{"id":19983,"date":"2018-08-25T08:37:04","date_gmt":"2018-08-25T07:37:04","guid":{"rendered":"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=19983"},"modified":"2018-09-06T06:47:05","modified_gmt":"2018-09-06T05:47:05","slug":"organocatalytic-cyclopropanation-of-an-enal-computational-mechanistic-understanding","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983","title":{"rendered":"Organocatalytic cyclopropanation of an enal: (computational)  mechanistic understanding."},"content":{"rendered":"<div class=\"kcite-section\" kcite-section-id=\"19983\">\n<p>Symbiosis between computation and experiment is increasingly evident in pedagogic journals such as <i>J. Chemical Education<\/i>. Thus an example of original laboratory experiments<span id=\"cite_ITEM-19983-0\" name=\"citation\"><a href=\"#ITEM-19983-0\">[1]<\/a><\/span>,<span id=\"cite_ITEM-19983-1\" name=\"citation\"><a href=\"#ITEM-19983-1\">[2]<\/a><\/span> that later became twinned with a computational counterpart.<span id=\"cite_ITEM-19983-2\" name=\"citation\"><a href=\"#ITEM-19983-2\">[3]<\/a><\/span> So when I spotted this recent lab experiment<span id=\"cite_ITEM-19983-3\" name=\"citation\"><a href=\"#ITEM-19983-3\">[4]<\/a><\/span> I felt another twinning approaching.<\/p>\n<p>The reaction under consideration is that between dec-2-enal and 2,4-dinitrobenzyl chloride as catalysed by an \u03b1,\u03b1-diphenylprolinol trimethylsilyl ester with addition of further base (di-isopropylamine?). The proposed mechanism can be seen in figure 7<sup>\u2021<\/sup> of the journal article<span id=\"cite_ITEM-19983-3\" name=\"citation\"><a href=\"#ITEM-19983-3\">[4]<\/a><\/span> and also scheme 2 of an earlier article.<span id=\"cite_ITEM-19983-4\" name=\"citation\"><a href=\"#ITEM-19983-4\">[5]<\/a><\/span> The following is my interpretation of their published mechanism (the compound numbering is the same as in Figure 7).<\/p>\n<ol>\n<li>The initiating step is the condensation between the alkyl enal (<strong>1<\/strong>) and the prolinol derivative (<strong>3<\/strong>), with elimination of water and the formation of a positive iminium cation (<strong>5<\/strong>). One might wonder at this stage what the counter ion to this cation is.<\/li>\n<li><strong>5<\/strong> then reacts with&nbsp;2,4-dinitrobenzyl chloride (<strong>2<\/strong>) with apparent elimination of HCl to form <strong>6<\/strong>. This corresponds to 1,4-Michael addition to <strong>5<\/strong> with the formation of the first new &nbsp;C-C bond and the creation of two new stereogenic centres.<\/li>\n<li><strong>6<\/strong> then cyclises to form a second new C-C bond and a third new stereogenic centre as in <strong>7<\/strong>.<\/li>\n<li><strong>7<\/strong> is then hydrolysed to give the final product <strong>4<\/strong>.<\/li>\n<\/ol>\n<p>A total of three (starred) stereogenic centres are therefore created in <strong>4<\/strong>, implying 2<sup>3<\/sup> = 8 steroisomers, arranged as four diastereomers and their enantiomers. A computational mechanistic analysis might strive to cast light on the following questions.<\/p>\n<ul>\n<li>Is the sequence shown in figure 7 reasonable? If not can a more reasonable cycle be constructed that has energetics corresponding to a facile reaction at 0&deg;C?<\/li>\n<li>What are the predicted relative yields of the four possible diastereomeric products and do they match those observed?\n<\/li>\n<li>If &nbsp;R=\u03b1,\u03b1-diphenylprolinol trimethylsilyl ester, then this fourth chiral centre increases the total number of stereoisomers to 16, arranged in eight pairs of diastereomers. Does this result in the diastereomers of <strong>4<\/strong> forming with an excess of one enantiomer over the other (an ee &ne; 0)?<\/li>\n<\/ul>\n<p>This post addresses just the first question (R=R&#8217;=H, R&#8221;=isopropylamine) leaving the other two questions for later analysis.<\/p>\n<p><a href=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/Figure7.svg\"><img decoding=\"async\" class=\"aligncenter size-large wp-image-19987\" src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/Figure7.svg\" alt=\"\" width=\"540\" \/><\/a><\/p>\n<p>My analysis (figure above)<sup>&hearts;<\/sup> of the mechanism, as cast for computational analysis<sup>&dagger;<\/sup>, differs in various details from Figure 7\/Scheme 2 of the published articles.<span id=\"cite_ITEM-19983-3\" name=\"citation\"><a href=\"#ITEM-19983-3\">[4]<\/a><\/span>,<span id=\"cite_ITEM-19983-4\" name=\"citation\"><a href=\"#ITEM-19983-4\">[5]<\/a><\/span><\/p>\n<ol start=\"5\">\n<li>The issue of defining a counterion to <strong>5<\/strong> is solved by in fact starting the cycle with proton abstraction from <strong>2<\/strong> by di-isopropylamine<sup>&diams;<\/sup> to form a benzylic anion, as stabilized by the 2,4-dinitro groups and with the positive counter-ion being the protonated amine base.<\/li>\n<li>The next step is reaction between <strong>1<\/strong> and <strong>3<\/strong> to form an aminol <b>10<\/b>, a tetrahedral intermediate.<\/li>\n<li>To remove water from this to form an iminium cation <b>5<\/b>, one has to protonate the hydroxy group and this can now be done using the cationic ammonium species formed in step 5 above.<\/li>\n<li>The benzylic anion can now react with the iminium cation to form the first C-C bond and the first two stereocentres <i>via<\/i> 1,4-Michael addition to form <b>6<\/b><\/li>\n<li>The species <b>6<\/b> can now eliminate chloride anion to form the cyclopropyl iminium cation\/anion pair <b>7<\/b>, generating the 3rd stereogenic centre.<\/li>\n<li>Hydrolysis forms the product <b>4<\/b> and returns the system to the starting point in the catalytic cycle.<\/li>\n<li>Also included is whether an alternative mechanism is viable, involving elimination of Cl<sup>&#8211;<\/sup> from <b>8<\/b> to form a &#8220;carbene&#8221;, which could then potentially add to the alkene in <b>1<\/b>.\n<\/li>\n<\/ol>\n<table border=\"1\">\n<tbody>\n<tr>\n<th>\n<p>Species (transition state)<\/p>\n<p>FAIR Data DOI<br \/>\n<a href=\"https:\/\/data.hpc.imperial.ac.uk\/resolve?doi=4642\">10.14469\/hpc\/4642<\/a><\/p>\n<\/th>\n<th>\n<p>\u0394G<sub>273.15<\/sub>, Hartree<br \/>\n(\u0394\u0394G<sup>&Dagger;<\/sup><sub>273.15<\/sub>, kcal\/mol)\n<\/p>\n<\/th>\n<th>\n<p>Structure<br \/>(click for 3D model)<\/p>\n<\/th>\n<\/tr>\n<tr>\n<td>Reactants<\/td>\n<td><a href=\"https:\/\/search.datacite.org\/works?query=subjectScheme:Gibbs_energy+subject:-1837.174744\">-1837.174744<\/a><sup>&clubs;<\/sup> (0.0)<\/td>\n<td><img decoding=\"async\" class=\"size-full wp-image-19841\" onclick=\"jmolApplet([200,200],'load wp-content\/uploads\/2018\/08\/OC-reactant.log;frame 50;spin 3;','c1');\"  src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/reactant-e1535017188641.jpg\" alt=\"\" width=\"200\" \/><\/td>\n<\/tr>\n<tr>\n<td>TS1<\/td>\n<td><a href=\"https:\/\/search.datacite.org\/works?query=subjectScheme:Gibbs_energy+subject:-1837.150502\">-1837.150502<\/a> (15.2)<\/td>\n<td><img decoding=\"async\" onclick=\"jmolApplet([200,200],'load wp-content\/uploads\/2018\/08\/OC-TS1.log;frame 6;vectors on;vectors 4;vectors scale 4.0;color vectors green;vibration 6;spin 3;','c2');\"  src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/OC-TS1.jpg\" alt=\"\" width=\"200\" \/><\/td>\n<\/tr>\n<tr>\n<td>TS2<\/td>\n<td><a href=\"https:\/\/search.datacite.org\/works?query=subjectScheme:Gibbs_energy+subject:-1837.154923\">-1837.154923<\/a> (12.4)<\/td>\n<td><img decoding=\"async\" onclick=\"jmolApplet([200,200],'load wp-content\/uploads\/2018\/08\/OC-TS2.log;frame 2;vectors on;vectors 4;vectors scale 4.0;color vectors green;vibration 6;spin 3;','c3');\"  src=\"wp-content\/uploads\/2018\/08\/OC-TS2.jpg\" alt=\"\" width=\"200\" \/><\/td>\n<\/tr>\n<tr>\n<td>TS3<\/td>\n<td><a href=\"https:\/\/search.datacite.org\/works?query=subjectScheme:Gibbs_energy+subject:-1837.147927\">-1837.147927<\/a> (16.8)<\/td>\n<td><img decoding=\"async\" onclick=\"jmolApplet([200,200],'load wp-content\/uploads\/2018\/08\/OC-TS3.log;frame 7;vectors on;vectors 4;vectors scale 4.0;color vectors green;vibration 6;spin 3;','c4');\"  src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/OC-TS3.jpg\" alt=\"\" width=\"200\" \/><\/td>\n<\/tr>\n<tr>\n<td>TS4<\/td>\n<td><a href=\"https:\/\/search.datacite.org\/works?query=subjectScheme:Gibbs_energy+subject:-1837.175723\">-1837.175723<\/a> (-0.6)<\/td>\n<td><img decoding=\"async\" onclick=\"jmolApplet([200,200],'load wp-content\/uploads\/2018\/08\/OC-TS4.log;frame 2;vectors on;vectors 4;vectors scale 4.0;color vectors green;vibration 6;spin 3;','c5');\"  src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/OC-TS4.jpg\" alt=\"\" width=\"200\" \/><\/td>\n<\/tr>\n<tr>\n<td>TS5<\/td>\n<td><a href=\"https:\/\/search.datacite.org\/works?query=subjectScheme:Gibbs_energy+subject:-1837.101534\">-1837.101534<\/a> (45.9)<\/td>\n<td><img decoding=\"async\" onclick=\"jmolApplet([200,200],'load wp-content\/uploads\/2018\/08\/OC-TS5.log;frame 28;vectors on;vectors 4;vectors scale 4.0;color vectors green;vibration 6;spin 3;','c6');\"  src=\"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/OC-TS5.jpg\" alt=\"\" width=\"200\" \/><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>The (relative) free energies of the transition states at the B3LYP+GD3BJ\/6-311G(d,p)\/SCRF=chloroform level shown in the table above (click on the thumbnail images to show the 3D model of each transition state) reveal that the highest point corresponds to <b>TS3<\/b>, a C-C bond forming reaction. This is noteworthy because it constitutes the reaction between an ion-pair, albeit ions which are both heavily stabilized by delocalisation. Since the reaction is known to proceed over 3 hours at 0&deg;C, the activation barrier of 16.8 kcal\/mol is also entirely reasonable. <b>TS5<\/b>, the putative formation of a carbene from the benzyl chloride, has a very high barrier and in fact cyclises to form <b>9<\/b>. This pathway can therefore be safely ignored.<\/p>\n<p>The next stage would be to investigate the stereochemical implications of this mechanism (atoms in <b>4<\/b> marked with a <b>*<\/b>) using the actual substituents for R and R&#8217;. Because the mechanism includes ion-pairs throughout, this does actually present some tricky issues. Unlike molecules with covalent bonds, where the shapes are relatively easy to predict, ion-pairs are more flexible and can often adopt a variety of poses, the relative energy of which is frequently determined simply by the magnitudes of their dipole moments.<span id=\"cite_ITEM-19983-5\" name=\"citation\"><a href=\"#ITEM-19983-5\">[6]<\/a><\/span> If I manage to sort this out, I will report back here.<\/p>\n<hr \/>\n<p><sup>\u2021<\/sup>I would love to show you figure 7 here, but the publisher asserts that I would need to pay them $87.75 to do so and so you will have to acquire the article yourself to see it.<\/p>\n<p><sup>&dagger;<\/sup>Various guiding rules include constructing the entire catalytic cycle using exactly the same number of atoms so that the cycle can show only relative (free) energies and using neutral ion-pair models rather than just charged species alone.<\/p>\n<p><sup>&hearts;<\/sup>Almost all the chemical diagrams on this blog for some ten years now have been in SVG (scalable vector graphics) format. Most modern web browsers for a number of years now have had excellent support for SVG. Until recently SVG could not be generated directly from a drawing program such as <i>e.g.<\/i> ChemDraw. Instead I saved as EPS (encapsulated postscript) and then used a program called <b><a href=\"https:\/\/www.scribus.net\" rel=\"noopener\" target=\"_blank\">Scribus<\/a><\/b> to convert to SVG. In fact with Chemdraw V18.0, the direct conversion to SVG seems to be working very well, including honoring color maps. To scale up a diagram, click on it to open a new browser window containing only it and then use the browser zoom-in control to magnify it. Unlike <i>e.g.<\/i> a pixel image, SVG images magnify\/scale correctly. <\/p>\n<p><sup>&clubs;<\/sup>This relates to metadata as described in <a href=\"https:\/\/www.ch.imperial.ac.uk\/rzepa\/blog\/?p=19892\" rel=\"noopener\" target=\"_blank\">this post<\/a> in performing a global search of any species matching this Gibbs Energy.<\/p>\n<p><sup>&diams;<\/sup>If the mechanism is set up without any base, then proton abstraction must occur directly from the benzyl chloride.  Under these circumstances, the barrier for proton removal is 27.5 kcal\/mol, whilst that for C-C bond formation is only 13.6.<\/p>\n<h2>References<\/h2>\n    <ol class=\"kcite-bibliography csl-bib-body\"><li id=\"ITEM-19983-0\">A. Burke, P. Dillon, K. Martin, and T.W. Hanks, \"Catalytic Asymmetric Epoxidation Using a Fructose-Derived Catalyst\", <i>Journal of Chemical Education<\/i>, vol. 77, pp. 271, 2000. <a href=\"https:\/\/doi.org\/10.1021\/ed077p271\">https:\/\/doi.org\/10.1021\/ed077p271<\/a>\n\n<\/li>\n<li id=\"ITEM-19983-1\">J. Hanson, \"Synthesis and Use of Jacobsen&#039;s Catalyst: Enantioselective Epoxidation in the Introductory Organic Laboratory\", <i>Journal of Chemical Education<\/i>, vol. 78, pp. 1266, 2001. <a href=\"https:\/\/doi.org\/10.1021\/ed078p1266\">https:\/\/doi.org\/10.1021\/ed078p1266<\/a>\n\n<\/li>\n<li id=\"ITEM-19983-2\">K.K.(. Hii, H.S. Rzepa, and E.H. Smith, \"Asymmetric Epoxidation: A Twinned Laboratory and Molecular Modeling Experiment for Upper-Level Organic Chemistry Students\", <i>Journal of Chemical Education<\/i>, vol. 92, pp. 1385-1389, 2015. <a href=\"https:\/\/doi.org\/10.1021\/ed500398e\">https:\/\/doi.org\/10.1021\/ed500398e<\/a>\n\n<\/li>\n<li id=\"ITEM-19983-3\">M. Meazza, A. Kowalczuk, S. Watkins, S. Holland, T.A. Logothetis, and R. Rios, \"Organocatalytic Cyclopropanation of (&lt;i&gt;E&lt;\/i&gt;)-Dec-2-enal: Synthesis, Spectral Analysis and Mechanistic Understanding\", <i>Journal of Chemical Education<\/i>, vol. 95, pp. 1832-1839, 2018. <a href=\"https:\/\/doi.org\/10.1021\/acs.jchemed.7b00566\">https:\/\/doi.org\/10.1021\/acs.jchemed.7b00566<\/a>\n\n<\/li>\n<li id=\"ITEM-19983-4\">M. Meazza, M. Ashe, H.Y. Shin, H.S. Yang, A. Mazzanti, J.W. Yang, and R. Rios, \"Enantioselective Organocatalytic Cyclopropanation of Enals Using Benzyl Chlorides\", <i>The Journal of Organic Chemistry<\/i>, vol. 81, pp. 3488-3500, 2016. <a href=\"https:\/\/doi.org\/10.1021\/acs.joc.5b02801\">https:\/\/doi.org\/10.1021\/acs.joc.5b02801<\/a>\n\n<\/li>\n<li id=\"ITEM-19983-5\">J. Clarke, K.J. Bonney, M. Yaqoob, S. Solanki, H.S. Rzepa, A.J.P. White, D.S. Millan, and D.C. Braddock, \"Epimeric Face-Selective Oxidations and Diastereodivergent Transannular Oxonium Ion Formation Fragmentations: Computational Modeling and Total Syntheses of 12-Epoxyobtusallene IV, 12-Epoxyobtusallene II, Obtusallene X, Marilzabicycloallene C, and Marilzabicycloallene D\", <i>The Journal of Organic Chemistry<\/i>, vol. 81, pp. 9539-9552, 2016. <a href=\"https:\/\/doi.org\/10.1021\/acs.joc.6b02008\">https:\/\/doi.org\/10.1021\/acs.joc.6b02008<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> <!-- kcite-section 19983 -->","protected":false},"excerpt":{"rendered":"<p>Symbiosis between computation and experiment is increasingly evident in pedagogic journals such as J. Chemical Education. Thus an example of original laboratory experiments, that later became twinned with a computational counterpart. So when I spotted this recent lab experiment I felt another twinning approaching. The reaction under consideration is that between dec-2-enal and 2,4-dinitrobenzyl chloride [&hellip;]<\/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":true,"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":[1712,2481,1527,320,1395,832,835,1412,2480,2482,2479,1410,2483,1196,705,1257],"ppma_author":[2661],"class_list":["post-19983","post","type-post","status-publish","format-standard","hentry","category-interesting-chemistry","tag-ammonium","tag-benzyl-group","tag-cations","tag-chemical-diagrams","tag-chemistry","tag-condensation","tag-final-product","tag-functional-groups","tag-iminium","tag-methyl-group","tag-name-reactions","tag-organic-chemistry","tag-possible-diastereomeric-products","tag-relative-energy","tag-vector-graphics","tag-web-browsers"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.6 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Organocatalytic cyclopropanation of an enal: (computational) mechanistic understanding. - 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=19983\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Organocatalytic cyclopropanation of an enal: (computational) mechanistic understanding. - Henry Rzepa&#039;s Blog\" \/>\n<meta property=\"og:description\" content=\"Symbiosis between computation and experiment is increasingly evident in pedagogic journals such as J. 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Chemical Education. Thus an example of original laboratory experiments, that later became twinned with a computational counterpart. So when I spotted this recent lab experiment I felt another twinning approaching. The reaction under consideration is that between dec-2-enal and 2,4-dinitrobenzyl chloride [&hellip;]","og_url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983","og_site_name":"Henry Rzepa&#039;s Blog","article_published_time":"2018-08-25T07:37:04+00:00","article_modified_time":"2018-09-06T05:47:05+00:00","og_image":[{"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/Figure7.svg","type":"","width":"","height":""}],"author":"Henry Rzepa","twitter_card":"summary_large_image","twitter_misc":{"Written by":"Henry Rzepa","Estimated reading time":"6 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"Article","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983#article","isPartOf":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983"},"author":{"name":"Henry Rzepa","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/#\/schema\/person\/2b40f7b9c872a4dc1547e040a11b6281"},"headline":"Organocatalytic cyclopropanation of an enal: (computational) mechanistic understanding.","datePublished":"2018-08-25T07:37:04+00:00","dateModified":"2018-09-06T05:47:05+00:00","mainEntityOfPage":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983"},"wordCount":1116,"commentCount":9,"image":{"@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983#primaryimage"},"thumbnailUrl":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/wp-content\/uploads\/2018\/08\/Figure7.svg","keywords":["Ammonium","Benzyl group","Cations","chemical diagrams","Chemistry","condensation","final product","Functional groups","Iminium","Methyl group","Name reactions","Organic chemistry","possible diastereomeric products","relative energy","Vector Graphics","web browsers"],"articleSection":["Interesting chemistry"],"inLanguage":"en-GB","potentialAction":[{"@type":"CommentAction","name":"Comment","target":["https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983#respond"]}]},{"@type":"WebPage","@id":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983","url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19983","name":"Organocatalytic cyclopropanation of an enal: (computational) mechanistic understanding. - 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It is thought that the concept originated in December 1995 here at Imperial and in January 1996 at\u2026","rel":"","context":"In &quot;crystal_structure_mining&quot;","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\/2016\/12\/ferris.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":19339,"url":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=19339","url_meta":{"origin":19983,"position":5},"title":"Multispectral Chiral Imaging with a Metalens.","author":"Henry Rzepa","date":"January 6, 2018","format":false,"excerpt":"The title here is from an article on metalenses which caught my eye. Metalenses are planar and optically thin layers which can be manufactured using a single-step lithographic process. 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