Experimental and DFT studies on the transmission mechanisms of analogous NMR JCH and JCC couplings in 1-X- and 1-X-3-methylbicyclo[1.1.1]-pentanes

✍ Scribed by Rubén H. Contreras; Ángel L. Esteban; Ernesto Díez; Ian J. Lochert; Ernest W. Della; Prof. Cláudio F. Tormena

• Publisher: John Wiley and Sons
• Year: 2007
• Tongue: English
• Weight: 145 KB
• Volume: 45
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.2009

✦ Synopsis

Abstract

The main aim of this work is to compare the transmission mechanisms for the Fermi contact term of spin–spin couplings, SSCCs, in series 1‐X‐bicyclo[1.1.1]‐pentane, (1), and 1‐X‐3‐methylbicyclo[1.1.1]pentane, (2), and from that comparison to gain insight into some subtle aspects of the FC transmission. To this end, 18 members of the latter series were isotopically enriched in ^13^C at the methyl position and the following couplings were measured; ^1^J, ^3^J and ^4^J. These three types of SSCCs in (2) are compared, respectively, with ^1^J, ^3^J and ^4^J in (1); these latter values were taken from previous works. Since electron delocalization plays an important role in the transmission of the FC interaction, the natural bond orbital (NBO) method is employed to quantify electron delocalization interactions within selected members of series (1) and (2). It is found that ^1^J SSCCs in (1) is more efficiently transmitted than ^1^J SSCCs in (2). On the other hand, ^3^J and ^4^J SSCCs in (1) are notably less efficiently transmitted than ^3^J and ^4^J SSCCs in (2), although substituent effects on these two SSCCs show the opposite trends. These different efficiencies are rationalized in terms of different σ‐hyperconjugative interactions in both series of compounds. Copyright © 2007 John Wiley & Sons, Ltd.