Concerning the Question: Does Quantum Mechanics Predict Molecular Structure? An Examination of the Energetics

Concerning the Question: Does Quantum Mechanics Predict Molecular Structure? An Examination of the Energetics | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Concerning the Question: Does Quantum Mechanics Predict Molecular Structure? An Examination of the Energetics Mark Randel Leach This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7989844/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract There is a controversy concerning the role of the Born-Oppenheimer approximation (BOA) in molecular orbital calculations. Some philosophers argue that because the BOA clamps the position of the nuclei in space the BOA fixes the outcome of the calculation, thus calling into question the calculation’s legitimacy. As a contribution to the debate, we perform a thermochemical analysis to determine the absolute energies of the quantum Hamiltonian operator, Ĥψ , in kJmol –1 , with respect to the constitutional isomers ethanol and dimethyl ether and their constituent particles. Our results show that the difference between the quantum Hamiltonian enthalpies, the Δ QH H , is tiny, − 407,023 kJmol – 1 vs . − 407,116 kJmol –1 , a 0.02% difference, which is far smaller than the ~ 1% chemical error deemed acceptable/tolerable in many chemical procedures and calculations. Quantum Hamiltonian Born-Oppenheimer approximation molecular orbital theory molecular structure enthalpy cycles chemical error Full Text Additional Declarations No competing interests reported. Supplementary Files QHC2H6O.xlsx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 28 Feb, 2026 Reviews received at journal 16 Feb, 2026 Reviewers agreed at journal 11 Feb, 2026 Reviewers invited by journal 10 Feb, 2026 Editor assigned by journal 30 Oct, 2025 Submission checks completed at journal 30 Oct, 2025 First submitted to journal 30 Oct, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7989844","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":589849170,"identity":"25b0a40d-ed81-4a4e-aa85-299e2c32354b","order_by":0,"name":"Mark Randel Leach","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9UlEQVRIiWNgGAWjYHACZoYPCM4BEJ+wFsYZDAwSEHYCkVqYeVC0EAK67WcfG9vm2NTxN7A/ky78cUdOvp39AcOPim04tZidSTdOzt2WJiFxgMdMekbCM2ODwzwGjD1nbuPWciCN+XDutsMSDPffsEnzJBxO3AB0JzNjGx4t558xH7bc9l9C/gDQYUAt9fOb2R/g13IjjTmZcdsBCYMDDGYgLQkMhxkMCGh5xmzYuy1ZcuMBHmNrnrTDhhuAfjmI1y/n05glfm6z45c7wP7wNo/NYXn5/uMPH/yowK0FGbBIwFgHiFIPBMwfCKsZBaNgFIyCkQgA5qNTS/dZmYsAAAAASUVORK5CYII=","orcid":"","institution":"","correspondingAuthor":true,"prefix":"","firstName":"Mark","middleName":"Randel","lastName":"Leach","suffix":""}],"badges":[],"createdAt":"2025-10-30 13:23:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7989844/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7989844/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":102962805,"identity":"f17f5718-e7aa-4098-8e73-7854d6ab9e55","added_by":"auto","created_at":"2026-02-19 04:11:21","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":990196,"visible":true,"origin":"","legend":"","description":"","filename":"ATQQTandMolStrucv3.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7989844/v1_covered_7ce3d892-8806-48ad-8220-4751f4d128e6.pdf"},{"id":102776909,"identity":"68637656-f31b-4934-b7ba-03d23710ccce","added_by":"auto","created_at":"2026-02-16 14:11:17","extension":"xlsx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":21789,"visible":true,"origin":"","legend":"","description":"","filename":"QHC2H6O.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-7989844/v1/946a71e8e5cc7a8bc8f81211.xlsx"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eConcerning the Question: Does Quantum Mechanics Predict Molecular Structure? 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Some philosophers argue that because the BOA \u003cem\u003eclamps\u003c/em\u003e the position of the nuclei in space the BOA \u003cem\u003efixes\u003c/em\u003e the outcome of the calculation, thus calling into question the calculation\u0026rsquo;s legitimacy. As a contribution to the debate, we perform a thermochemical analysis to determine the absolute energies of the quantum Hamiltonian operator, \u003cem\u003eĤψ\u003c/em\u003e, in kJmol\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, with respect to the constitutional isomers ethanol and dimethyl ether and their constituent particles. Our results show that the difference between the quantum Hamiltonian enthalpies, the Δ\u003csub\u003eQH\u003c/sub\u003e\u003cem\u003eH\u003c/em\u003e, is tiny, \u0026minus;\u0026thinsp;407,023 kJmol\u003csup\u003e\u0026ndash;\u003c/sup\u003e1 \u003cem\u003evs\u003c/em\u003e. \u0026minus;\u0026thinsp;407,116 kJmol\u003csup\u003e\u0026ndash;1\u003c/sup\u003e, a 0.02% difference, which is far smaller than the ~\u0026thinsp;1% chemical error deemed acceptable/tolerable in many chemical procedures and calculations.\u003c/p\u003e","manuscriptTitle":"Concerning the Question: Does Quantum Mechanics Predict Molecular Structure? 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