{"id":3472,"date":"2011-02-05T15:57:02","date_gmt":"2011-02-05T14:57:02","guid":{"rendered":"http:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=3472"},"modified":"2023-09-17T07:28:58","modified_gmt":"2023-09-17T06:28:58","slug":"a-short-history-of-molecular-modelling-1860-1890","status":"publish","type":"post","link":"https:\/\/www.ch.ic.ac.uk\/rzepa\/blog\/?p=3472","title":{"rendered":"A short history of molecular modelling: 1860-1890."},"content":{"rendered":"
\n

In 1953, the model of the DNA molecule\u00a0led to what has become regarded as the most\u00a0famous<\/a> scientific diagram\u00a0of the 20th century. It had all started 93 years earlier in\u00a01860, at a time when the tetravalency of carbon was only just established (by William Odling) and the concept of atoms as real entities was to remain controversial for another\u00a045<\/a> years (for example Faraday, perhaps the most famous scientist alive in 1860 did not believe atoms were real). So the idea of constructing a molecular model from atoms as the basis for understanding chemical behaviour was perhaps bolder than we might think. It is shown below, part of a set built for August Wilhelm von Hofmann<\/a> as part of the lectures he delivered at the Royal\u00a0College of\u00a0Chemistry in London (now Imperial College).<\/p>\n

\"\"<\/a>

The original August Wilhelm von Hofmann molecular model, located in the archives at the Royal institution, London and used by Hofmann in his 1865 lecture there<\/p><\/div>\n

This grand-daddy of all molecular models does have some interesting features. The most obvious is that the carbon atom at the centre is square planar (tetrahedral carbon was still 14 years in the future). What HAS survived to the present day is the colour scheme used (black=carbon, white=hydrogen, and not shown here, red=oxygen, blue=nitrogen, green=chlorine). \u00a0But another noteworthy aspect is the relative size of the white hydrogen, which is larger than the black carbon. This deficiency was however very soon rectified in 1861 by Josef Loschmidt, who published \u00a0a famous pamphlet<\/a> in which he set out his ideas for the structures of more than \u00a0270 molecules (many of which by the way were cyclic, and this some four years before\u00a0Kekule’s dream!). An example (#239) is shown below, which gets the relative sizes of the atoms more or less correct (OK, chlorine is shown with rather an odd shape). To get an idea of how good Loschmidt’s model actually was, click on the diagram to load a modern model, and compare the two! Even more impressive, these diagrams pre-date van der Waals<\/a> work on the finite sizes of atoms, first presented in 1873.<\/p>\n

\"\"

Loschmidt’s molecular models. Click for 3D<\/p><\/div>\n

To conclude, I cannot resist showing one more model. Hermann Sachse<\/a> believed cyclohexane could not be planar. To try to convince people, in 1890 he included a \u00a0“flat-packed” model in the pages of a journal article, \u00a0evidently believing that people would cut it out, and assemble it into a\u00a03D shape.<\/p>\n

\"\"<\/a>

Flat-packed molecular model of cyclohexane<\/p><\/div>\n

You might have noticed a theme in the present blog of presenting 3D models for many of the molecules I discuss (include the Loschmidt one above). For the historians amongst you, I note our 1995 article<\/a> in which we updated[1]<\/a><\/span> Sachse’s origami with an article featuring how to incorporate interactive models into journals (still sadly only too rare). Perhaps a history of the molecular model, and how it has been presented over 150 years might be an interesting one to trace!<\/p>\n

\n

Acknowledgments<\/h4>\n

This post has been cross-posted in PDF format at Authorea<\/a>.<\/p>\n

References<\/h2>\n
  1. O. Casher, G.K. Chandramohan, M.J. Hargreaves, C. Leach, P. Murray-Rust, H.S. Rzepa, R. Sayle, and B.J. Whitaker, \"Hyperactive molecules and the World-Wide-Web information system\", Journal of the Chemical Society, Perkin Transactions 2<\/i>, pp. 7, 1995. https:\/\/doi.org\/10.1039\/p29950000007<\/a>\n\n<\/li>\n<\/ol>\n\n<\/div> ","protected":false},"excerpt":{"rendered":"

    In 1953, the model of the DNA molecule\u00a0led to what has become regarded as the most\u00a0famous scientific diagram\u00a0of the 20th century. It had all started 93 years earlier in\u00a01860, at a time when the tetravalency of carbon was only just established (by William Odling) and the concept of atoms as real entities was to remain […]<\/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":true,"_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}},"categories":[1],"tags":[440,26,445,179,2651,406,37,444,407,438,439,436,405,435,441,408,437,373,442,443],"ppma_author":[2661],"class_list":["post-3472","post","type-post","status-publish","format-standard","hentry","category-general","tag-and-compare-the-two","tag-chemical-behaviour","tag-deficiency","tag-hermann-sachse","tag-historical","tag-hofmann","tag-imperial-college","tag-josef-loschmidt","tag-loschmidt","tag-model","tag-modern-model","tag-molecular-model","tag-odling","tag-royal-college-of-chemistry","tag-royal-college-of-chemistry-in-london","tag-sachse","tag-scientist","tag-tutorial-material","tag-wilhelm-von-hofmann","tag-william-odling"],"yoast_head":"\nA short history of molecular modelling: 1860-1890. - 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=3472\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"A short history of molecular modelling: 1860-1890. - Henry Rzepa's Blog\" \/>\n<meta property=\"og:description\" content=\"In 1953, the model of the DNA molecule\u00a0led to what has become regarded as the most\u00a0famous scientific diagram\u00a0of the 20th century. 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