Absolute Correlation of Nuclear Spin—Spin Coupling Constants with Atomic Number. II. CouplingsJX–C–HandJX—H

Abstract

A precise correlation of nuclear spin—spin coupling constants J X—Y is presented for molecules where X and Y are bonded or separated by a common atom in a series. If X is a central atom surrounded by equivalent Y atoms with no lone pair electrons and X varies down a group of the periodic table a relationship (J X − Y /γ X γ Y ) 1 2 =AZ X +B is obeyed where Z X is the atomic number of the element X. A and B are experimental constants to be determined. The constants A and B have been determined from literature values of coupling constants for the series J X—H and J X–C–H where X is a Group IV atom. In future work further series will be investigated. Unknown coupling constants in a symmetrical series can be predicted accurately by use of the equation. Deviations from the correlation are expressed in terms of a deviation parameter ``D.'' The series (CH3)4Sn, (CH3)3SnH, (CH3)2SnH2, (CH3)SnH3, and SnH4 is investigated in terms of a defined deviation parameter. Positive deviations are shown to be regular in the series for J Sn–C–H indicating increased ``s'' character in the Sn–C bond and corresponding negative deviations are noted for J Sn–H in this series with decreasing s character in the Sn–H bond. A relative deviation parameter is suggested for a given set of molecules with slightly distorted symmetry which has not yet been investigated fully for a series of molecules. The correlation fails when J X—H and J X–C–H are considered and X has a low atomic number. The interpretation on the basis of hyperfine splitting constants of the single s electron in the alkali metals suggests that such deviations are expected.