Nuclear Magnetic Resonance Spectra of Systems of the A3B2C Type: Proton Magnetic Resonance Spectra and the Absolute Signs of the Proton-Proton Spin Coupling Constants in Ethyl Acetylene and Ethyl Mercaptan

Abstract

The high-resolution proton magnetic resonance spectra of ethyl acetylene and ethyl mercaptan have been studied at both 40 Mc and 60 Mc. Theoretical analysis of these spectra as systems of the A3B2C type enables one to determine the relative signs of the proton-proton spin coupling constants in these molecules. It is thus shown that the spin coupling constants JCH3–CH2 and JCH2–CH are of opposite sign in ethyl acetylene, while JCH3–CH2 and JCH2–SH in ethyl mercaptan are of the same sign. Making use of the results of the valence bond theory regarding the absolute sign of JCH3–CH2 the present analysis has made possible determinations of the absolute sign of JCH2–CH and JCH2–SH in ethyl acetylene and ethyl mercaptan, respectively.