechanism<\/a> is similar, but a tad less “late”. This already raises doubts about application of Hammond’s postulate to this system; one cannot really compare two reactions in which each reactant differs in its resemblance to its transition state. The dipole moment of this alternative transition state is also 7.7D, but the transition imaginary mode is much higher at \u03bdi<\/sub> 869 cm-1<\/sup>. The free energy barrier is 21.0, some\u00a01.8 kcal\/mol<\/strong> lower than the barrier for the M<\/strong> mechanism. This corresponds to a rate about 21 times faster for O over M (at 298K).<\/p>\n

To conclude, we characterise two (of the four) isomeric transition states for protonation of the radical anion intermediate in the Birch reduction of anisole. These two transition states are actually different in several subtle regards, differences which would not have manifested if only the properties of the reactant had been considered. The final word must be that the text books are likely correct on this one, although a little more work is still needed to tidy up loose ends. \u00a0<\/p>\n

References<\/h2>\n
  1. G.S. Hammond, \"A Correlation of Reaction Rates\", Journal of the American Chemical Society<\/i>, vol. 77, pp. 334-338, 1955. https:\/\/doi.org\/10.1021\/ja01607a027<\/a>\n\n<\/li>\n
  2. J. Kong, P.V.R. Schleyer, and H.S. Rzepa, \"Successful Computational Modeling of Isobornyl Chloride Ion-Pair Mechanisms\", The Journal of Organic Chemistry<\/i>, vol. 75, pp. 5164-5169, 2010. https:\/\/doi.org\/10.1021\/jo100920e<\/a>\n\n<\/li>\n
  3. H.E. Zimmerman, and P.A. Wang, \"Regioselectivity of the Birch reduction\", Journal of the American Chemical Society<\/i>, vol. 112, pp. 1280-1281, 1990. https:\/\/doi.org\/10.1021\/ja00159a078<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    I promised that the follow-up to on the topic of Birch reduction would focus on the proton transfer reaction between the radical anion of anisole and a proton source, as part of analysing whether the mechanistic pathway proceeds O or M. To add some context, Hammond’s postulate\u00a0\u00a0states that “the structure of a transition state resembles […]<\/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":[],"tags":[951,431,24,40,206,950,397,843,373],"ppma_author":[2661],"class_list":["post-8508","post","type-post","status-publish","format-standard","hentry","tag-birch-reduction","tag-dielectric","tag-energy","tag-free-energy","tag-free-energy-barrier","tag-hammonds-postulate","tag-proton-transfer","tag-reaction-mechanism","tag-tutorial-material"],"yoast_head":"\nThe mechanism of the Birch reduction. Part 2: a transition state model. - 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=8508\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"The mechanism of the Birch reduction. Part 2: a transition state model. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"I promised that the follow-up to on the topic of Birch reduction would focus on the proton transfer reaction between the radical anion of anisole and a proton source, as part of analysing whether the mechanistic pathway proceeds O or M. To add some context, Hammond’s postulate\u00a0\u00a0states that “the structure of a transition state resembles […]\" \/>\n<meta property=\"og:url\" content=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508\" \/>\n<meta property=\"og:site_name\" content=\"Henry Rzepa's Blog\" \/>\n<meta property=\"article:published_time\" content=\"2012-12-03T15:12:41+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2012-12-08T08:00:48+00:00\" \/>\n<meta property=\"og:image\" content=\"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/birch.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=\"3 minutes\" \/>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"The mechanism of the Birch reduction. Part 2: a transition state model. - 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=8508","og_locale":"en_GB","og_type":"article","og_title":"The mechanism of the Birch reduction. Part 2: a transition state model. - Henry Rzepa's Blog","og_description":"I promised that the follow-up to on the topic of Birch reduction would focus on the proton transfer reaction between the radical anion of anisole and a proton source, as part of analysing whether the mechanistic pathway proceeds O or M. To add some context, Hammond’s postulate\u00a0\u00a0states that “the structure of a transition state resembles […]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508","og_site_name":"Henry Rzepa's Blog","article_published_time":"2012-12-03T15:12:41+00:00","article_modified_time":"2012-12-08T08:00:48+00:00","og_image":[{"url":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/birch.svg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"3 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"The mechanism of the Birch reduction. Part 2: a transition state model.","datePublished":"2012-12-03T15:12:41+00:00","dateModified":"2012-12-08T08:00:48+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508"},"wordCount":678,"commentCount":2,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/birch.svg","keywords":["Birch reduction","dielectric","energy","free energy","free energy barrier","Hammonds postulate","proton transfer","Reaction Mechanism","Tutorial material"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508","name":"The mechanism of the Birch reduction. Part 2: a transition state model. - 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=8508#primaryimage"},"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508#primaryimage"},"thumbnailUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/birch.svg","datePublished":"2012-12-03T15:12:41+00:00","dateModified":"2012-12-08T08:00:48+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=8508#breadcrumb"},"inLanguage":"en-GB","potentialAction":[{"@type":"ReadAction","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508"]}]},{"@type":"ImageObject","inLanguage":"en-GB","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508#primaryimage","url":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/birch.svg","contentUrl":"http:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/birch.svg"},{"@type":"BreadcrumbList","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8508#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog"},{"@type":"ListItem","position":2,"name":"The mechanism of the Birch reduction. Part 2: a transition state model."}]},{"@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\/pDef7-2de","jetpack-related-posts":[{"id":8540,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8540","url_meta":{"origin":8508,"position":0},"title":"The mechanism of the Birch reduction. Part 3: reduction of benzene","author":"Henry Rzepa","date":"December 4, 2012","format":false,"excerpt":"Birch reduction of benzene itself results in 1,4-cyclohexadiene rather than the more stable (conjugated) 1,3-cyclohexadiene. Why is this? The mechanism, as elaborated in the previous two posts, involves a one-electron transfer from a sodium atom to form the radical anion, which is then protonated in a second step, and this\u2026","rel":"","context":"In \"Birch reduction\"","block_context":{"text":"Birch reduction","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=birch-reduction"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/birch-ip.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":8452,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8452","url_meta":{"origin":8508,"position":1},"title":"The mechanism of the Birch reduction. Part 1: reduction of anisole.","author":"Henry Rzepa","date":"December 1, 2012","format":false,"excerpt":"The Birch reduction is a classic method for partially reducing e.g. aryl ethers using electrons (from sodium dissolved in ammonia) as the reductant rather than e.g. dihydrogen. As happens occasionally in chemistry, a long debate broke out over the two alternative mechanisms labelled O (for ortho protonation of the initial\u2026","rel":"","context":"In \"dielectric\"","block_context":{"text":"dielectric","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=dielectric"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/birch1.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":10279,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=10279","url_meta":{"origin":8508,"position":2},"title":"Hidden intermediates in the (acid catalysed) ring opening of propene epoxide.","author":"Henry Rzepa","date":"May 6, 2013","format":false,"excerpt":"In a previous post on the topic, I remarked how the regiospecific ethanolysis of propene epoxide could be quickly and simply rationalised by inspecting the localized NBO orbital calculated for either the neutral or the protonated epoxide. This is an application of Hammond's postulate[ in extrapolating the properties of a\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\/05\/hidden-intermediate-1.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":23522,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=23522","url_meta":{"origin":8508,"position":3},"title":"A computational mechanism for the aqueous hydrolysis of a ketal to a ketone and alcohol.","author":"Henry Rzepa","date":"April 1, 2021","format":false,"excerpt":"The previous post was about an insecticide and made a point that the persistence of both insecticides and herbicides is an important aspect of their environmental properties. Water hydrolysis will degrade them, a typical residency time being in the order of a few days. I noted in passing a dioxepin-based\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":"","src":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2021\/03\/R-1024x699.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":8570,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=8570","url_meta":{"origin":8508,"position":4},"title":"The mechanism of the Birch reduction. Sequel to benzene reduction.","author":"Henry Rzepa","date":"December 5, 2012","format":false,"excerpt":"I noted briefly in discussing why Birch reduction of benzene gives 1,4-cyclohexadiene (diagram below) that the geometry of the end-stage pentadienyl anion was distorted in the presence of the sodium cation to favour this product. This distortion actually has some pedagogic value, and so I elaborate this here. The starting\u2026","rel":"","context":"In \"antiaromaticity\"","block_context":{"text":"antiaromaticity","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?tag=antiaromaticity"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.ch.imperial.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2012\/12\/benzene-22.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":20354,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=20354","url_meta":{"origin":8508,"position":5},"title":"Epoxidation of ethene: a new substituent twist.","author":"Henry Rzepa","date":"December 21, 2018","format":false,"excerpt":"Five years back,\u00a0I speculated about the mechanism of the epoxidation of ethene by a peracid, concluding that kinetic isotope effects provided interesting evidence that this mechanism is highly asynchronous and involves a so-called \"hidden intermediate\". Here I revisit this reaction in which a small change is applied to the atoms\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":"https:\/\/i0.wp.com\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/12\/imine2.gif?resize=350%2C200&ssl=1","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\/8508","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=8508"}],"version-history":[{"count":29,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8508\/revisions"}],"predecessor-version":[{"id":10311,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=\/wp\/v2\/posts\/8508\/revisions\/10311"}],"wp:attachment":[{"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8508"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8508"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8508"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fppma_author&post=8508"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}