Twisted C=C Double Bonds with Very Low Rotational Barriers in Dioxanediones and Isoxazolones Determined by Low‐Temperature Dynamic NMR Spectroscopy and Computational Chemistry | Zendy

Wentrup Curt | Zendy; Koch Rainer | Zendy; Kleinpeter Erich | Zendy

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Twisted C=C Double Bonds with Very Low Rotational Barriers in Dioxanediones and Isoxazolones Determined by Low‐Temperature Dynamic NMR Spectroscopy and Computational Chemistry

Author(s) -

Wentrup Curt,

Koch Rainer,

Kleinpeter Erich

Publication year - 2016

Publication title -

european journal of organic chemistry

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 0.825

H-Index - 155

eISSN - 1099-0690

pISSN - 1434-193X

DOI - 10.1002/ejoc.201600931

Subject(s) - chemistry , methylene , double bond , nuclear magnetic resonance spectroscopy , atomic orbital , spectroscopy , carbon 13 nmr , computational chemistry , acceptor , single bond , crystallography , stereochemistry , electron , organic chemistry , group (periodic table) , physics , quantum mechanics , condensed matter physics

Extremely low rotational barriers for ethylenic C=C double bonds in the range 5–17 kcal/mol have been measured by low temperature 1 H and 13 C NMR spectroscopy and confirmed by calculations at the M06‐2X level for 5‐methylene‐1,3‐dioxane‐4,6‐diones (Meldrum's acid derivatives) and 4‐methyleneisoxazol‐5(4 H )‐ones. The barriers are ascribed to the push‐pull (donor‐acceptor) nature of the alkenes. A correlation between the calculated C=C bond lengths and the ratios of electron occupancies in the ethylenic π and π* orbitals (the π/π* quotient) constitutes a useful measure of the push‐pull character.

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