Unexpected behavior of the 3JCH coupling constant in unsaturated compounds |
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Authors: | Uenifer Rodrigues Couto Armando Navarro-Vázquez Cláudio Francisco Tormena |
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Affiliation: | 1. Institute of Chemistry, University of Campinas, Campinas, Brazil;2. Departamento de Química Fundamental, CCEN, Universidade Federal de Pernambuco, Cidade Universitária, Recife, Brazil |
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Abstract: | The experimental and theoretical behavior of the (OC) CC H 3JCH coupling constant is investigated for a series of α,β-unsaturated compounds ( 1 to 8 ), and for some of them, the well-known relationship (3JCHcis < 3JCHtrans) was observed. However, for some compounds, close values for 3JCHcis and 3JCHtrans couplings were observed, and for aldehydes group containing compounds ( 7 and 8 E), an inversion order is observed (3JCHcis > 3JCHtrans). In all cases where the 3JCHcis < 3JCHtrans relationship it is not followed, a polar group or electronegative atom oriented in opposite direction (s-trans) to the H CC hydrogen is present, suggesting that conformational preference of such polar group or atoms are important factor on the behavior of 3JCH couplings. Taking all of these in consideration, a new Karplus-type equation was proposed for 3JCH couplings in α,β-unsaturated compounds, which can be used for configurational and conformational assignment on trisubstituted double bond derivatives. |
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Keywords: | 3JCH coupling constant Karplus-type equation unsaturated compounds |
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